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Date: Tue, 27 Sep 2022 16:20:37 +1000
From: Alistair Popple <apopple@...dia.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: akpm@...ux-foundation.org, Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.cz>, "Darrick J. Wong" <djwong@...nel.org>,
Jason Gunthorpe <jgg@...dia.com>,
Christoph Hellwig <hch@....de>,
John Hubbard <jhubbard@...dia.com>,
linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
linux-xfs@...r.kernel.org, linux-mm@...ck.org,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 12/18] devdax: Move address_space helpers to the DAX
core
Dan Williams <dan.j.williams@...el.com> writes:
[...]
> +/**
> + * dax_zap_mappings_range - find first pinned page in @mapping
> + * @mapping: address space to scan for a page with ref count > 1
> + * @start: Starting offset. Page containing 'start' is included.
> + * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
> + * pages from 'start' till the end of file are included.
> + *
> + * DAX requires ZONE_DEVICE mapped pages. These pages are never
> + * 'onlined' to the page allocator so they are considered idle when
> + * page->count == 1. A filesystem uses this interface to determine if
Minor nit-pick I noticed while reading this but shouldn't that be
"page->count == 0" now?
> + * any page in the mapping is busy, i.e. for DMA, or other
> + * get_user_pages() usages.
> + *
> + * It is expected that the filesystem is holding locks to block the
> + * establishment of new mappings in this address_space. I.e. it expects
> + * to be able to run unmap_mapping_range() and subsequently not race
> + * mapping_mapped() becoming true.
> + */
> +struct page *dax_zap_mappings_range(struct address_space *mapping, loff_t start,
> + loff_t end)
> +{
> + void *entry;
> + unsigned int scanned = 0;
> + struct page *page = NULL;
> + pgoff_t start_idx = start >> PAGE_SHIFT;
> + pgoff_t end_idx;
> + XA_STATE(xas, &mapping->i_pages, start_idx);
> +
> + /*
> + * In the 'limited' case get_user_pages() for dax is disabled.
> + */
> + if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> + return NULL;
> +
> + if (!dax_mapping(mapping))
> + return NULL;
> +
> + /* If end == LLONG_MAX, all pages from start to till end of file */
> + if (end == LLONG_MAX)
> + end_idx = ULONG_MAX;
> + else
> + end_idx = end >> PAGE_SHIFT;
> + /*
> + * If we race get_user_pages_fast() here either we'll see the
> + * elevated page count in the iteration and wait, or
> + * get_user_pages_fast() will see that the page it took a reference
> + * against is no longer mapped in the page tables and bail to the
> + * get_user_pages() slow path. The slow path is protected by
> + * pte_lock() and pmd_lock(). New references are not taken without
> + * holding those locks, and unmap_mapping_pages() will not zero the
> + * pte or pmd without holding the respective lock, so we are
> + * guaranteed to either see new references or prevent new
> + * references from being established.
> + */
> + unmap_mapping_pages(mapping, start_idx, end_idx - start_idx + 1, 0);
> +
> + xas_lock_irq(&xas);
> + xas_for_each(&xas, entry, end_idx) {
> + if (WARN_ON_ONCE(!xa_is_value(entry)))
> + continue;
> + if (unlikely(dax_is_locked(entry)))
> + entry = get_unlocked_entry(&xas, 0);
> + if (entry)
> + page = dax_zap_pages(&xas, entry);
> + put_unlocked_entry(&xas, entry, WAKE_NEXT);
> + if (page)
> + break;
> + if (++scanned % XA_CHECK_SCHED)
> + continue;
> +
> + xas_pause(&xas);
> + xas_unlock_irq(&xas);
> + cond_resched();
> + xas_lock_irq(&xas);
> + }
> + xas_unlock_irq(&xas);
> + return page;
> +}
> +EXPORT_SYMBOL_GPL(dax_zap_mappings_range);
> +
> +struct page *dax_zap_mappings(struct address_space *mapping)
> +{
> + return dax_zap_mappings_range(mapping, 0, LLONG_MAX);
> +}
> +EXPORT_SYMBOL_GPL(dax_zap_mappings);
> +
> +static int __dax_invalidate_entry(struct address_space *mapping, pgoff_t index,
> + bool trunc)
> +{
> + XA_STATE(xas, &mapping->i_pages, index);
> + int ret = 0;
> + void *entry;
> +
> + xas_lock_irq(&xas);
> + entry = get_unlocked_entry(&xas, 0);
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + goto out;
> + if (!trunc && (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) ||
> + xas_get_mark(&xas, PAGECACHE_TAG_TOWRITE)))
> + goto out;
> + dax_disassociate_entry(entry, mapping, trunc);
> + xas_store(&xas, NULL);
> + mapping->nrpages -= 1UL << dax_entry_order(entry);
> + ret = 1;
> +out:
> + put_unlocked_entry(&xas, entry, WAKE_ALL);
> + xas_unlock_irq(&xas);
> + return ret;
> +}
> +
> +int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
> + pgoff_t index)
> +{
> + return __dax_invalidate_entry(mapping, index, false);
> +}
> +
> +/*
> + * Delete DAX entry at @index from @mapping. Wait for it
> + * to be unlocked before deleting it.
> + */
> +int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
> +{
> + int ret = __dax_invalidate_entry(mapping, index, true);
> +
> + /*
> + * This gets called from truncate / punch_hole path. As such, the caller
> + * must hold locks protecting against concurrent modifications of the
> + * page cache (usually fs-private i_mmap_sem for writing). Since the
> + * caller has seen a DAX entry for this index, we better find it
> + * at that index as well...
> + */
> + WARN_ON_ONCE(!ret);
> + return ret;
> +}
> +
> +/*
> + * By this point dax_grab_mapping_entry() has ensured that we have a locked entry
> + * of the appropriate size so we don't have to worry about downgrading PMDs to
> + * PTEs. If we happen to be trying to insert a PTE and there is a PMD
> + * already in the tree, we will skip the insertion and just dirty the PMD as
> + * appropriate.
> + */
> +vm_fault_t dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> + void **pentry, pfn_t pfn, unsigned long flags)
> +{
> + struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> + void *new_entry = dax_make_entry(pfn, flags);
> + bool dirty = flags & DAX_DIRTY;
> + bool cow = flags & DAX_COW;
> + void *entry = *pentry;
> +
> + if (dirty)
> + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> + if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
> + unsigned long index = xas->xa_index;
> + /* we are replacing a zero page with block mapping */
> + if (dax_is_pmd_entry(entry))
> + unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
> + PG_PMD_NR, false);
> + else /* pte entry */
> + unmap_mapping_pages(mapping, index, 1, false);
> + }
> +
> + xas_reset(xas);
> + xas_lock_irq(xas);
> + if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> + void *old;
> +
> + dax_disassociate_entry(entry, mapping, false);
> + dax_associate_entry(new_entry, mapping, vmf, flags);
> + /*
> + * Only swap our new entry into the page cache if the current
> + * entry is a zero page or an empty entry. If a normal PTE or
> + * PMD entry is already in the cache, we leave it alone. This
> + * means that if we are trying to insert a PTE and the
> + * existing entry is a PMD, we will just leave the PMD in the
> + * tree and dirty it if necessary.
> + */
> + old = dax_lock_entry(xas, new_entry);
> + WARN_ON_ONCE(old !=
> + xa_mk_value(xa_to_value(entry) | DAX_LOCKED));
> + entry = new_entry;
> + } else {
> + xas_load(xas); /* Walk the xa_state */
> + }
> +
> + if (dirty)
> + xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
> +
> + if (cow)
> + xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
> +
> + xas_unlock_irq(xas);
> + *pentry = entry;
> + return 0;
> +}
> +
> +int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
> + struct address_space *mapping, void *entry)
> +{
> + unsigned long pfn, index, count, end;
> + long ret = 0;
> + struct vm_area_struct *vma;
> +
> + /*
> + * A page got tagged dirty in DAX mapping? Something is seriously
> + * wrong.
> + */
> + if (WARN_ON(!xa_is_value(entry)))
> + return -EIO;
> +
> + if (unlikely(dax_is_locked(entry))) {
> + void *old_entry = entry;
> +
> + entry = get_unlocked_entry(xas, 0);
> +
> + /* Entry got punched out / reallocated? */
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + goto put_unlocked;
> + /*
> + * Entry got reallocated elsewhere? No need to writeback.
> + * We have to compare pfns as we must not bail out due to
> + * difference in lockbit or entry type.
> + */
> + if (dax_to_pfn(old_entry) != dax_to_pfn(entry))
> + goto put_unlocked;
> + if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
> + dax_is_zero_entry(entry))) {
> + ret = -EIO;
> + goto put_unlocked;
> + }
> +
> + /* Another fsync thread may have already done this entry */
> + if (!xas_get_mark(xas, PAGECACHE_TAG_TOWRITE))
> + goto put_unlocked;
> + }
> +
> + /* Lock the entry to serialize with page faults */
> + dax_lock_entry(xas, entry);
> +
> + /*
> + * We can clear the tag now but we have to be careful so that concurrent
> + * dax_writeback_one() calls for the same index cannot finish before we
> + * actually flush the caches. This is achieved as the calls will look
> + * at the entry only under the i_pages lock and once they do that
> + * they will see the entry locked and wait for it to unlock.
> + */
> + xas_clear_mark(xas, PAGECACHE_TAG_TOWRITE);
> + xas_unlock_irq(xas);
> +
> + /*
> + * If dax_writeback_mapping_range() was given a wbc->range_start
> + * in the middle of a PMD, the 'index' we use needs to be
> + * aligned to the start of the PMD.
> + * This allows us to flush for PMD_SIZE and not have to worry about
> + * partial PMD writebacks.
> + */
> + pfn = dax_to_pfn(entry);
> + count = 1UL << dax_entry_order(entry);
> + index = xas->xa_index & ~(count - 1);
> + end = index + count - 1;
> +
> + /* Walk all mappings of a given index of a file and writeprotect them */
> + i_mmap_lock_read(mapping);
> + vma_interval_tree_foreach(vma, &mapping->i_mmap, index, end) {
> + pfn_mkclean_range(pfn, count, index, vma);
> + cond_resched();
> + }
> + i_mmap_unlock_read(mapping);
> +
> + dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
> + /*
> + * After we have flushed the cache, we can clear the dirty tag. There
> + * cannot be new dirty data in the pfn after the flush has completed as
> + * the pfn mappings are writeprotected and fault waits for mapping
> + * entry lock.
> + */
> + xas_reset(xas);
> + xas_lock_irq(xas);
> + xas_store(xas, entry);
> + xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
> + dax_wake_entry(xas, entry, WAKE_NEXT);
> +
> + trace_dax_writeback_one(mapping->host, index, count);
> + return ret;
> +
> + put_unlocked:
> + put_unlocked_entry(xas, entry, WAKE_NEXT);
> + return ret;
> +}
> +
> +/*
> + * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
> + * @vmf: The description of the fault
> + * @pfn: PFN to insert
> + * @order: Order of entry to insert.
> + *
> + * This function inserts a writeable PTE or PMD entry into the page tables
> + * for an mmaped DAX file. It also marks the page cache entry as dirty.
> + */
> +vm_fault_t dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn,
> + unsigned int order)
> +{
> + struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> + XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, order);
> + void *entry;
> + vm_fault_t ret;
> +
> + xas_lock_irq(&xas);
> + entry = get_unlocked_entry(&xas, order);
> + /* Did we race with someone splitting entry or so? */
> + if (!entry || dax_is_conflict(entry) ||
> + (order == 0 && !dax_is_pte_entry(entry))) {
> + put_unlocked_entry(&xas, entry, WAKE_NEXT);
> + xas_unlock_irq(&xas);
> + trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
> + VM_FAULT_NOPAGE);
> + return VM_FAULT_NOPAGE;
> + }
> + xas_set_mark(&xas, PAGECACHE_TAG_DIRTY);
> + dax_lock_entry(&xas, entry);
> + xas_unlock_irq(&xas);
> + if (order == 0)
> + ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
> +#ifdef CONFIG_FS_DAX_PMD
> + else if (order == PMD_ORDER)
> + ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE);
> +#endif
> + else
> + ret = VM_FAULT_FALLBACK;
> + dax_unlock_entry(&xas, entry);
> + trace_dax_insert_pfn_mkwrite(mapping->host, vmf, ret);
> + return ret;
> +}
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 4909ad945a49..0976857ec7f2 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -564,6 +564,8 @@ static int __init dax_core_init(void)
> if (rc)
> return rc;
>
> + dax_mapping_init();
> +
> rc = alloc_chrdev_region(&dax_devt, 0, MINORMASK+1, "dax");
> if (rc)
> goto err_chrdev;
> @@ -590,5 +592,5 @@ static void __exit dax_core_exit(void)
>
> MODULE_AUTHOR("Intel Corporation");
> MODULE_LICENSE("GPL v2");
> -subsys_initcall(dax_core_init);
> +fs_initcall(dax_core_init);
> module_exit(dax_core_exit);
> diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
> index 5a29046e3319..3bb17448d1c8 100644
> --- a/drivers/nvdimm/Kconfig
> +++ b/drivers/nvdimm/Kconfig
> @@ -78,6 +78,7 @@ config NVDIMM_DAX
> bool "NVDIMM DAX: Raw access to persistent memory"
> default LIBNVDIMM
> depends on NVDIMM_PFN
> + depends on DAX
> help
> Support raw device dax access to a persistent memory
> namespace. For environments that want to hard partition
> diff --git a/fs/dax.c b/fs/dax.c
> index ee2568c8b135..79e49e718d33 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -27,847 +27,8 @@
> #include <linux/rmap.h>
> #include <asm/pgalloc.h>
>
> -#define CREATE_TRACE_POINTS
> #include <trace/events/fs_dax.h>
>
> -static inline unsigned int pe_order(enum page_entry_size pe_size)
> -{
> - if (pe_size == PE_SIZE_PTE)
> - return PAGE_SHIFT - PAGE_SHIFT;
> - if (pe_size == PE_SIZE_PMD)
> - return PMD_SHIFT - PAGE_SHIFT;
> - if (pe_size == PE_SIZE_PUD)
> - return PUD_SHIFT - PAGE_SHIFT;
> - return ~0;
> -}
> -
> -/* We choose 4096 entries - same as per-zone page wait tables */
> -#define DAX_WAIT_TABLE_BITS 12
> -#define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
> -
> -/* The 'colour' (ie low bits) within a PMD of a page offset. */
> -#define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
> -#define PG_PMD_NR (PMD_SIZE >> PAGE_SHIFT)
> -
> -/* The order of a PMD entry */
> -#define PMD_ORDER (PMD_SHIFT - PAGE_SHIFT)
> -
> -static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
> -
> -static int __init init_dax_wait_table(void)
> -{
> - int i;
> -
> - for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
> - init_waitqueue_head(wait_table + i);
> - return 0;
> -}
> -fs_initcall(init_dax_wait_table);
> -
> -/*
> - * DAX pagecache entries use XArray value entries so they can't be mistaken
> - * for pages. We use one bit for locking, one bit for the entry size (PMD)
> - * and two more to tell us if the entry is a zero page or an empty entry that
> - * is just used for locking. In total four special bits.
> - *
> - * If the PMD bit isn't set the entry has size PAGE_SIZE, and if the ZERO_PAGE
> - * and EMPTY bits aren't set the entry is a normal DAX entry with a filesystem
> - * block allocation.
> - */
> -#define DAX_SHIFT (5)
> -#define DAX_MASK ((1UL << DAX_SHIFT) - 1)
> -#define DAX_LOCKED (1UL << 0)
> -#define DAX_PMD (1UL << 1)
> -#define DAX_ZERO_PAGE (1UL << 2)
> -#define DAX_EMPTY (1UL << 3)
> -#define DAX_ZAP (1UL << 4)
> -
> -/*
> - * These flags are not conveyed in Xarray value entries, they are just
> - * modifiers to dax_insert_entry().
> - */
> -#define DAX_DIRTY (1UL << (DAX_SHIFT + 0))
> -#define DAX_COW (1UL << (DAX_SHIFT + 1))
> -
> -static unsigned long dax_to_pfn(void *entry)
> -{
> - return xa_to_value(entry) >> DAX_SHIFT;
> -}
> -
> -static void *dax_make_entry(pfn_t pfn, unsigned long flags)
> -{
> - return xa_mk_value((flags & DAX_MASK) |
> - (pfn_t_to_pfn(pfn) << DAX_SHIFT));
> -}
> -
> -static bool dax_is_locked(void *entry)
> -{
> - return xa_to_value(entry) & DAX_LOCKED;
> -}
> -
> -static bool dax_is_zapped(void *entry)
> -{
> - return xa_to_value(entry) & DAX_ZAP;
> -}
> -
> -static unsigned int dax_entry_order(void *entry)
> -{
> - if (xa_to_value(entry) & DAX_PMD)
> - return PMD_ORDER;
> - return 0;
> -}
> -
> -static unsigned long dax_is_pmd_entry(void *entry)
> -{
> - return xa_to_value(entry) & DAX_PMD;
> -}
> -
> -static bool dax_is_pte_entry(void *entry)
> -{
> - return !(xa_to_value(entry) & DAX_PMD);
> -}
> -
> -static int dax_is_zero_entry(void *entry)
> -{
> - return xa_to_value(entry) & DAX_ZERO_PAGE;
> -}
> -
> -static int dax_is_empty_entry(void *entry)
> -{
> - return xa_to_value(entry) & DAX_EMPTY;
> -}
> -
> -/*
> - * true if the entry that was found is of a smaller order than the entry
> - * we were looking for
> - */
> -static bool dax_is_conflict(void *entry)
> -{
> - return entry == XA_RETRY_ENTRY;
> -}
> -
> -/*
> - * DAX page cache entry locking
> - */
> -struct exceptional_entry_key {
> - struct xarray *xa;
> - pgoff_t entry_start;
> -};
> -
> -struct wait_exceptional_entry_queue {
> - wait_queue_entry_t wait;
> - struct exceptional_entry_key key;
> -};
> -
> -/**
> - * enum dax_wake_mode: waitqueue wakeup behaviour
> - * @WAKE_ALL: wake all waiters in the waitqueue
> - * @WAKE_NEXT: wake only the first waiter in the waitqueue
> - */
> -enum dax_wake_mode {
> - WAKE_ALL,
> - WAKE_NEXT,
> -};
> -
> -static wait_queue_head_t *dax_entry_waitqueue(struct xa_state *xas,
> - void *entry, struct exceptional_entry_key *key)
> -{
> - unsigned long hash;
> - unsigned long index = xas->xa_index;
> -
> - /*
> - * If 'entry' is a PMD, align the 'index' that we use for the wait
> - * queue to the start of that PMD. This ensures that all offsets in
> - * the range covered by the PMD map to the same bit lock.
> - */
> - if (dax_is_pmd_entry(entry))
> - index &= ~PG_PMD_COLOUR;
> - key->xa = xas->xa;
> - key->entry_start = index;
> -
> - hash = hash_long((unsigned long)xas->xa ^ index, DAX_WAIT_TABLE_BITS);
> - return wait_table + hash;
> -}
> -
> -static int wake_exceptional_entry_func(wait_queue_entry_t *wait,
> - unsigned int mode, int sync, void *keyp)
> -{
> - struct exceptional_entry_key *key = keyp;
> - struct wait_exceptional_entry_queue *ewait =
> - container_of(wait, struct wait_exceptional_entry_queue, wait);
> -
> - if (key->xa != ewait->key.xa ||
> - key->entry_start != ewait->key.entry_start)
> - return 0;
> - return autoremove_wake_function(wait, mode, sync, NULL);
> -}
> -
> -/*
> - * @entry may no longer be the entry at the index in the mapping.
> - * The important information it's conveying is whether the entry at
> - * this index used to be a PMD entry.
> - */
> -static void dax_wake_entry(struct xa_state *xas, void *entry,
> - enum dax_wake_mode mode)
> -{
> - struct exceptional_entry_key key;
> - wait_queue_head_t *wq;
> -
> - wq = dax_entry_waitqueue(xas, entry, &key);
> -
> - /*
> - * Checking for locked entry and prepare_to_wait_exclusive() happens
> - * under the i_pages lock, ditto for entry handling in our callers.
> - * So at this point all tasks that could have seen our entry locked
> - * must be in the waitqueue and the following check will see them.
> - */
> - if (waitqueue_active(wq))
> - __wake_up(wq, TASK_NORMAL, mode == WAKE_ALL ? 0 : 1, &key);
> -}
> -
> -/*
> - * Look up entry in page cache, wait for it to become unlocked if it
> - * is a DAX entry and return it. The caller must subsequently call
> - * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry()
> - * if it did. The entry returned may have a larger order than @order.
> - * If @order is larger than the order of the entry found in i_pages, this
> - * function returns a dax_is_conflict entry.
> - *
> - * Must be called with the i_pages lock held.
> - */
> -static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
> -{
> - void *entry;
> - struct wait_exceptional_entry_queue ewait;
> - wait_queue_head_t *wq;
> -
> - init_wait(&ewait.wait);
> - ewait.wait.func = wake_exceptional_entry_func;
> -
> - for (;;) {
> - entry = xas_find_conflict(xas);
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> - return entry;
> - if (dax_entry_order(entry) < order)
> - return XA_RETRY_ENTRY;
> - if (!dax_is_locked(entry))
> - return entry;
> -
> - wq = dax_entry_waitqueue(xas, entry, &ewait.key);
> - prepare_to_wait_exclusive(wq, &ewait.wait,
> - TASK_UNINTERRUPTIBLE);
> - xas_unlock_irq(xas);
> - xas_reset(xas);
> - schedule();
> - finish_wait(wq, &ewait.wait);
> - xas_lock_irq(xas);
> - }
> -}
> -
> -/*
> - * The only thing keeping the address space around is the i_pages lock
> - * (it's cycled in clear_inode() after removing the entries from i_pages)
> - * After we call xas_unlock_irq(), we cannot touch xas->xa.
> - */
> -static void wait_entry_unlocked(struct xa_state *xas, void *entry)
> -{
> - struct wait_exceptional_entry_queue ewait;
> - wait_queue_head_t *wq;
> -
> - init_wait(&ewait.wait);
> - ewait.wait.func = wake_exceptional_entry_func;
> -
> - wq = dax_entry_waitqueue(xas, entry, &ewait.key);
> - /*
> - * Unlike get_unlocked_entry() there is no guarantee that this
> - * path ever successfully retrieves an unlocked entry before an
> - * inode dies. Perform a non-exclusive wait in case this path
> - * never successfully performs its own wake up.
> - */
> - prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
> - xas_unlock_irq(xas);
> - schedule();
> - finish_wait(wq, &ewait.wait);
> -}
> -
> -static void put_unlocked_entry(struct xa_state *xas, void *entry,
> - enum dax_wake_mode mode)
> -{
> - if (entry && !dax_is_conflict(entry))
> - dax_wake_entry(xas, entry, mode);
> -}
> -
> -/*
> - * We used the xa_state to get the entry, but then we locked the entry and
> - * dropped the xa_lock, so we know the xa_state is stale and must be reset
> - * before use.
> - */
> -static void dax_unlock_entry(struct xa_state *xas, void *entry)
> -{
> - void *old;
> -
> - BUG_ON(dax_is_locked(entry));
> - xas_reset(xas);
> - xas_lock_irq(xas);
> - old = xas_store(xas, entry);
> - xas_unlock_irq(xas);
> - BUG_ON(!dax_is_locked(old));
> - dax_wake_entry(xas, entry, WAKE_NEXT);
> -}
> -
> -/*
> - * Return: The entry stored at this location before it was locked.
> - */
> -static void *dax_lock_entry(struct xa_state *xas, void *entry)
> -{
> - unsigned long v = xa_to_value(entry);
> - return xas_store(xas, xa_mk_value(v | DAX_LOCKED));
> -}
> -
> -static unsigned long dax_entry_size(void *entry)
> -{
> - if (dax_is_zero_entry(entry))
> - return 0;
> - else if (dax_is_empty_entry(entry))
> - return 0;
> - else if (dax_is_pmd_entry(entry))
> - return PMD_SIZE;
> - else
> - return PAGE_SIZE;
> -}
> -
> -static unsigned long dax_end_pfn(void *entry)
> -{
> - return dax_to_pfn(entry) + dax_entry_size(entry) / PAGE_SIZE;
> -}
> -
> -/*
> - * Iterate through all mapped pfns represented by an entry, i.e. skip
> - * 'empty' and 'zero' entries.
> - */
> -#define for_each_mapped_pfn(entry, pfn) \
> - for (pfn = dax_to_pfn(entry); \
> - pfn < dax_end_pfn(entry); pfn++)
> -
> -static inline bool dax_mapping_is_cow(struct address_space *mapping)
> -{
> - return (unsigned long)mapping == PAGE_MAPPING_DAX_COW;
> -}
> -
> -/*
> - * Set the page->mapping with FS_DAX_MAPPING_COW flag, increase the refcount.
> - */
> -static inline void dax_mapping_set_cow(struct page *page)
> -{
> - if ((uintptr_t)page->mapping != PAGE_MAPPING_DAX_COW) {
> - /*
> - * Reset the index if the page was already mapped
> - * regularly before.
> - */
> - if (page->mapping)
> - page->index = 1;
> - page->mapping = (void *)PAGE_MAPPING_DAX_COW;
> - }
> - page->index++;
> -}
> -
> -/*
> - * When it is called in dax_insert_entry(), the cow flag will indicate that
> - * whether this entry is shared by multiple files. If so, set the page->mapping
> - * FS_DAX_MAPPING_COW, and use page->index as refcount.
> - */
> -static vm_fault_t dax_associate_entry(void *entry,
> - struct address_space *mapping,
> - struct vm_fault *vmf, unsigned long flags)
> -{
> - unsigned long size = dax_entry_size(entry), pfn, index;
> - struct dev_pagemap *pgmap;
> - int i = 0;
> -
> - if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> - return 0;
> -
> - if (!size)
> - return 0;
> -
> - if (!(flags & DAX_COW)) {
> - pfn = dax_to_pfn(entry);
> - pgmap = get_dev_pagemap_many(pfn, NULL, PHYS_PFN(size));
> - if (!pgmap)
> - return VM_FAULT_SIGBUS;
> - }
> -
> - index = linear_page_index(vmf->vma, ALIGN(vmf->address, size));
> - for_each_mapped_pfn(entry, pfn) {
> - struct page *page = pfn_to_page(pfn);
> -
> - if (flags & DAX_COW) {
> - dax_mapping_set_cow(page);
> - } else {
> - WARN_ON_ONCE(page->mapping);
> - page->mapping = mapping;
> - page->index = index + i++;
> - page_ref_inc(page);
> - }
> - }
> -
> - return 0;
> -}
> -
> -static void dax_disassociate_entry(void *entry, struct address_space *mapping,
> - bool trunc)
> -{
> - unsigned long size = dax_entry_size(entry), pfn;
> - struct page *page;
> -
> - if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> - return;
> -
> - if (!size)
> - return;
> -
> - for_each_mapped_pfn(entry, pfn) {
> - page = pfn_to_page(pfn);
> - if (dax_mapping_is_cow(page->mapping)) {
> - /* keep the CoW flag if this page is still shared */
> - if (page->index-- > 0)
> - continue;
> - } else {
> - WARN_ON_ONCE(trunc && !dax_is_zapped(entry));
> - WARN_ON_ONCE(trunc && !dax_page_idle(page));
> - WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> - }
> - page->mapping = NULL;
> - page->index = 0;
> - }
> -
> - if (trunc && !dax_mapping_is_cow(page->mapping)) {
> - page = pfn_to_page(dax_to_pfn(entry));
> - put_dev_pagemap_many(page->pgmap, PHYS_PFN(size));
> - }
> -}
> -
> -/*
> - * dax_lock_page - Lock the DAX entry corresponding to a page
> - * @page: The page whose entry we want to lock
> - *
> - * Context: Process context.
> - * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could
> - * not be locked.
> - */
> -dax_entry_t dax_lock_page(struct page *page)
> -{
> - XA_STATE(xas, NULL, 0);
> - void *entry;
> -
> - /* Ensure page->mapping isn't freed while we look at it */
> - rcu_read_lock();
> - for (;;) {
> - struct address_space *mapping = READ_ONCE(page->mapping);
> -
> - entry = NULL;
> - if (!mapping || !dax_mapping(mapping))
> - break;
> -
> - /*
> - * In the device-dax case there's no need to lock, a
> - * struct dev_pagemap pin is sufficient to keep the
> - * inode alive, and we assume we have dev_pagemap pin
> - * otherwise we would not have a valid pfn_to_page()
> - * translation.
> - */
> - entry = (void *)~0UL;
> - if (S_ISCHR(mapping->host->i_mode))
> - break;
> -
> - xas.xa = &mapping->i_pages;
> - xas_lock_irq(&xas);
> - if (mapping != page->mapping) {
> - xas_unlock_irq(&xas);
> - continue;
> - }
> - xas_set(&xas, page->index);
> - entry = xas_load(&xas);
> - if (dax_is_locked(entry)) {
> - rcu_read_unlock();
> - wait_entry_unlocked(&xas, entry);
> - rcu_read_lock();
> - continue;
> - }
> - dax_lock_entry(&xas, entry);
> - xas_unlock_irq(&xas);
> - break;
> - }
> - rcu_read_unlock();
> - return (dax_entry_t)entry;
> -}
> -
> -void dax_unlock_page(struct page *page, dax_entry_t cookie)
> -{
> - struct address_space *mapping = page->mapping;
> - XA_STATE(xas, &mapping->i_pages, page->index);
> -
> - if (S_ISCHR(mapping->host->i_mode))
> - return;
> -
> - dax_unlock_entry(&xas, (void *)cookie);
> -}
> -
> -/*
> - * dax_lock_mapping_entry - Lock the DAX entry corresponding to a mapping
> - * @mapping: the file's mapping whose entry we want to lock
> - * @index: the offset within this file
> - * @page: output the dax page corresponding to this dax entry
> - *
> - * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the entry
> - * could not be locked.
> - */
> -dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, pgoff_t index,
> - struct page **page)
> -{
> - XA_STATE(xas, NULL, 0);
> - void *entry;
> -
> - rcu_read_lock();
> - for (;;) {
> - entry = NULL;
> - if (!dax_mapping(mapping))
> - break;
> -
> - xas.xa = &mapping->i_pages;
> - xas_lock_irq(&xas);
> - xas_set(&xas, index);
> - entry = xas_load(&xas);
> - if (dax_is_locked(entry)) {
> - rcu_read_unlock();
> - wait_entry_unlocked(&xas, entry);
> - rcu_read_lock();
> - continue;
> - }
> - if (!entry ||
> - dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> - /*
> - * Because we are looking for entry from file's mapping
> - * and index, so the entry may not be inserted for now,
> - * or even a zero/empty entry. We don't think this is
> - * an error case. So, return a special value and do
> - * not output @page.
> - */
> - entry = (void *)~0UL;
> - } else {
> - *page = pfn_to_page(dax_to_pfn(entry));
> - dax_lock_entry(&xas, entry);
> - }
> - xas_unlock_irq(&xas);
> - break;
> - }
> - rcu_read_unlock();
> - return (dax_entry_t)entry;
> -}
> -
> -void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index,
> - dax_entry_t cookie)
> -{
> - XA_STATE(xas, &mapping->i_pages, index);
> -
> - if (cookie == ~0UL)
> - return;
> -
> - dax_unlock_entry(&xas, (void *)cookie);
> -}
> -
> -/*
> - * Find page cache entry at given index. If it is a DAX entry, return it
> - * with the entry locked. If the page cache doesn't contain an entry at
> - * that index, add a locked empty entry.
> - *
> - * When requesting an entry with size DAX_PMD, grab_mapping_entry() will
> - * either return that locked entry or will return VM_FAULT_FALLBACK.
> - * This will happen if there are any PTE entries within the PMD range
> - * that we are requesting.
> - *
> - * We always favor PTE entries over PMD entries. There isn't a flow where we
> - * evict PTE entries in order to 'upgrade' them to a PMD entry. A PMD
> - * insertion will fail if it finds any PTE entries already in the tree, and a
> - * PTE insertion will cause an existing PMD entry to be unmapped and
> - * downgraded to PTE entries. This happens for both PMD zero pages as
> - * well as PMD empty entries.
> - *
> - * The exception to this downgrade path is for PMD entries that have
> - * real storage backing them. We will leave these real PMD entries in
> - * the tree, and PTE writes will simply dirty the entire PMD entry.
> - *
> - * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
> - * persistent memory the benefit is doubtful. We can add that later if we can
> - * show it helps.
> - *
> - * On error, this function does not return an ERR_PTR. Instead it returns
> - * a VM_FAULT code, encoded as an xarray internal entry. The ERR_PTR values
> - * overlap with xarray value entries.
> - */
> -static void *grab_mapping_entry(struct xa_state *xas,
> - struct address_space *mapping, unsigned int order)
> -{
> - unsigned long index = xas->xa_index;
> - bool pmd_downgrade; /* splitting PMD entry into PTE entries? */
> - void *entry;
> -
> -retry:
> - pmd_downgrade = false;
> - xas_lock_irq(xas);
> - entry = get_unlocked_entry(xas, order);
> -
> - if (entry) {
> - if (dax_is_conflict(entry))
> - goto fallback;
> - if (!xa_is_value(entry)) {
> - xas_set_err(xas, -EIO);
> - goto out_unlock;
> - }
> -
> - if (order == 0) {
> - if (dax_is_pmd_entry(entry) &&
> - (dax_is_zero_entry(entry) ||
> - dax_is_empty_entry(entry))) {
> - pmd_downgrade = true;
> - }
> - }
> - }
> -
> - if (pmd_downgrade) {
> - /*
> - * Make sure 'entry' remains valid while we drop
> - * the i_pages lock.
> - */
> - dax_lock_entry(xas, entry);
> -
> - /*
> - * Besides huge zero pages the only other thing that gets
> - * downgraded are empty entries which don't need to be
> - * unmapped.
> - */
> - if (dax_is_zero_entry(entry)) {
> - xas_unlock_irq(xas);
> - unmap_mapping_pages(mapping,
> - xas->xa_index & ~PG_PMD_COLOUR,
> - PG_PMD_NR, false);
> - xas_reset(xas);
> - xas_lock_irq(xas);
> - }
> -
> - dax_disassociate_entry(entry, mapping, false);
> - xas_store(xas, NULL); /* undo the PMD join */
> - dax_wake_entry(xas, entry, WAKE_ALL);
> - mapping->nrpages -= PG_PMD_NR;
> - entry = NULL;
> - xas_set(xas, index);
> - }
> -
> - if (entry) {
> - dax_lock_entry(xas, entry);
> - } else {
> - unsigned long flags = DAX_EMPTY;
> -
> - if (order > 0)
> - flags |= DAX_PMD;
> - entry = dax_make_entry(pfn_to_pfn_t(0), flags);
> - dax_lock_entry(xas, entry);
> - if (xas_error(xas))
> - goto out_unlock;
> - mapping->nrpages += 1UL << order;
> - }
> -
> -out_unlock:
> - xas_unlock_irq(xas);
> - if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
> - goto retry;
> - if (xas->xa_node == XA_ERROR(-ENOMEM))
> - return xa_mk_internal(VM_FAULT_OOM);
> - if (xas_error(xas))
> - return xa_mk_internal(VM_FAULT_SIGBUS);
> - return entry;
> -fallback:
> - xas_unlock_irq(xas);
> - return xa_mk_internal(VM_FAULT_FALLBACK);
> -}
> -
> -static void *dax_zap_entry(struct xa_state *xas, void *entry)
> -{
> - unsigned long v = xa_to_value(entry);
> -
> - return xas_store(xas, xa_mk_value(v | DAX_ZAP));
> -}
> -
> -/**
> - * Return NULL if the entry is zapped and all pages in the entry are
> - * idle, otherwise return the non-idle page in the entry
> - */
> -static struct page *dax_zap_pages(struct xa_state *xas, void *entry)
> -{
> - struct page *ret = NULL;
> - unsigned long pfn;
> - bool zap;
> -
> - if (!dax_entry_size(entry))
> - return NULL;
> -
> - zap = !dax_is_zapped(entry);
> -
> - for_each_mapped_pfn(entry, pfn) {
> - struct page *page = pfn_to_page(pfn);
> -
> - if (zap)
> - page_ref_dec(page);
> -
> - if (!ret && !dax_page_idle(page))
> - ret = page;
> - }
> -
> - if (zap)
> - dax_zap_entry(xas, entry);
> -
> - return ret;
> -}
> -
> -/**
> - * dax_zap_mappings_range - find first pinned page in @mapping
> - * @mapping: address space to scan for a page with ref count > 1
> - * @start: Starting offset. Page containing 'start' is included.
> - * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
> - * pages from 'start' till the end of file are included.
> - *
> - * DAX requires ZONE_DEVICE mapped pages. These pages are never
> - * 'onlined' to the page allocator so they are considered idle when
> - * page->count == 1. A filesystem uses this interface to determine if
> - * any page in the mapping is busy, i.e. for DMA, or other
> - * get_user_pages() usages.
> - *
> - * It is expected that the filesystem is holding locks to block the
> - * establishment of new mappings in this address_space. I.e. it expects
> - * to be able to run unmap_mapping_range() and subsequently not race
> - * mapping_mapped() becoming true.
> - */
> -struct page *dax_zap_mappings_range(struct address_space *mapping, loff_t start,
> - loff_t end)
> -{
> - void *entry;
> - unsigned int scanned = 0;
> - struct page *page = NULL;
> - pgoff_t start_idx = start >> PAGE_SHIFT;
> - pgoff_t end_idx;
> - XA_STATE(xas, &mapping->i_pages, start_idx);
> -
> - /*
> - * In the 'limited' case get_user_pages() for dax is disabled.
> - */
> - if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> - return NULL;
> -
> - if (!dax_mapping(mapping))
> - return NULL;
> -
> - /* If end == LLONG_MAX, all pages from start to till end of file */
> - if (end == LLONG_MAX)
> - end_idx = ULONG_MAX;
> - else
> - end_idx = end >> PAGE_SHIFT;
> - /*
> - * If we race get_user_pages_fast() here either we'll see the
> - * elevated page count in the iteration and wait, or
> - * get_user_pages_fast() will see that the page it took a reference
> - * against is no longer mapped in the page tables and bail to the
> - * get_user_pages() slow path. The slow path is protected by
> - * pte_lock() and pmd_lock(). New references are not taken without
> - * holding those locks, and unmap_mapping_pages() will not zero the
> - * pte or pmd without holding the respective lock, so we are
> - * guaranteed to either see new references or prevent new
> - * references from being established.
> - */
> - unmap_mapping_pages(mapping, start_idx, end_idx - start_idx + 1, 0);
> -
> - xas_lock_irq(&xas);
> - xas_for_each(&xas, entry, end_idx) {
> - if (WARN_ON_ONCE(!xa_is_value(entry)))
> - continue;
> - if (unlikely(dax_is_locked(entry)))
> - entry = get_unlocked_entry(&xas, 0);
> - if (entry)
> - page = dax_zap_pages(&xas, entry);
> - put_unlocked_entry(&xas, entry, WAKE_NEXT);
> - if (page)
> - break;
> - if (++scanned % XA_CHECK_SCHED)
> - continue;
> -
> - xas_pause(&xas);
> - xas_unlock_irq(&xas);
> - cond_resched();
> - xas_lock_irq(&xas);
> - }
> - xas_unlock_irq(&xas);
> - return page;
> -}
> -EXPORT_SYMBOL_GPL(dax_zap_mappings_range);
> -
> -struct page *dax_zap_mappings(struct address_space *mapping)
> -{
> - return dax_zap_mappings_range(mapping, 0, LLONG_MAX);
> -}
> -EXPORT_SYMBOL_GPL(dax_zap_mappings);
> -
> -static int __dax_invalidate_entry(struct address_space *mapping,
> - pgoff_t index, bool trunc)
> -{
> - XA_STATE(xas, &mapping->i_pages, index);
> - int ret = 0;
> - void *entry;
> -
> - xas_lock_irq(&xas);
> - entry = get_unlocked_entry(&xas, 0);
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> - goto out;
> - if (!trunc &&
> - (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) ||
> - xas_get_mark(&xas, PAGECACHE_TAG_TOWRITE)))
> - goto out;
> - dax_disassociate_entry(entry, mapping, trunc);
> - xas_store(&xas, NULL);
> - mapping->nrpages -= 1UL << dax_entry_order(entry);
> - ret = 1;
> -out:
> - put_unlocked_entry(&xas, entry, WAKE_ALL);
> - xas_unlock_irq(&xas);
> - return ret;
> -}
> -
> -/*
> - * Delete DAX entry at @index from @mapping. Wait for it
> - * to be unlocked before deleting it.
> - */
> -int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
> -{
> - int ret = __dax_invalidate_entry(mapping, index, true);
> -
> - /*
> - * This gets called from truncate / punch_hole path. As such, the caller
> - * must hold locks protecting against concurrent modifications of the
> - * page cache (usually fs-private i_mmap_sem for writing). Since the
> - * caller has seen a DAX entry for this index, we better find it
> - * at that index as well...
> - */
> - WARN_ON_ONCE(!ret);
> - return ret;
> -}
> -
> -/*
> - * Invalidate DAX entry if it is clean.
> - */
> -int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
> - pgoff_t index)
> -{
> - return __dax_invalidate_entry(mapping, index, false);
> -}
> -
> static pgoff_t dax_iomap_pgoff(const struct iomap *iomap, loff_t pos)
> {
> return PHYS_PFN(iomap->addr + (pos & PAGE_MASK) - iomap->offset);
> @@ -894,195 +55,6 @@ static int copy_cow_page_dax(struct vm_fault *vmf, const struct iomap_iter *iter
> return 0;
> }
>
> -/*
> - * MAP_SYNC on a dax mapping guarantees dirty metadata is
> - * flushed on write-faults (non-cow), but not read-faults.
> - */
> -static bool dax_fault_is_synchronous(const struct iomap_iter *iter,
> - struct vm_area_struct *vma)
> -{
> - return (iter->flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC) &&
> - (iter->iomap.flags & IOMAP_F_DIRTY);
> -}
> -
> -static bool dax_fault_is_cow(const struct iomap_iter *iter)
> -{
> - return (iter->flags & IOMAP_WRITE) &&
> - (iter->iomap.flags & IOMAP_F_SHARED);
> -}
> -
> -static unsigned long dax_iter_flags(const struct iomap_iter *iter,
> - struct vm_fault *vmf)
> -{
> - unsigned long flags = 0;
> -
> - if (!dax_fault_is_synchronous(iter, vmf->vma))
> - flags |= DAX_DIRTY;
> -
> - if (dax_fault_is_cow(iter))
> - flags |= DAX_COW;
> -
> - return flags;
> -}
> -
> -/*
> - * By this point grab_mapping_entry() has ensured that we have a locked entry
> - * of the appropriate size so we don't have to worry about downgrading PMDs to
> - * PTEs. If we happen to be trying to insert a PTE and there is a PMD
> - * already in the tree, we will skip the insertion and just dirty the PMD as
> - * appropriate.
> - */
> -static vm_fault_t dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> - void **pentry, pfn_t pfn,
> - unsigned long flags)
> -{
> - struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> - void *new_entry = dax_make_entry(pfn, flags);
> - bool dirty = flags & DAX_DIRTY;
> - bool cow = flags & DAX_COW;
> - void *entry = *pentry;
> -
> - if (dirty)
> - __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> -
> - if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
> - unsigned long index = xas->xa_index;
> - /* we are replacing a zero page with block mapping */
> - if (dax_is_pmd_entry(entry))
> - unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
> - PG_PMD_NR, false);
> - else /* pte entry */
> - unmap_mapping_pages(mapping, index, 1, false);
> - }
> -
> - xas_reset(xas);
> - xas_lock_irq(xas);
> - if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
> - void *old;
> -
> - dax_disassociate_entry(entry, mapping, false);
> - dax_associate_entry(new_entry, mapping, vmf, flags);
> - /*
> - * Only swap our new entry into the page cache if the current
> - * entry is a zero page or an empty entry. If a normal PTE or
> - * PMD entry is already in the cache, we leave it alone. This
> - * means that if we are trying to insert a PTE and the
> - * existing entry is a PMD, we will just leave the PMD in the
> - * tree and dirty it if necessary.
> - */
> - old = dax_lock_entry(xas, new_entry);
> - WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
> - DAX_LOCKED));
> - entry = new_entry;
> - } else {
> - xas_load(xas); /* Walk the xa_state */
> - }
> -
> - if (dirty)
> - xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
> -
> - if (cow)
> - xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
> -
> - xas_unlock_irq(xas);
> - *pentry = entry;
> - return 0;
> -}
> -
> -static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
> - struct address_space *mapping, void *entry)
> -{
> - unsigned long pfn, index, count, end;
> - long ret = 0;
> - struct vm_area_struct *vma;
> -
> - /*
> - * A page got tagged dirty in DAX mapping? Something is seriously
> - * wrong.
> - */
> - if (WARN_ON(!xa_is_value(entry)))
> - return -EIO;
> -
> - if (unlikely(dax_is_locked(entry))) {
> - void *old_entry = entry;
> -
> - entry = get_unlocked_entry(xas, 0);
> -
> - /* Entry got punched out / reallocated? */
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> - goto put_unlocked;
> - /*
> - * Entry got reallocated elsewhere? No need to writeback.
> - * We have to compare pfns as we must not bail out due to
> - * difference in lockbit or entry type.
> - */
> - if (dax_to_pfn(old_entry) != dax_to_pfn(entry))
> - goto put_unlocked;
> - if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
> - dax_is_zero_entry(entry))) {
> - ret = -EIO;
> - goto put_unlocked;
> - }
> -
> - /* Another fsync thread may have already done this entry */
> - if (!xas_get_mark(xas, PAGECACHE_TAG_TOWRITE))
> - goto put_unlocked;
> - }
> -
> - /* Lock the entry to serialize with page faults */
> - dax_lock_entry(xas, entry);
> -
> - /*
> - * We can clear the tag now but we have to be careful so that concurrent
> - * dax_writeback_one() calls for the same index cannot finish before we
> - * actually flush the caches. This is achieved as the calls will look
> - * at the entry only under the i_pages lock and once they do that
> - * they will see the entry locked and wait for it to unlock.
> - */
> - xas_clear_mark(xas, PAGECACHE_TAG_TOWRITE);
> - xas_unlock_irq(xas);
> -
> - /*
> - * If dax_writeback_mapping_range() was given a wbc->range_start
> - * in the middle of a PMD, the 'index' we use needs to be
> - * aligned to the start of the PMD.
> - * This allows us to flush for PMD_SIZE and not have to worry about
> - * partial PMD writebacks.
> - */
> - pfn = dax_to_pfn(entry);
> - count = 1UL << dax_entry_order(entry);
> - index = xas->xa_index & ~(count - 1);
> - end = index + count - 1;
> -
> - /* Walk all mappings of a given index of a file and writeprotect them */
> - i_mmap_lock_read(mapping);
> - vma_interval_tree_foreach(vma, &mapping->i_mmap, index, end) {
> - pfn_mkclean_range(pfn, count, index, vma);
> - cond_resched();
> - }
> - i_mmap_unlock_read(mapping);
> -
> - dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
> - /*
> - * After we have flushed the cache, we can clear the dirty tag. There
> - * cannot be new dirty data in the pfn after the flush has completed as
> - * the pfn mappings are writeprotected and fault waits for mapping
> - * entry lock.
> - */
> - xas_reset(xas);
> - xas_lock_irq(xas);
> - xas_store(xas, entry);
> - xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
> - dax_wake_entry(xas, entry, WAKE_NEXT);
> -
> - trace_dax_writeback_one(mapping->host, index, count);
> - return ret;
> -
> - put_unlocked:
> - put_unlocked_entry(xas, entry, WAKE_NEXT);
> - return ret;
> -}
> -
> /*
> * Flush the mapping to the persistent domain within the byte range of [start,
> * end]. This is required by data integrity operations to ensure file data is
> @@ -1219,6 +191,37 @@ static int dax_iomap_cow_copy(loff_t pos, uint64_t length, size_t align_size,
> return 0;
> }
>
> +/*
> + * MAP_SYNC on a dax mapping guarantees dirty metadata is
> + * flushed on write-faults (non-cow), but not read-faults.
> + */
> +static bool dax_fault_is_synchronous(const struct iomap_iter *iter,
> + struct vm_area_struct *vma)
> +{
> + return (iter->flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC) &&
> + (iter->iomap.flags & IOMAP_F_DIRTY);
> +}
> +
> +static bool dax_fault_is_cow(const struct iomap_iter *iter)
> +{
> + return (iter->flags & IOMAP_WRITE) &&
> + (iter->iomap.flags & IOMAP_F_SHARED);
> +}
> +
> +static unsigned long dax_iter_flags(const struct iomap_iter *iter,
> + struct vm_fault *vmf)
> +{
> + unsigned long flags = 0;
> +
> + if (!dax_fault_is_synchronous(iter, vmf->vma))
> + flags |= DAX_DIRTY;
> +
> + if (dax_fault_is_cow(iter))
> + flags |= DAX_COW;
> +
> + return flags;
> +}
> +
> /*
> * The user has performed a load from a hole in the file. Allocating a new
> * page in the file would cause excessive storage usage for workloads with
> @@ -1701,7 +704,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
> if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
> iter.flags |= IOMAP_WRITE;
>
> - entry = grab_mapping_entry(&xas, mapping, 0);
> + entry = dax_grab_mapping_entry(&xas, mapping, 0);
> if (xa_is_internal(entry)) {
> ret = xa_to_internal(entry);
> goto out;
> @@ -1818,12 +821,12 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
> goto fallback;
>
> /*
> - * grab_mapping_entry() will make sure we get an empty PMD entry,
> + * dax_grab_mapping_entry() will make sure we get an empty PMD entry,
> * a zero PMD entry or a DAX PMD. If it can't (because a PTE
> * entry is already in the array, for instance), it will return
> * VM_FAULT_FALLBACK.
> */
> - entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
> + entry = dax_grab_mapping_entry(&xas, mapping, PMD_ORDER);
> if (xa_is_internal(entry)) {
> ret = xa_to_internal(entry);
> goto fallback;
> @@ -1897,50 +900,6 @@ vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
> }
> EXPORT_SYMBOL_GPL(dax_iomap_fault);
>
> -/*
> - * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
> - * @vmf: The description of the fault
> - * @pfn: PFN to insert
> - * @order: Order of entry to insert.
> - *
> - * This function inserts a writeable PTE or PMD entry into the page tables
> - * for an mmaped DAX file. It also marks the page cache entry as dirty.
> - */
> -static vm_fault_t
> -dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order)
> -{
> - struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> - XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, order);
> - void *entry;
> - vm_fault_t ret;
> -
> - xas_lock_irq(&xas);
> - entry = get_unlocked_entry(&xas, order);
> - /* Did we race with someone splitting entry or so? */
> - if (!entry || dax_is_conflict(entry) ||
> - (order == 0 && !dax_is_pte_entry(entry))) {
> - put_unlocked_entry(&xas, entry, WAKE_NEXT);
> - xas_unlock_irq(&xas);
> - trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
> - VM_FAULT_NOPAGE);
> - return VM_FAULT_NOPAGE;
> - }
> - xas_set_mark(&xas, PAGECACHE_TAG_DIRTY);
> - dax_lock_entry(&xas, entry);
> - xas_unlock_irq(&xas);
> - if (order == 0)
> - ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
> -#ifdef CONFIG_FS_DAX_PMD
> - else if (order == PMD_ORDER)
> - ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE);
> -#endif
> - else
> - ret = VM_FAULT_FALLBACK;
> - dax_unlock_entry(&xas, entry);
> - trace_dax_insert_pfn_mkwrite(mapping->host, vmf, ret);
> - return ret;
> -}
> -
> /**
> * dax_finish_sync_fault - finish synchronous page fault
> * @vmf: The description of the fault
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index f6acb4ed73cb..de60a34088bb 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -157,15 +157,33 @@ static inline void fs_put_dax(struct dax_device *dax_dev, void *holder)
> int dax_writeback_mapping_range(struct address_space *mapping,
> struct dax_device *dax_dev, struct writeback_control *wbc);
>
> -struct page *dax_zap_mappings(struct address_space *mapping);
> -struct page *dax_zap_mappings_range(struct address_space *mapping, loff_t start,
> - loff_t end);
> +#else
> +static inline int dax_writeback_mapping_range(struct address_space *mapping,
> + struct dax_device *dax_dev, struct writeback_control *wbc)
> +{
> + return -EOPNOTSUPP;
> +}
> +
> +#endif
> +
> +int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
> + const struct iomap_ops *ops);
> +int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
> + const struct iomap_ops *ops);
> +
> +#if IS_ENABLED(CONFIG_DAX)
> +int dax_read_lock(void);
> +void dax_read_unlock(int id);
> dax_entry_t dax_lock_page(struct page *page);
> void dax_unlock_page(struct page *page, dax_entry_t cookie);
> +void run_dax(struct dax_device *dax_dev);
> dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
> unsigned long index, struct page **page);
> void dax_unlock_mapping_entry(struct address_space *mapping,
> unsigned long index, dax_entry_t cookie);
> +struct page *dax_zap_mappings(struct address_space *mapping);
> +struct page *dax_zap_mappings_range(struct address_space *mapping, loff_t start,
> + loff_t end);
> #else
> static inline struct page *dax_zap_mappings(struct address_space *mapping)
> {
> @@ -179,12 +197,6 @@ static inline struct page *dax_zap_mappings_range(struct address_space *mapping,
> return NULL;
> }
>
> -static inline int dax_writeback_mapping_range(struct address_space *mapping,
> - struct dax_device *dax_dev, struct writeback_control *wbc)
> -{
> - return -EOPNOTSUPP;
> -}
> -
> static inline dax_entry_t dax_lock_page(struct page *page)
> {
> if (IS_DAX(page->mapping->host))
> @@ -196,6 +208,15 @@ static inline void dax_unlock_page(struct page *page, dax_entry_t cookie)
> {
> }
>
> +static inline int dax_read_lock(void)
> +{
> + return 0;
> +}
> +
> +static inline void dax_read_unlock(int id)
> +{
> +}
> +
> static inline dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
> unsigned long index, struct page **page)
> {
> @@ -208,11 +229,6 @@ static inline void dax_unlock_mapping_entry(struct address_space *mapping,
> }
> #endif
>
> -int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
> - const struct iomap_ops *ops);
> -int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
> - const struct iomap_ops *ops);
> -
> /*
> * Document all the code locations that want know when a dax page is
> * unreferenced.
> @@ -222,19 +238,6 @@ static inline bool dax_page_idle(struct page *page)
> return page_ref_count(page) == 1;
> }
>
> -#if IS_ENABLED(CONFIG_DAX)
> -int dax_read_lock(void);
> -void dax_read_unlock(int id);
> -#else
> -static inline int dax_read_lock(void)
> -{
> - return 0;
> -}
> -
> -static inline void dax_read_unlock(int id)
> -{
> -}
> -#endif /* CONFIG_DAX */
> bool dax_alive(struct dax_device *dax_dev);
> void *dax_get_private(struct dax_device *dax_dev);
> long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
> @@ -255,6 +258,9 @@ vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
> pfn_t *pfnp, int *errp, const struct iomap_ops *ops);
> vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
> enum page_entry_size pe_size, pfn_t pfn);
> +void *dax_grab_mapping_entry(struct xa_state *xas,
> + struct address_space *mapping, unsigned int order);
> +void dax_unlock_entry(struct xa_state *xas, void *entry);
> int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
> int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
> pgoff_t index);
> @@ -271,6 +277,56 @@ static inline bool dax_mapping(struct address_space *mapping)
> return mapping->host && IS_DAX(mapping->host);
> }
>
> +/*
> + * DAX pagecache entries use XArray value entries so they can't be mistaken
> + * for pages. We use one bit for locking, one bit for the entry size (PMD)
> + * and two more to tell us if the entry is a zero page or an empty entry that
> + * is just used for locking. In total four special bits.
> + *
> + * If the PMD bit isn't set the entry has size PAGE_SIZE, and if the ZERO_PAGE
> + * and EMPTY bits aren't set the entry is a normal DAX entry with a filesystem
> + * block allocation.
> + */
> +#define DAX_SHIFT (5)
> +#define DAX_MASK ((1UL << DAX_SHIFT) - 1)
> +#define DAX_LOCKED (1UL << 0)
> +#define DAX_PMD (1UL << 1)
> +#define DAX_ZERO_PAGE (1UL << 2)
> +#define DAX_EMPTY (1UL << 3)
> +#define DAX_ZAP (1UL << 4)
> +
> +/*
> + * These flags are not conveyed in Xarray value entries, they are just
> + * modifiers to dax_insert_entry().
> + */
> +#define DAX_DIRTY (1UL << (DAX_SHIFT + 0))
> +#define DAX_COW (1UL << (DAX_SHIFT + 1))
> +
> +vm_fault_t dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
> + void **pentry, pfn_t pfn, unsigned long flags);
> +vm_fault_t dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn,
> + unsigned int order);
> +int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
> + struct address_space *mapping, void *entry);
> +
> +/* The 'colour' (ie low bits) within a PMD of a page offset. */
> +#define PG_PMD_COLOUR ((PMD_SIZE >> PAGE_SHIFT) - 1)
> +#define PG_PMD_NR (PMD_SIZE >> PAGE_SHIFT)
> +
> +/* The order of a PMD entry */
> +#define PMD_ORDER (PMD_SHIFT - PAGE_SHIFT)
> +
> +static inline unsigned int pe_order(enum page_entry_size pe_size)
> +{
> + if (pe_size == PE_SIZE_PTE)
> + return PAGE_SHIFT - PAGE_SHIFT;
> + if (pe_size == PE_SIZE_PMD)
> + return PMD_SHIFT - PAGE_SHIFT;
> + if (pe_size == PE_SIZE_PUD)
> + return PUD_SHIFT - PAGE_SHIFT;
> + return ~0;
> +}
> +
> #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
> void hmem_register_device(int target_nid, struct resource *r);
> #else
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index fd57407e7f3d..e5d30eec3bf1 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -221,6 +221,12 @@ static inline void devm_memunmap_pages(struct device *dev,
> {
> }
>
> +static inline struct dev_pagemap *
> +get_dev_pagemap_many(unsigned long pfn, struct dev_pagemap *pgmap, int refs)
> +{
> + return NULL;
> +}
> +
> static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> struct dev_pagemap *pgmap)
> {
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