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Message-ID: <c379c99f-2466-6056-4dd6-90d0a202c13c@collabora.com>
Date: Tue, 18 Jul 2023 13:18:20 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Andrei Vagin <avagin@...il.com>
Cc: Muhammad Usama Anjum <usama.anjum@...labora.com>,
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 7/17/23 10:26 PM, Andrei Vagin wrote:
> 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>
Thank you.
>
> 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.
Sure. I'll add.
>
>> +
>> +#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
#define PAGE_IS_PFNZERO (1 << 4)
PAGE_IS_PFNZERO macro cannot be used 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.
Sure.
>
>> +};
>> +
>> +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.
We haven't added it as other existing code such as mincore() and
pagemap_read() don't have it either. Also mmap_read_lock_killable would
return error if there is some critical single pending.
>
>> + 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.
No, ret could get replaced by error if copy_to_user() fails. So we have to
do this before that.
>
>> +
>> + 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
>>
--
BR,
Muhammad Usama Anjum
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