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Message-ID: <CANaxB-zMhhi+kHZ+3w9yzogo6fKjR=swBkuA-s88Qs5oeLRAYQ@mail.gmail.com>
Date: Mon, 17 Jul 2023 10:26:41 -0700
From: Andrei Vagin <avagin@...il.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Michał Mirosław <emmir@...gle.com>,
Danylo Mocherniuk <mdanylo@...gle.com>,
Paul Gofman <pgofman@...eweavers.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Yang Shi <shy828301@...il.com>,
Vlastimil Babka <vbabka@...e.cz>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Yun Zhou <yun.zhou@...driver.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Alex Sierra <alex.sierra@....com>,
Matthew Wilcox <willy@...radead.org>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: Re: [PATCH v25 2/5] fs/proc/task_mmu: Implement IOCTL to get and
optionally clear info about PTEs
On Thu, Jul 13, 2023 at 3:14 AM Muhammad Usama Anjum
<usama.anjum@...labora.com> wrote:
>
> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
> the info about page table entries. The following operations are supported
> in this ioctl:
> - Get the information if the pages have been written-to (PAGE_IS_WRITTEN),
> file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT), swapped
> (PAGE_IS_SWAPPED) or page has pfn zero (PAGE_IS_PFNZERO).
> - Find pages which have been written-to and/or write protect the pages
> (atomic PM_SCAN_OP_GET + PM_SCAN_OP_WP)
>
> This IOCTL can be extended to get information about more PTE bits. The
> entire address range passed by user [start, end) is scanned until either
> the user provided buffer is full or max_pages have been found.
>
Reviewed-by: Andrei Vagin <avagin@...il.com>
Here are a few inline comments.
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> ---
> Changes in v25:
> - Do proper filtering on hole as well (hole got missed earlier)
>
> Changes in v24:
> - Place WP markers in case of hole as well
>
> Changes in v23:
> - Set vec_buf_index to 0 only when vec_buf_index is set
> - Return -EFAULT instead of -EINVAL if vec is NULL
> - Correctly return the walk ending address to the page granularity
>
> Changes in v22:
> - Interface change to return walk ending address to user:
> - Replace [start start + len) with [start, end)
> - Return the ending address of the address walk in start
>
> Changes in v21:
> - Abort walk instead of returning error if WP is to be performed on
> partial hugetlb
> - Changed the data types of some variables in pagemap_scan_private to
> long
>
> Changes in v20:
> - Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO
>
> Changes in v19:
> - Interface changes such as renaming, return mask and WP can be used
> with any flags specified in masks
> - Internal code changes
>
> Changes in v18:
> - Rebased on top of next-20230613
> - ptep_get() updates
> - remove pmd_trans_unstable() and add ACTION_AGAIN
> - Review updates (Micheal)
>
> Changes in v17:
> - Rebased on next-20230606
> - Made make_uffd_wp_*_pte() better and minor changes
>
> Changes in v16:
> - Fixed a corner case where kernel writes beyond user buffer by one
> element
> - Bring back exclusive PM_SCAN_OP_WP
> - Cosmetic changes
>
> Changes in v15:
> - Build fix:
> - Use generic tlb flush function in pagemap_scan_pmd_entry() instead of
> using x86 specific flush function in do_pagemap_scan()
> - Remove #ifdef from pagemap_scan_hugetlb_entry()
> - Use mm instead of undefined vma->vm_mm
>
> Changes in v14:
> - Fix build error caused by #ifdef added at last minute in some configs
>
> Changes in v13:
> - Review updates
> - mmap_read_lock_killable() instead of mmap_read_lock()
> - Replace uffd_wp_range() with helpers which increases performance
> drastically for OP_WP operations by reducing the number of tlb
> flushing etc
> - Add MMU_NOTIFY_PROTECTION_VMA notification for the memory range
>
> Changes in v12:
> - Add hugetlb support to cover all memory types
> - Merge "userfaultfd: Define dummy uffd_wp_range()" with this patch
> - Review updates to the code
>
> Changes in v11:
> - Find written pages in a better way
> - Fix a corner case (thanks Paul)
> - Improve the code/comments
> - remove ENGAGE_WP + ! GET operation
> - shorten the commit message in favour of moving documentation to
> pagemap.rst
>
> Changes in v10:
> - move changes in tools/include/uapi/linux/fs.h to separate patch
> - update commit message
>
> Change in v8:
> - Correct is_pte_uffd_wp()
> - Improve readability and error checks
> - Remove some un-needed code
>
> Changes in v7:
> - Rebase on top of latest next
> - Fix some corner cases
> - Base soft-dirty on the uffd wp async
> - Update the terminologies
> - Optimize the memory usage inside the ioctl
> ---
> fs/proc/task_mmu.c | 591 ++++++++++++++++++++++++++++++++++++++++
> include/linux/hugetlb.h | 1 +
> include/uapi/linux/fs.h | 55 ++++
> mm/hugetlb.c | 2 +-
> 4 files changed, 648 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index cfab855fe7e9..596fdfdc4387 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -19,6 +19,7 @@
> #include <linux/shmem_fs.h>
> #include <linux/uaccess.h>
> #include <linux/pkeys.h>
> +#include <linux/minmax.h>
>
> #include <asm/elf.h>
> #include <asm/tlb.h>
> @@ -1768,11 +1769,601 @@ static int pagemap_release(struct inode *inode, struct file *file)
> return 0;
> }
>
> +#define PM_SCAN_REQUIRE_UFFD (1ULL << 63)
> +
> +#define PM_SCAN_FOUND_MAX_PAGES (1)
> +#define PM_SCAN_END_WALK (-256)
I would add a comment to explain why one is negative and another one
is positive.
> +
> +#define PM_SCAN_BITS_ALL (PAGE_IS_WRITTEN | PAGE_IS_FILE | \
> + PAGE_IS_PRESENT | PAGE_IS_SWAPPED | \
> + PAGE_IS_PFNZERO)
> +#define PM_SCAN_OPS (PM_SCAN_OP_GET | PM_SCAN_OP_WP)
> +#define IS_PM_SCAN_GET(flags) (flags & PM_SCAN_OP_GET)
> +#define IS_PM_SCAN_WP(flags) (flags & PM_SCAN_OP_WP)
> +
> +#define PM_SCAN_FLAGS(wt, file, present, swap, pfnzero) \
> + ((wt) | ((file) << 1) | ((present) << 2) | \
> + ((swap) << 3) | ((pfnzero) << 4))
it is better to use PAGE_IS_* constants here
> +
> +struct pagemap_scan_private {
> + struct page_region *vec_buf, cur_buf;
> + unsigned long vec_buf_len, vec_buf_index, max_pages, found_pages;
> + unsigned long long flags, required_mask, anyof_mask, excluded_mask, return_mask, end_addr;
end_addr has to be unsigned long.
> +};
> +
> +static inline bool is_pte_uffd_wp(pte_t pte)
> +{
> + return (pte_present(pte) && pte_uffd_wp(pte)) ||
> + pte_swp_uffd_wp_any(pte);
> +}
> +
> +static inline void make_uffd_wp_pte(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *pte)
> +{
> + pte_t ptent = ptep_get(pte);
> +
> + if (pte_present(ptent)) {
> + pte_t old_pte;
> +
> + old_pte = ptep_modify_prot_start(vma, addr, pte);
> + ptent = pte_mkuffd_wp(ptent);
> + ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent);
> + } else if (is_swap_pte(ptent)) {
> + ptent = pte_swp_mkuffd_wp(ptent);
> + set_pte_at(vma->vm_mm, addr, pte, ptent);
> + } else {
> + set_pte_at(vma->vm_mm, addr, pte,
> + make_pte_marker(PTE_MARKER_UFFD_WP));
> + }
> +}
> +
> +static inline bool pagemap_scan_is_file(struct vm_area_struct *vma, pte_t ptent,
> + unsigned long addr)
> +{
> + struct page *page = NULL;
> + swp_entry_t entry;
> +
> + if (pte_present(ptent)) {
> + page = vm_normal_page(vma, addr, ptent);
> + } else {
> + entry = pte_to_swp_entry(ptent);
> + if (is_pfn_swap_entry(entry))
> + page = pfn_swap_entry_to_page(entry);
> + }
> +
> + if (page && !PageAnon(page))
> + return true;
> +
> + return false;
> +}
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline bool is_pmd_uffd_wp(pmd_t pmd)
> +{
> + return (pmd_present(pmd) && pmd_uffd_wp(pmd)) ||
> + (is_swap_pmd(pmd) && pmd_swp_uffd_wp(pmd));
> +}
> +
> +static inline void make_uffd_wp_pmd(struct vm_area_struct *vma,
> + unsigned long addr, pmd_t *pmdp)
> +{
> + pmd_t old, pmd = *pmdp;
> +
> + if (pmd_present(pmd)) {
> + old = pmdp_invalidate_ad(vma, addr, pmdp);
> + pmd = pmd_mkuffd_wp(old);
> + set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
> + } else if (is_migration_entry(pmd_to_swp_entry(pmd))) {
> + pmd = pmd_swp_mkuffd_wp(pmd);
> + set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
> + }
> +}
> +#endif
> +
> +#ifdef CONFIG_HUGETLB_PAGE
> +static inline bool is_huge_pte_uffd_wp(pte_t pte)
> +{
> + return (pte_present(pte) && huge_pte_uffd_wp(pte)) ||
> + pte_swp_uffd_wp_any(pte);
> +}
> +
> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep,
> + pte_t ptent)
> +{
> + if (is_hugetlb_entry_hwpoisoned(ptent) || is_pte_marker(ptent))
> + return;
> +
> + if (is_hugetlb_entry_migration(ptent))
> + set_huge_pte_at(vma->vm_mm, addr, ptep,
> + pte_swp_mkuffd_wp(ptent));
> + else if (!huge_pte_none(ptent))
> + huge_ptep_modify_prot_commit(vma, addr, ptep, ptent,
> + huge_pte_mkuffd_wp(ptent));
> + else
> + set_huge_pte_at(vma->vm_mm, addr, ptep,
> + make_pte_marker(PTE_MARKER_UFFD_WP));
> +}
> +
> +static inline bool pagemap_scan_is_huge_file(pte_t pte)
> +{
> + if (pte_present(pte) && (!PageAnon(pte_page(pte))))
> + return true;
> +
> + return false;
> +}
> +#endif
> +
> +static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
> + struct mm_walk *walk)
> +{
> + struct pagemap_scan_private *p = walk->private;
> + struct vm_area_struct *vma = walk->vma;
> +
> + if ((p->flags & PM_SCAN_REQUIRE_UFFD) && (!userfaultfd_wp_async(vma) ||
> + !userfaultfd_wp_use_markers(vma)))
> + return -EPERM;
> +
> + if (vma->vm_flags & VM_PFNMAP)
> + return 1;
> +
> + return 0;
> +}
> +
> +static int pagemap_scan_output(unsigned long bitmap,
> + struct pagemap_scan_private *p,
> + unsigned long addr, unsigned int n_pages)
> +{
> + struct page_region *cur_buf = &p->cur_buf;
> +
> + bitmap &= p->return_mask;
> +
> + if (cur_buf->flags == bitmap &&
> + cur_buf->start + cur_buf->len * PAGE_SIZE == addr) {
> + cur_buf->len += n_pages;
> + p->found_pages += n_pages;
> + } else {
> + if (cur_buf->len) {
> + if (p->vec_buf_index >= p->vec_buf_len) {
> + p->end_addr = addr;
> + return PM_SCAN_END_WALK;
> + }
> +
> + memcpy(&p->vec_buf[p->vec_buf_index], cur_buf,
> + sizeof(*p->vec_buf));
> + p->vec_buf_index++;
> + }
> +
> + cur_buf->start = addr;
> + cur_buf->len = n_pages;
> + cur_buf->flags = bitmap;
> + p->found_pages += n_pages;
> + }
> +
> + if (p->found_pages == p->max_pages) {
> + p->end_addr = addr + n_pages * PAGE_SIZE;
> + return PM_SCAN_FOUND_MAX_PAGES;
> + }
> +
> + return 0;
> +}
> +
> +static bool pagemap_scan_is_interesting_page(unsigned long bitmap,
> + struct pagemap_scan_private *p)
> +{
> + if ((p->required_mask & bitmap) != p->required_mask)
> + return false;
> + if (p->anyof_mask && !(p->anyof_mask & bitmap))
> + return false;
> + if (p->excluded_mask & bitmap)
> + return false;
> +
> + return true;
> +}
> +
> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> + unsigned long end, struct mm_walk *walk)
> +{
> + bool is_written, flush = false, interesting = true;
> + struct pagemap_scan_private *p = walk->private;
> + struct vm_area_struct *vma = walk->vma;
> + unsigned long bitmap, addr = end;
> + pte_t *pte, *orig_pte, ptent;
> + spinlock_t *ptl;
> + int ret = 0;
> +
> + arch_enter_lazy_mmu_mode();
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + ptl = pmd_trans_huge_lock(pmd, vma);
> + if (ptl) {
> + unsigned long n_pages = (end - start)/PAGE_SIZE;
> +
> + if (n_pages > p->max_pages - p->found_pages)
> + n_pages = p->max_pages - p->found_pages;
> +
> + is_written = !is_pmd_uffd_wp(*pmd);
> +
> + bitmap = PM_SCAN_FLAGS(is_written, false,
> + pmd_present(*pmd), is_swap_pmd(*pmd),
> + pmd_present(*pmd) && is_zero_pfn(pmd_pfn(*pmd)));
> +
> + if (IS_PM_SCAN_GET(p->flags))
> + interesting = pagemap_scan_is_interesting_page(bitmap, p);
> +
> + if (interesting) {
> + /*
> + * Break huge page into small pages if the WP operation
> + * need to be performed is on a portion of the huge page.
> + */
> + if (is_written && IS_PM_SCAN_WP(p->flags) &&
> + n_pages < HPAGE_SIZE/PAGE_SIZE) {
> + spin_unlock(ptl);
> +
> + split_huge_pmd(vma, pmd, start);
> + goto process_smaller_pages;
> + }
> +
> + if (IS_PM_SCAN_GET(p->flags))
> + ret = pagemap_scan_output(bitmap, p, start, n_pages);
> +
> + if (IS_PM_SCAN_WP(p->flags) && is_written && ret >= 0) {
> + make_uffd_wp_pmd(vma, start, pmd);
> + flush_tlb_range(vma, start, end);
> + }
> + }
> +
> + spin_unlock(ptl);
> + arch_leave_lazy_mmu_mode();
> +
> + return ret;
> + }
> +
> +process_smaller_pages:
> +#endif
> +
> + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
> + if (!pte) {
> + walk->action = ACTION_AGAIN;
> + return 0;
> + }
> +
> + for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
> + ptent = ptep_get(pte);
> + is_written = !is_pte_uffd_wp(ptent);
> +
> + bitmap = PM_SCAN_FLAGS(is_written, pagemap_scan_is_file(vma, ptent, addr),
> + pte_present(ptent), is_swap_pte(ptent),
> + pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
> +
> + if (IS_PM_SCAN_GET(p->flags)) {
> + interesting = pagemap_scan_is_interesting_page(bitmap, p);
> + if (interesting)
> + ret = pagemap_scan_output(bitmap, p, addr, 1);
> + }
> +
> + if (IS_PM_SCAN_WP(p->flags) && is_written && interesting &&
> + ret >= 0) {
> + make_uffd_wp_pte(vma, addr, pte);
> + flush = true;
> + }
> + }
> +
> + if (flush)
> + flush_tlb_range(vma, start, addr);
> +
> + pte_unmap_unlock(orig_pte, ptl);
> + arch_leave_lazy_mmu_mode();
> +
> + cond_resched();
> + return ret;
> +}
> +
> +#ifdef CONFIG_HUGETLB_PAGE
> +static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask,
> + unsigned long start, unsigned long end,
> + struct mm_walk *walk)
> +{
> + unsigned long n_pages = (end - start)/PAGE_SIZE;
> + struct pagemap_scan_private *p = walk->private;
> + struct vm_area_struct *vma = walk->vma;
> + bool is_written, interesting = true;
> + struct hstate *h = hstate_vma(vma);
> + unsigned long bitmap;
> + spinlock_t *ptl;
> + int ret = 0;
> + pte_t ptent;
> +
> + if (IS_PM_SCAN_WP(p->flags) && n_pages < HPAGE_SIZE/PAGE_SIZE) {
> + p->end_addr = start;
> + return -EINVAL;
> + }
> +
> + if (n_pages > p->max_pages - p->found_pages)
> + n_pages = p->max_pages - p->found_pages;
> +
> + if (IS_PM_SCAN_WP(p->flags)) {
> + i_mmap_lock_write(vma->vm_file->f_mapping);
> + ptl = huge_pte_lock(h, vma->vm_mm, ptep);
> + }
> +
> + ptent = huge_ptep_get(ptep);
> + is_written = !is_huge_pte_uffd_wp(ptent);
> +
> + bitmap = PM_SCAN_FLAGS(is_written, pagemap_scan_is_huge_file(ptent),
> + pte_present(ptent), is_swap_pte(ptent),
> + pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
> +
> + if (IS_PM_SCAN_GET(p->flags))
> + interesting = pagemap_scan_is_interesting_page(bitmap, p);
> +
> + if (interesting) {
> + /*
> + * Partial hugetlb page clear isn't supported
> + */
> + if (is_written && IS_PM_SCAN_WP(p->flags) &&
> + n_pages < HPAGE_SIZE/PAGE_SIZE) {
> + ret = PM_SCAN_END_WALK;
> + p->end_addr = start;
> + goto unlock_and_return;
> + }
> +
> + if (IS_PM_SCAN_GET(p->flags))
> + ret = pagemap_scan_output(bitmap, p, start, n_pages);
> +
> + if (IS_PM_SCAN_WP(p->flags) && is_written && ret >= 0) {
> + make_uffd_wp_huge_pte(vma, start, ptep, ptent);
> + flush_hugetlb_tlb_range(vma, start, end);
> + }
> + }
> +
> +unlock_and_return:
> + if (IS_PM_SCAN_WP(p->flags)) {
> + spin_unlock(ptl);
> + i_mmap_unlock_write(vma->vm_file->f_mapping);
> + }
> +
> + return ret;
> +}
> +#else
> +#define pagemap_scan_hugetlb_entry NULL
> +#endif
> +
> +static int pagemap_scan_pte_hole(unsigned long addr, unsigned long end,
> + int depth, struct mm_walk *walk)
> +{
> + unsigned long n_pages = (end - addr)/PAGE_SIZE;
> + struct pagemap_scan_private *p = walk->private;
> + struct vm_area_struct *vma = walk->vma;
> + bool interesting = true;
> + unsigned long bitmap;
> + int ret = 0;
> +
> + if (!vma)
> + return 0;
> +
> + bitmap = PM_SCAN_FLAGS(false, false, false, false, false);
> +
> + if (IS_PM_SCAN_GET(p->flags))
> + interesting = pagemap_scan_is_interesting_page(bitmap, p);
> +
> + if (interesting) {
> + if (IS_PM_SCAN_GET(p->flags)) {
> + if (n_pages > p->max_pages - p->found_pages)
> + n_pages = p->max_pages - p->found_pages;
> +
> + ret = pagemap_scan_output(bitmap, p, addr, n_pages);
> + }
> +
> + if (IS_PM_SCAN_WP(p->flags) && !ret &&
> + uffd_wp_range(vma, addr, end - addr, true) < 0)
Why do we need to call uffd_wp_range for holes? Should we call
flush_tlb_range after it?
> + ret = -EINVAL;
> + }
> +
> + return ret;
> +}
> +
> +static const struct mm_walk_ops pagemap_scan_ops = {
> + .test_walk = pagemap_scan_test_walk,
> + .pmd_entry = pagemap_scan_pmd_entry,
> + .pte_hole = pagemap_scan_pte_hole,
> + .hugetlb_entry = pagemap_scan_hugetlb_entry,
> +};
> +
> +static int pagemap_scan_args_valid(struct pm_scan_arg *arg, unsigned long start,
> + unsigned long end, struct page_region __user *vec)
> +{
> + /* Detect illegal size, flags, len and masks */
> + if (arg->size != sizeof(struct pm_scan_arg))
> + return -EINVAL;
> + if (!arg->flags)
> + return -EINVAL;
> + if (arg->flags & ~PM_SCAN_OPS)
> + return -EINVAL;
> + if (!(end - start))
> + return -EINVAL;
> + if ((arg->required_mask | arg->anyof_mask | arg->excluded_mask |
> + arg->return_mask) & ~PM_SCAN_BITS_ALL)
> + return -EINVAL;
> + if (!arg->required_mask && !arg->anyof_mask &&
> + !arg->excluded_mask)
> + return -EINVAL;
> + if (!arg->return_mask)
> + return -EINVAL;
> +
> + /* Validate memory range */
> + if (!IS_ALIGNED(start, PAGE_SIZE))
> + return -EINVAL;
> + if (!access_ok((void __user *)start, end - start))
> + return -EFAULT;
> +
> + if (IS_PM_SCAN_GET(arg->flags)) {
> + if (arg->vec_len == 0)
> + return -EINVAL;
> + if (!vec)
> + return -EFAULT;
> + if (!access_ok((void __user *)vec,
> + arg->vec_len * sizeof(struct page_region)))
> + return -EFAULT;
> + }
> +
> + if (IS_PM_SCAN_WP(arg->flags) && !IS_PM_SCAN_GET(arg->flags) &&
> + arg->max_pages)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long __arg)
> +{
> + struct pm_scan_arg __user *uarg = (struct pm_scan_arg __user *)__arg;
> + unsigned long long start, end, walk_start, walk_end;
> + unsigned long empty_slots, vec_index = 0;
> + struct mmu_notifier_range range;
> + struct page_region __user *vec;
> + struct pagemap_scan_private p;
> + struct pm_scan_arg arg;
> + int ret = 0;
> +
> + if (copy_from_user(&arg, uarg, sizeof(arg)))
> + return -EFAULT;
> +
> + start = untagged_addr((unsigned long)arg.start);
> + end = untagged_addr((unsigned long)arg.end);
> + vec = (struct page_region __user *)untagged_addr((unsigned long)arg.vec);
> +
> + ret = pagemap_scan_args_valid(&arg, start, end, vec);
> + if (ret)
> + return ret;
> +
> + p.max_pages = (arg.max_pages) ? arg.max_pages : ULONG_MAX;
> + p.found_pages = 0;
> + p.required_mask = arg.required_mask;
> + p.anyof_mask = arg.anyof_mask;
> + p.excluded_mask = arg.excluded_mask;
> + p.return_mask = arg.return_mask;
> + p.flags = arg.flags;
> + p.flags |= ((p.required_mask | p.anyof_mask | p.excluded_mask) &
> + PAGE_IS_WRITTEN) ? PM_SCAN_REQUIRE_UFFD : 0;
> + p.cur_buf.start = p.cur_buf.len = p.cur_buf.flags = 0;
> + p.vec_buf = NULL;
> + p.vec_buf_len = PAGEMAP_WALK_SIZE >> PAGE_SHIFT;
> + p.vec_buf_index = 0;
> + p.end_addr = 0;
> +
> + /*
> + * Allocate smaller buffer to get output from inside the page walk
> + * functions and walk page range in PAGEMAP_WALK_SIZE size chunks. As
> + * we want to return output to user in compact form where no two
> + * consecutive regions should be continuous and have the same flags.
> + * So store the latest element in p.cur_buf between different walks and
> + * store the p.cur_buf at the end of the walk to the user buffer.
> + */
> + if (IS_PM_SCAN_GET(p.flags)) {
> + p.vec_buf = kmalloc_array(p.vec_buf_len, sizeof(*p.vec_buf),
> + GFP_KERNEL);
> + if (!p.vec_buf)
> + return -ENOMEM;
> + }
> +
> + /*
> + * Protection change for the range is going to happen.
> + */
> + if (IS_PM_SCAN_WP(p.flags)) {
> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
> + mm, start, end);
> + mmu_notifier_invalidate_range_start(&range);
> + }
> +
> + walk_start = walk_end = start;
> + while (walk_end < end && !ret) {
> + if (IS_PM_SCAN_GET(p.flags)) {
> + /*
> + * All data is copied to cur_buf first. When more data
> + * is found, we push cur_buf to vec_buf and copy new
> + * data to cur_buf. Subtract 1 from length as the
> + * index of cur_buf isn't counted in length.
> + */
> + empty_slots = arg.vec_len - vec_index;
> + p.vec_buf_len = min(p.vec_buf_len, empty_slots - 1);
> + }
> +
I still don't understand why we don't want/need to check for pending signals.
> + ret = mmap_read_lock_killable(mm);
> + if (ret)
> + goto out;
> +
> + walk_end = min((walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, end);
> +
> + ret = walk_page_range(mm, walk_start, walk_end,
> + &pagemap_scan_ops, &p);
> + mmap_read_unlock(mm);
> +
> + if (ret == PM_SCAN_FOUND_MAX_PAGES || ret == PM_SCAN_END_WALK)
> + arg.start = p.end_addr;
nit: this check can be moved out of the loop.
> +
> + if (ret && ret != PM_SCAN_FOUND_MAX_PAGES &&
> + ret != PM_SCAN_END_WALK)
> + goto out;
> +
> + if (p.vec_buf_index) {
> + if (copy_to_user(&vec[vec_index], p.vec_buf,
> + p.vec_buf_index * sizeof(*p.vec_buf))) {
> + /*
> + * Return error even though the OP succeeded
> + */
> + ret = -EFAULT;
> + goto out;
> + }
> + vec_index += p.vec_buf_index;
> + p.vec_buf_index = 0;
> + }
> + walk_start = walk_end;
> + }
> +
> + if (p.cur_buf.len) {
> + if (copy_to_user(&vec[vec_index], &p.cur_buf, sizeof(p.cur_buf))) {
> + ret = -EFAULT;
> + goto out;
> + }
> + vec_index++;
> + }
> +
> + ret = vec_index;
> +
> +out:
> + if (!p.end_addr)
> + arg.start = walk_start;
> + if (copy_to_user(&uarg->start, &arg.start, sizeof(arg.start)))
> + ret = -EFAULT;
> +
> + if (IS_PM_SCAN_WP(p.flags))
> + mmu_notifier_invalidate_range_end(&range);
> +
> + kfree(p.vec_buf);
> + return ret;
> +}
> +
> +static long do_pagemap_cmd(struct file *file, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct mm_struct *mm = file->private_data;
> +
> + switch (cmd) {
> + case PAGEMAP_SCAN:
> + return do_pagemap_scan(mm, arg);
> +
> + default:
> + return -EINVAL;
> + }
> +}
> +
> const struct file_operations proc_pagemap_operations = {
> .llseek = mem_lseek, /* borrow this */
> .read = pagemap_read,
> .open = pagemap_open,
> .release = pagemap_release,
> + .unlocked_ioctl = do_pagemap_cmd,
> + .compat_ioctl = do_pagemap_cmd,
> };
> #endif /* CONFIG_PROC_PAGE_MONITOR */
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 623e98d62df3..c44e7bde0339 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma,
> unsigned long cp_flags);
>
> bool is_hugetlb_entry_migration(pte_t pte);
> +bool is_hugetlb_entry_hwpoisoned(pte_t pte);
> void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
>
> #else /* !CONFIG_HUGETLB_PAGE */
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index b7b56871029c..ac684d99e68f 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -305,4 +305,59 @@ typedef int __bitwise __kernel_rwf_t;
> #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> RWF_APPEND)
>
> +/* Pagemap ioctl */
> +#define PAGEMAP_SCAN _IOWR('f', 16, struct pm_scan_arg)
> +
> +/* Bits are set in flags of the page_region and masks in pm_scan_args */
> +#define PAGE_IS_WRITTEN (1 << 0)
> +#define PAGE_IS_FILE (1 << 1)
> +#define PAGE_IS_PRESENT (1 << 2)
> +#define PAGE_IS_SWAPPED (1 << 3)
> +#define PAGE_IS_PFNZERO (1 << 4)
> +
> +/*
> + * struct page_region - Page region with flags
> + * @start: Start of the region
> + * @len: Length of the region in pages
> + * @bitmap: Bits sets for the region
> + */
> +struct page_region {
> + __u64 start;
> + __u64 len;
> + __u64 flags;
> +};
> +
> +/*
> + * struct pm_scan_arg - Pagemap ioctl argument
> + * @size: Size of the structure
> + * @flags: Flags for the IOCTL
> + * @start: Starting address of the region
> + * (Ending address of the walk is also returned in it)
> + * @end: Ending address of the region
> + * @vec: Address of page_region struct array for output
> + * @vec_len: Length of the page_region struct array
> + * @max_pages: Optional max return pages
> + * @required_mask: Required mask - All of these bits have to be set in the PTE
> + * @anyof_mask: Any mask - Any of these bits are set in the PTE
> + * @excluded_mask: Exclude mask - None of these bits are set in the PTE
> + * @return_mask: Bits that are to be reported in page_region
> + */
> +struct pm_scan_arg {
> + __u64 size;
> + __u64 flags;
> + __u64 start;
> + __u64 end;
> + __u64 vec;
> + __u64 vec_len;
> + __u64 max_pages;
> + __u64 required_mask;
> + __u64 anyof_mask;
> + __u64 excluded_mask;
> + __u64 return_mask;
> +};
> +
> +/* Supported flags */
> +#define PM_SCAN_OP_GET (1 << 0)
> +#define PM_SCAN_OP_WP (1 << 1)
> +
> #endif /* _UAPI_LINUX_FS_H */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ee88a2a6649f..f7cefdcb114c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4981,7 +4981,7 @@ bool is_hugetlb_entry_migration(pte_t pte)
> return false;
> }
>
> -static bool is_hugetlb_entry_hwpoisoned(pte_t pte)
> +bool is_hugetlb_entry_hwpoisoned(pte_t pte)
> {
> swp_entry_t swp;
>
> --
> 2.39.2
>
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