The PAGEMAP_SCAN IOCTL on the pagemap file can be used to get or optionally
clear the info about page table entries. The following operations are supported
in this IOCTL:
- Scan the address range and get the memory ranges matching the provided criteria.
This is performed by default when the output buffer is specified.
- Write-protect the pages. The PM_SCAN_WP_MATCHING is used to write-protect
the pages of interest. The PM_SCAN_CHECK_WPASYNC aborts the operation if
non-Async Write Protected pages are found. The ``PM_SCAN_WP_MATCHING`` can be
used with or without PM_SCAN_CHECK_WPASYNC.
- Both of those operations can be combined into one atomic operation where we can
get and write protect the pages as well.
Following flags about pages are currently supported:
- PAGE_IS_WPALLOWED - Page has async-write-protection enabled
- PAGE_IS_WRITTEN - Page has been written to from the time it was write protected
- PAGE_IS_FILE - Page is file backed
- PAGE_IS_PRESENT - Page is present in the memory
- PAGE_IS_SWAPPED - Page is in swapped
- PAGE_IS_PFNZERO - Page has zero PFN
- PAGE_IS_HUGE - Page is THP or Hugetlb backed
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 <[email protected]>
Reviewed-by: Michał Mirosław <[email protected]>
Signed-off-by: Michał Mirosław <[email protected]>
Signed-off-by: Muhammad Usama Anjum <[email protected]>
---
Changes in v29:
- Cosmetic changes
- Add and improve comments
- Remove cur_buf as merging members issue has been removed
Changes in v28:
- Fix walk_end one last time after doing through testing
Changes in v27:
- Add PAGE_IS_HUGE
- Iterate until temporary buffer is full to do less iterations
- Don't check if PAGE_IS_FILE if no mask needs it as it is very
expensive to check per pte
- bring is_interesting_page() outside pagemap_scan_output() to remove
the horrible return value check
- Replace memcpy() with direct copy
- rename end_addr to walk_end_addr in pagemap_scan_private
- Abort walk if fatal_signal_pending()
Changes in v26:
Changes made by Usama:
- Fix the wrong breaking of loop if page isn't interesting, skip intsead
- Untag the address and save them into struct
- Round off the end address to next page
- Correct the partial hugetlb page handling and returning the error
- Rename PAGE_IS_WPASYNC to PAGE_IS_WPALLOWED
- Return walk ending address in walk_end instead of returning in start
as there is potential of replacing the memory tag
Changes by Michał:
1. the API:
a. return ranges as {begin, end} instead of {begin + len};
b. rename match "flags" to 'page categories' everywhere - this makes
it easier to differentiate the ioctl()s categorisation of pages
from struct page flags;
c. change {required + excluded} to {inverted + required}. This was
rejected before, but I'd like to illustrate the difference.
Old interface can be translated to the new by:
categories_inverted = excluded_mask
categories_mask = required_mask | excluded_mask
categories_anyof_mask = anyof_mask
The new way allows filtering by: A & (B | !C)
categories_inverted = C
categories_mask = A
categories_anyof_mask = B | C
e. allow no-op calls
2. the implementation:
a. gather the page-categorising and write-protecting code in one place;
b. optimization: add whole-vma skipping for WP usecase;
c. extracted output limiting code to pagemap_scan_output();
d. extracted range coalescing to pagemap_scan_push_range();
e. extracted THP entry handling to pagemap_scan_thp_entry();
f. added a shortcut for non-WP hugetlb scan; avoids conditional
locking;
g. extracted scan buffer handling code out of do_pagemap_scan();
h. rework output code to always try to write pending ranges; if EFAULT
is generated it always overwrites the original error code;
(the case of SIGKILL is needlessly trying to write the output
now, but this should be rare case and ignoring it makes the code
not needing a goto)
3.Change no-GET operation condition from `arg.return_mask == 0` to
`arg.vec == NULL`. This will allow issuing the ioctl with
return_mask == 0 to gather matching ranges when the exact category
is not interesting. (Anticipated for CRIU scanning a large sparse
anonymous mapping).
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 | 673 ++++++++++++++++++++++++++++++++++++++++
include/linux/hugetlb.h | 1 +
include/uapi/linux/fs.h | 59 ++++
mm/hugetlb.c | 2 +-
4 files changed, 734 insertions(+), 1 deletion(-)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c1e6531cb02ae..5271c634d2dc8 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -19,6 +19,8 @@
#include <linux/shmem_fs.h>
#include <linux/uaccess.h>
#include <linux/pkeys.h>
+#include <linux/minmax.h>
+#include <linux/overflow.h>
#include <asm/elf.h>
#include <asm/tlb.h>
@@ -1749,11 +1751,682 @@ static int pagemap_release(struct inode *inode, struct file *file)
return 0;
}
+#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
+ PAGE_IS_FILE | PAGE_IS_PRESENT | \
+ PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
+ PAGE_IS_HUGE)
+#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
+
+struct pagemap_scan_private {
+ struct pm_scan_arg arg;
+ unsigned long masks_of_interest, cur_vma_category;
+ struct page_region *vec_buf;
+ unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
+ struct page_region __user *vec_out;
+};
+
+static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
+ struct vm_area_struct *vma,
+ unsigned long addr, pte_t pte)
+{
+ unsigned long categories = 0;
+
+ if (pte_present(pte)) {
+ struct page *page;
+
+ categories |= PAGE_IS_PRESENT;
+ if (!pte_uffd_wp(pte))
+ categories |= PAGE_IS_WRITTEN;
+
+ if (p->masks_of_interest & PAGE_IS_FILE) {
+ page = vm_normal_page(vma, addr, pte);
+ if (page && !PageAnon(page))
+ categories |= PAGE_IS_FILE;
+ }
+
+ if (is_zero_pfn(pte_pfn(pte)))
+ categories |= PAGE_IS_PFNZERO;
+ } else if (is_swap_pte(pte)) {
+ swp_entry_t swp;
+
+ categories |= PAGE_IS_SWAPPED;
+ if (!pte_swp_uffd_wp_any(pte))
+ categories |= PAGE_IS_WRITTEN;
+
+ if (p->masks_of_interest & PAGE_IS_FILE) {
+ swp = pte_to_swp_entry(pte);
+ if (is_pfn_swap_entry(swp) &&
+ !PageAnon(pfn_swap_entry_to_page(swp)))
+ categories |= PAGE_IS_FILE;
+ }
+ }
+
+ return categories;
+}
+
+static 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));
+ }
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static unsigned long pagemap_thp_category(pmd_t pmd)
+{
+ unsigned long categories = PAGE_IS_HUGE;
+
+ /*
+ * THPs don't support file-backed memory. So PAGE_IS_FILE
+ * hasn't been checked here.
+ */
+ if (pmd_present(pmd)) {
+ categories |= PAGE_IS_PRESENT;
+ if (!pmd_uffd_wp(pmd))
+ categories |= PAGE_IS_WRITTEN;
+ if (is_zero_pfn(pmd_pfn(pmd)))
+ categories |= PAGE_IS_PFNZERO;
+ } else if (is_swap_pmd(pmd)) {
+ categories |= PAGE_IS_SWAPPED;
+ if (!pmd_swp_uffd_wp(pmd))
+ categories |= PAGE_IS_WRITTEN;
+ }
+
+ return categories;
+}
+
+static 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 /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#ifdef CONFIG_HUGETLB_PAGE
+static unsigned long pagemap_hugetlb_category(pte_t pte)
+{
+ unsigned long categories = PAGE_IS_HUGE;
+
+ /*
+ * According to pagemap_hugetlb_range(), file-backed HugeTLB
+ * page cannot be swapped. So PAGE_IS_FILE hasn't been checked
+ * for swapped pages.
+ */
+ if (pte_present(pte)) {
+ categories |= PAGE_IS_PRESENT;
+ if (!huge_pte_uffd_wp(pte))
+ categories |= PAGE_IS_WRITTEN;
+ if (!PageAnon(pte_page(pte)))
+ categories |= PAGE_IS_FILE;
+ if (is_zero_pfn(pte_pfn(pte)))
+ categories |= PAGE_IS_PFNZERO;
+ } else if (is_swap_pte(pte)) {
+ categories |= PAGE_IS_SWAPPED;
+ if (!pte_swp_uffd_wp_any(pte))
+ categories |= PAGE_IS_WRITTEN;
+ }
+
+ return categories;
+}
+
+static 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));
+}
+#endif /* CONFIG_HUGETLB_PAGE */
+
+static bool pagemap_scan_is_interesting_page(unsigned long categories,
+ const struct pagemap_scan_private *p)
+{
+ categories ^= p->arg.category_inverted;
+ if ((categories & p->arg.category_mask) != p->arg.category_mask)
+ return false;
+ if (p->arg.category_anyof_mask && !(categories & p->arg.category_anyof_mask))
+ return false;
+
+ return true;
+}
+
+static bool pagemap_scan_is_interesting_vma(unsigned long categories,
+ const struct pagemap_scan_private *p)
+{
+ unsigned long required = p->arg.category_mask & PAGE_IS_WPALLOWED;
+
+ categories ^= p->arg.category_inverted;
+ if ((categories & required) != required)
+ return false;
+
+ return true;
+}
+
+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;
+ unsigned long vma_category = 0;
+
+ if (userfaultfd_wp_async(vma) && userfaultfd_wp_use_markers(vma))
+ vma_category |= PAGE_IS_WPALLOWED;
+ else if (p->arg.flags & PM_SCAN_CHECK_WPASYNC)
+ return -EPERM;
+
+ if (vma->vm_flags & VM_PFNMAP)
+ return 1;
+
+ if (!pagemap_scan_is_interesting_vma(vma_category, p))
+ return 1;
+
+ p->cur_vma_category = vma_category;
+
+ return 0;
+}
+
+static bool pagemap_scan_push_range(unsigned long categories,
+ struct pagemap_scan_private *p,
+ unsigned long addr, unsigned long end)
+{
+ struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
+
+ /*
+ * When there is no output buffer provided at all, the sentinel values
+ * won't match here. There is no other way for `cur_buf->end` to be
+ * non-zero other than it being non-empty.
+ */
+ if (addr == cur_buf->end && categories == cur_buf->categories) {
+ cur_buf->end = end;
+ return true;
+ }
+
+ if (cur_buf->end) {
+ if (p->vec_buf_index >= p->vec_buf_len - 1)
+ return false;
+
+ cur_buf = &p->vec_buf[++p->vec_buf_index];
+ }
+
+ cur_buf->start = addr;
+ cur_buf->end = end;
+ cur_buf->categories = categories;
+
+ return true;
+}
+
+static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
+ unsigned long addr, unsigned long end)
+{
+ struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
+
+ if (cur_buf->start != addr) {
+ cur_buf->end = addr;
+ } else {
+ cur_buf->start = cur_buf->end = 0;
+ if (p->vec_buf_index > 0)
+ p->vec_buf_index--;
+ }
+
+ p->found_pages -= (end - addr) / PAGE_SIZE;
+}
+
+static int pagemap_scan_output(unsigned long categories,
+ struct pagemap_scan_private *p,
+ unsigned long addr, unsigned long *end)
+{
+ unsigned long n_pages, total_pages;
+ int ret = 0;
+
+ if (!p->vec_buf)
+ return 0;
+
+ categories &= p->arg.return_mask;
+
+ n_pages = (*end - addr) / PAGE_SIZE;
+ if (check_add_overflow(p->found_pages, n_pages, &total_pages) ||
+ total_pages > p->arg.max_pages) {
+ size_t n_too_much = total_pages - p->arg.max_pages;
+ *end -= n_too_much * PAGE_SIZE;
+ n_pages -= n_too_much;
+ ret = -ENOSPC;
+ }
+
+ if (!pagemap_scan_push_range(categories, p, addr, *end)) {
+ *end = addr;
+ n_pages = 0;
+ ret = -ENOSPC;
+ }
+
+ p->found_pages += n_pages;
+ if (ret)
+ p->walk_end_addr = *end;
+
+ return ret;
+}
+
+static int pagemap_scan_thp_entry(pmd_t *pmd, unsigned long start,
+ unsigned long end, struct mm_walk *walk)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ struct pagemap_scan_private *p = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ unsigned long categories;
+ spinlock_t *ptl;
+ int ret = 0;
+
+ ptl = pmd_trans_huge_lock(pmd, vma);
+ if (!ptl)
+ return -ENOENT;
+
+ categories = p->cur_vma_category | pagemap_thp_category(*pmd);
+
+ if (!pagemap_scan_is_interesting_page(categories, p))
+ goto out_unlock;
+
+ ret = pagemap_scan_output(categories, p, start, &end);
+ if (start == end)
+ goto out_unlock;
+
+ if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+ goto out_unlock;
+ if (~categories & PAGE_IS_WRITTEN)
+ goto out_unlock;
+
+ /*
+ * Break huge page into small pages if the WP operation
+ * needs to be performed on a portion of the huge page.
+ */
+ if (end != start + HPAGE_SIZE) {
+ spin_unlock(ptl);
+ split_huge_pmd(vma, pmd, start);
+ pagemap_scan_backout_range(p, start, end);
+ /* Report as if there was no THP */
+ return -ENOENT;
+ }
+
+ make_uffd_wp_pmd(vma, start, pmd);
+ flush_tlb_range(vma, start, end);
+out_unlock:
+ spin_unlock(ptl);
+ return ret;
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE */
+ return -ENOENT;
+#endif
+}
+
+static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
+ unsigned long end, struct mm_walk *walk)
+{
+ struct pagemap_scan_private *p = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ unsigned long addr, flush_end = 0;
+ pte_t *pte, *start_pte;
+ spinlock_t *ptl;
+ int ret;
+
+ arch_enter_lazy_mmu_mode();
+
+ ret = pagemap_scan_thp_entry(pmd, start, end, walk);
+ if (ret != -ENOENT) {
+ arch_leave_lazy_mmu_mode();
+ return ret;
+ }
+
+ ret = 0;
+ start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
+ if (!pte) {
+ arch_leave_lazy_mmu_mode();
+ walk->action = ACTION_AGAIN;
+ return 0;
+ }
+
+ for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
+ unsigned long categories = p->cur_vma_category |
+ pagemap_page_category(p, vma, addr, ptep_get(pte));
+ unsigned long next = addr + PAGE_SIZE;
+
+ if (!pagemap_scan_is_interesting_page(categories, p))
+ continue;
+
+ ret = pagemap_scan_output(categories, p, addr, &next);
+ if (next == addr)
+ break;
+
+ if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+ continue;
+ if (~categories & PAGE_IS_WRITTEN)
+ continue;
+
+ make_uffd_wp_pte(vma, addr, pte);
+ if (!flush_end)
+ start = addr;
+ flush_end = next;
+ }
+
+ if (flush_end)
+ flush_tlb_range(vma, start, addr);
+
+ pte_unmap_unlock(start_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)
+{
+ struct pagemap_scan_private *p = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ unsigned long categories;
+ spinlock_t *ptl;
+ int ret = 0;
+ pte_t pte;
+
+ if (~p->arg.flags & PM_SCAN_WP_MATCHING) {
+ /* Go the short route when not write-protecting pages. */
+
+ pte = huge_ptep_get(ptep);
+ categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
+
+ if (!pagemap_scan_is_interesting_page(categories, p))
+ return 0;
+
+ return pagemap_scan_output(categories, p, start, &end);
+ }
+
+ i_mmap_lock_write(vma->vm_file->f_mapping);
+ ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep);
+
+ pte = huge_ptep_get(ptep);
+ categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
+
+ if (!pagemap_scan_is_interesting_page(categories, p))
+ goto out_unlock;
+
+ ret = pagemap_scan_output(categories, p, start, &end);
+ if (start == end)
+ goto out_unlock;
+
+ if (~categories & PAGE_IS_WRITTEN)
+ goto out_unlock;
+
+ if (end != start + HPAGE_SIZE) {
+ /* Partial HugeTLB page WP isn't possible. */
+ pagemap_scan_backout_range(p, start, end);
+ p->walk_end_addr = start;
+ ret = 0;
+ goto out_unlock;
+ }
+
+ make_uffd_wp_huge_pte(vma, start, ptep, pte);
+ flush_hugetlb_tlb_range(vma, start, end);
+
+out_unlock:
+ 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)
+{
+ struct pagemap_scan_private *p = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ int ret, err;
+
+ if (!vma || !pagemap_scan_is_interesting_page(p->cur_vma_category, p))
+ return 0;
+
+ ret = pagemap_scan_output(p->cur_vma_category, p, addr, &end);
+ if (addr == end)
+ return ret;
+
+ if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+ return ret;
+
+ err = uffd_wp_range(vma, addr, end - addr, true);
+ if (err < 0)
+ ret = err;
+
+ 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_get_args(struct pm_scan_arg *arg,
+ unsigned long uarg)
+{
+ if (copy_from_user(arg, (void __user *)uarg, sizeof(*arg)))
+ return -EFAULT;
+
+ if (arg->size != sizeof(struct pm_scan_arg))
+ return -EINVAL;
+
+ /* Validate requested features */
+ if (arg->flags & ~PM_SCAN_FLAGS)
+ return -EINVAL;
+ if ((arg->category_inverted | arg->category_mask |
+ arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES)
+ return -EINVAL;
+
+ arg->start = untagged_addr((unsigned long)arg->start);
+ arg->end = untagged_addr((unsigned long)arg->end);
+ arg->vec = untagged_addr((unsigned long)arg->vec);
+
+ /* Validate memory pointers */
+ if (!IS_ALIGNED(arg->start, PAGE_SIZE))
+ return -EINVAL;
+ if (!access_ok((void __user *)arg->start, arg->end - arg->start))
+ return -EFAULT;
+ if (!arg->vec && arg->vec_len)
+ return -EINVAL;
+ if (arg->vec && !access_ok((void __user *)arg->vec,
+ arg->vec_len * sizeof(struct page_region)))
+ return -EFAULT;
+
+ /* Fixup default values */
+ arg->end = ALIGN(arg->end, PAGE_SIZE);
+ if (!arg->max_pages)
+ arg->max_pages = ULONG_MAX;
+
+ return 0;
+}
+
+static int pagemap_scan_writeback_args(struct pm_scan_arg *arg,
+ unsigned long uargl)
+{
+ struct pm_scan_arg __user *uarg = (void __user *)uargl;
+
+ if (copy_to_user(&uarg->walk_end, &arg->walk_end, sizeof(arg->walk_end)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static int pagemap_scan_init_bounce_buffer(struct pagemap_scan_private *p)
+{
+ if (!p->arg.vec_len)
+ return 0;
+
+ /*
+ * Allocate a smaller buffer to get output from inside the page
+ * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks.
+ */
+ p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,
+ p->arg.vec_len);
+ p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),
+ GFP_KERNEL);
+ if (!p->vec_buf)
+ return -ENOMEM;
+
+ p->vec_buf[0].end = 0;
+ p->vec_out = (struct page_region __user *)p->arg.vec;
+
+ return 0;
+}
+
+static int pagemap_scan_flush_buffer(struct pagemap_scan_private *p)
+{
+ const struct page_region *buf = p->vec_buf;
+ int n = (int)p->vec_buf_index;
+
+ if (p->arg.vec_len == 0)
+ return 0;
+
+ if (buf[n].end && buf[n].end != buf[n].start)
+ n++;
+
+ if (!n)
+ return 0;
+
+ if (copy_to_user(p->vec_out, buf, n * sizeof(*buf)))
+ return -EFAULT;
+
+ p->arg.vec_len -= n;
+ p->vec_out += n;
+
+ p->vec_buf_index = 0;
+ p->vec_buf_len = min_t(size_t, p->vec_buf_len, p->arg.vec_len);
+ p->vec_buf[0].end = 0;
+
+ return n;
+}
+
+static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
+{
+ struct mmu_notifier_range range;
+ struct pagemap_scan_private p = {0};
+ unsigned long walk_start;
+ size_t n_ranges_out = 0;
+ int ret;
+
+ ret = pagemap_scan_get_args(&p.arg, uarg);
+ if (ret)
+ return ret;
+
+ p.masks_of_interest = p.arg.category_inverted | p.arg.category_mask |
+ p.arg.category_anyof_mask | p.arg.return_mask;
+ ret = pagemap_scan_init_bounce_buffer(&p);
+ if (ret)
+ return ret;
+
+ /* Protection change for the range is going to happen. */
+ if (p.arg.flags & PM_SCAN_WP_MATCHING) {
+ mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
+ mm, p.arg.start, p.arg.end);
+ mmu_notifier_invalidate_range_start(&range);
+ }
+
+ for (walk_start = p.arg.start; walk_start < p.arg.end;
+ walk_start = p.arg.walk_end) {
+ int n_out;
+
+ if (fatal_signal_pending(current)) {
+ ret = -EINTR;
+ break;
+ }
+
+ ret = mmap_read_lock_killable(mm);
+ if (ret)
+ break;
+ ret = walk_page_range(mm, walk_start, p.arg.end,
+ &pagemap_scan_ops, &p);
+ mmap_read_unlock(mm);
+
+ n_out = pagemap_scan_flush_buffer(&p);
+ if (n_out < 0)
+ ret = n_out;
+ else
+ n_ranges_out += n_out;
+
+ p.walk_end_addr = p.walk_end_addr ? p.walk_end_addr : p.arg.end;
+
+ if (ret != -ENOSPC || p.arg.vec_len == 0 ||
+ p.found_pages == p.arg.max_pages)
+ break;
+ }
+
+ /* ENOSPC signifies early stop (buffer full) from the walk. */
+ if (!ret || ret == -ENOSPC)
+ ret = n_ranges_out;
+
+ p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : walk_start;
+ if (pagemap_scan_writeback_args(&p.arg, uarg))
+ ret = -EFAULT;
+
+ if (p.arg.flags & PM_SCAN_WP_MATCHING)
+ 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 0a393bc02f25b..8f8ff07453f22 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 b7b56871029c5..0202af0434791 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -305,4 +305,63 @@ 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)
+
+/* Bitmasks provided in pm_scan_args masks and reported in page_region.categories. */
+#define PAGE_IS_WPALLOWED (1 << 0)
+#define PAGE_IS_WRITTEN (1 << 1)
+#define PAGE_IS_FILE (1 << 2)
+#define PAGE_IS_PRESENT (1 << 3)
+#define PAGE_IS_SWAPPED (1 << 4)
+#define PAGE_IS_PFNZERO (1 << 5)
+#define PAGE_IS_HUGE (1 << 6)
+
+/*
+ * struct page_region - Page region with flags
+ * @start: Start of the region
+ * @end: End of the region (exclusive)
+ * @categories: PAGE_IS_* category bitmask for the region
+ */
+struct page_region {
+ __u64 start;
+ __u64 end;
+ __u64 categories;
+};
+
+/* Flags for PAGEMAP_SCAN ioctl */
+#define PM_SCAN_WP_MATCHING (1 << 0) /* Write protect the pages matched. */
+#define PM_SCAN_CHECK_WPASYNC (1 << 1) /* Abort the scan when a non-WP-enabled page is found. */
+
+/*
+ * struct pm_scan_arg - Pagemap ioctl argument
+ * @size: Size of the structure
+ * @flags: Flags for the IOCTL
+ * @start: Starting address of the region
+ * @end: Ending address of the region
+ * @walk_end Address where the scan stopped (written by kernel).
+ * walk_end == end (tag removed) informs that the scan completed on entire range.
+ * @vec: Address of page_region struct array for output
+ * @vec_len: Length of the page_region struct array
+ * @max_pages: Optional limit for number of returned pages (0 = disabled)
+ * @category_inverted: PAGE_IS_* categories which values match if 0 instead of 1
+ * @category_mask: Skip pages for which any category doesn't match
+ * @category_anyof_mask: Skip pages for which no category matches
+ * @return_mask: PAGE_IS_* categories that are to be reported in `page_region`s returned
+ */
+struct pm_scan_arg {
+ __u64 size;
+ __u64 flags;
+ __u64 start;
+ __u64 end;
+ __u64 walk_end;
+ __u64 vec;
+ __u64 vec_len;
+ __u64 max_pages;
+ __u64 category_inverted;
+ __u64 category_mask;
+ __u64 category_anyof_mask;
+ __u64 return_mask;
+};
+
#endif /* _UAPI_LINUX_FS_H */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a073e6ed8900b..3b07db0a4f2d9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5008,7 +5008,7 @@ 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;
--
2.40.1
On Fri, Aug 11, 2023 at 11:08:38PM +0500, Muhammad Usama Anjum wrote:
> The PAGEMAP_SCAN IOCTL on the pagemap file can be used to get or optionally
> clear the info about page table entries. The following operations are supported
> in this IOCTL:
> - Scan the address range and get the memory ranges matching the provided criteria.
> This is performed by default when the output buffer is specified.
Nit: This is actually performed always, but you can disable the output part
by passing {NULL, 0} for the buffer.
[...]
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -19,6 +19,8 @@
> #include <linux/shmem_fs.h>
> #include <linux/uaccess.h>
> #include <linux/pkeys.h>
> +#include <linux/minmax.h>
> +#include <linux/overflow.h>
>
> #include <asm/elf.h>
> #include <asm/tlb.h>
> @@ -1749,11 +1751,682 @@ static int pagemap_release(struct inode *inode, struct file *file)
> return 0;
> }
>
> +#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
> + PAGE_IS_FILE | PAGE_IS_PRESENT | \
> + PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
> + PAGE_IS_HUGE)
> +#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
> +
> +struct pagemap_scan_private {
> + struct pm_scan_arg arg;
> + unsigned long masks_of_interest, cur_vma_category;
> + struct page_region *vec_buf;
> + unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
> + struct page_region __user *vec_out;
> +};
[...]
> +static unsigned long pagemap_thp_category(pmd_t pmd)
> +{
> + unsigned long categories = PAGE_IS_HUGE;
> +
> + /*
> + * THPs don't support file-backed memory. So PAGE_IS_FILE
> + * hasn't been checked here.
"hasn't been" -> "is not"
(same for HugeTLB comment)
> +static bool pagemap_scan_push_range(unsigned long categories,
> + struct pagemap_scan_private *p,
> + unsigned long addr, unsigned long end)
> +{
> + struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
> +
> + /*
> + * When there is no output buffer provided at all, the sentinel values
> + * won't match here. There is no other way for `cur_buf->end` to be
> + * non-zero other than it being non-empty.
> + */
> + if (addr == cur_buf->end && categories == cur_buf->categories) {
> + cur_buf->end = end;
> + return true;
> + }
> +
> + if (cur_buf->end) {
> + if (p->vec_buf_index >= p->vec_buf_len - 1)
> + return false;
> +
> + cur_buf = &p->vec_buf[++p->vec_buf_index];
> + }
> +
> + cur_buf->start = addr;
> + cur_buf->end = end;
> + cur_buf->categories = categories;
> +
> + return true;
> +}
> +
> +static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
> + unsigned long addr, unsigned long end)
> +{
> + struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
> +
> + if (cur_buf->start != addr) {
> + cur_buf->end = addr;
> + } else {
> + cur_buf->start = cur_buf->end = 0;
> + if (p->vec_buf_index > 0)
> + p->vec_buf_index--;
There is no need to move to the previous index, as if the walk ends at
this moment, the flush_buffer() code will ignore the empty last range.
> + }
> +
> + p->found_pages -= (end - addr) / PAGE_SIZE;
> +}
> +
> +static int pagemap_scan_output(unsigned long categories,
> + struct pagemap_scan_private *p,
> + unsigned long addr, unsigned long *end)
> +{
> + unsigned long n_pages, total_pages;
> + int ret = 0;
> +
> + if (!p->vec_buf)
> + return 0;
> +
> + categories &= p->arg.return_mask;
> +
> + n_pages = (*end - addr) / PAGE_SIZE;
> + if (check_add_overflow(p->found_pages, n_pages, &total_pages) ||
> + total_pages > p->arg.max_pages) {
> + size_t n_too_much = total_pages - p->arg.max_pages;
> + *end -= n_too_much * PAGE_SIZE;
> + n_pages -= n_too_much;
> + ret = -ENOSPC;
> + }
> +
> + if (!pagemap_scan_push_range(categories, p, addr, *end)) {
> + *end = addr;
> + n_pages = 0;
> + ret = -ENOSPC;
> + }
> +
> + p->found_pages += n_pages;
> + if (ret)
> + p->walk_end_addr = *end;
> +
> + return ret;
> +}
[...]
> +static int pagemap_scan_init_bounce_buffer(struct pagemap_scan_private *p)
> +{
> + if (!p->arg.vec_len)
> + return 0;
The removal of `cur_buf` lost the case of empty non-NULL output buffer
passed in args. That was requesting the walk to stop at first matching
page (with the address returned in `walk_end`). The push_range() call
is still checking that, but since neither the buffer nor the sentinel
values are set, the case is not possible to invoke.
> + /*
> + * Allocate a smaller buffer to get output from inside the page
> + * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks.
> + */
I think this is no longer true? We can now allocate arbitrary number of
entries, but should probably have at least 512 to cover one PMD of pages.
So it would be better to have a constant that holds the number of
entries in the bounce buffer.
> + p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,
> + p->arg.vec_len);
> + p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),
> + GFP_KERNEL);
> + if (!p->vec_buf)
> + return -ENOMEM;
> +
> + p->vec_buf[0].end = 0;
p->vec_buf->start = p->vec_buf->end = 0;
> + p->vec_out = (struct page_region __user *)p->arg.vec;
> +
> + return 0;
> +}
> +
> +static int pagemap_scan_flush_buffer(struct pagemap_scan_private *p)
> +{
> + const struct page_region *buf = p->vec_buf;
> + int n = (int)p->vec_buf_index;
Why do you need an `int` here (requiring a cast)?
> + if (p->arg.vec_len == 0)
> + return 0;
This should be actually `if (!buf)` as this notes that we don't have any
buffer allocated (due to no output requested).
> + if (buf[n].end && buf[n].end != buf[n].start)
> + n++;
Testing `buf[n].end` is redundant, as the range is nonempty if
`end != start`.
> + if (!n)
> + return 0;
> +
> + if (copy_to_user(p->vec_out, buf, n * sizeof(*buf)))
> + return -EFAULT;
> +
> + p->arg.vec_len -= n;
> + p->vec_out += n;
> +
> + p->vec_buf_index = 0;
> + p->vec_buf_len = min_t(size_t, p->vec_buf_len, p->arg.vec_len);
> + p->vec_buf[0].end = 0;
buf->start = buf->end = 0;
> + return n;
> +}
> +
> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
> +{
> + struct mmu_notifier_range range;
> + struct pagemap_scan_private p = {0};
> + unsigned long walk_start;
> + size_t n_ranges_out = 0;
> + int ret;
> +
> + ret = pagemap_scan_get_args(&p.arg, uarg);
> + if (ret)
> + return ret;
> +
> + p.masks_of_interest = p.arg.category_inverted | p.arg.category_mask |
> + p.arg.category_anyof_mask | p.arg.return_mask;
`category_inverted` can be left out, because if a set bit it is not also in one
of the masks, then its value is going to be ignored.
[...]
> + for (walk_start = p.arg.start; walk_start < p.arg.end;
> + walk_start = p.arg.walk_end) {
> + int n_out;
> +
> + if (fatal_signal_pending(current)) {
> + ret = -EINTR;
> + break;
> + }
> +
> + ret = mmap_read_lock_killable(mm);
> + if (ret)
> + break;
> + ret = walk_page_range(mm, walk_start, p.arg.end,
> + &pagemap_scan_ops, &p);
> + mmap_read_unlock(mm);
> +
> + n_out = pagemap_scan_flush_buffer(&p);
> + if (n_out < 0)
> + ret = n_out;
> + else
> + n_ranges_out += n_out;
> +
> + p.walk_end_addr = p.walk_end_addr ? p.walk_end_addr : p.arg.end;
Why is `p.walk_end_addr` needed? It is not used in the loop code. Shoudn't
it be `p.arg.walk_end` as used in the `for` loop continuation statement?
> + if (ret != -ENOSPC || p.arg.vec_len == 0 ||
> + p.found_pages == p.arg.max_pages)
> + break;
Nit: I think you could split this into two or three separate `if (x)
break;` for easier reading. The `vec_len` and `found_pages` are
buffer-full tests, so could go along, but `ret != ENOSPC` is checking an
error condition aborting the scan before it ends.
> + }
> +
> + /* ENOSPC signifies early stop (buffer full) from the walk. */
> + if (!ret || ret == -ENOSPC)
> + ret = n_ranges_out;
> +
> + p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : walk_start;
> + if (pagemap_scan_writeback_args(&p.arg, uarg))
> + ret = -EFAULT;
[...]
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
[...]
> +/*
> + * struct pm_scan_arg - Pagemap ioctl argument
> + * @size: Size of the structure
> + * @flags: Flags for the IOCTL
> + * @start: Starting address of the region
> + * @end: Ending address of the region
> + * @walk_end Address where the scan stopped (written by kernel).
> + * walk_end == end (tag removed) informs that the scan completed on entire range.
I'm not sure `tag removed` is enough to know what tag was removed.
Maybe something like "with address tags cleared" would fit?
Best Regards
Micha? Miros?aw
On 8/12/23 8:49 PM, Michał Mirosław wrote:
> On Fri, Aug 11, 2023 at 11:08:38PM +0500, Muhammad Usama Anjum wrote:
>> The PAGEMAP_SCAN IOCTL on the pagemap file can be used to get or optionally
>> clear the info about page table entries. The following operations are supported
>> in this IOCTL:
>> - Scan the address range and get the memory ranges matching the provided criteria.
>> This is performed by default when the output buffer is specified.
>
> Nit: This is actually performed always, but you can disable the output part
> by passing {NULL, 0} for the buffer.
I'll update it to:
"This is performed when the output buffer is specified."
>
> [...]
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -19,6 +19,8 @@
>> #include <linux/shmem_fs.h>
>> #include <linux/uaccess.h>
>> #include <linux/pkeys.h>
>> +#include <linux/minmax.h>
>> +#include <linux/overflow.h>
>>
>> #include <asm/elf.h>
>> #include <asm/tlb.h>
>> @@ -1749,11 +1751,682 @@ static int pagemap_release(struct inode *inode, struct file *file)
>> return 0;
>> }
>>
>> +#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
>> + PAGE_IS_FILE | PAGE_IS_PRESENT | \
>> + PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
>> + PAGE_IS_HUGE)
>> +#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
>> +
>> +struct pagemap_scan_private {
>> + struct pm_scan_arg arg;
>> + unsigned long masks_of_interest, cur_vma_category;
>> + struct page_region *vec_buf;
>> + unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
>> + struct page_region __user *vec_out;
>> +};
> [...]
>> +static unsigned long pagemap_thp_category(pmd_t pmd)
>> +{
>> + unsigned long categories = PAGE_IS_HUGE;
>> +
>> + /*
>> + * THPs don't support file-backed memory. So PAGE_IS_FILE
>> + * hasn't been checked here.
>
> "hasn't been" -> "is not"
> (same for HugeTLB comment)
I'll update.
>
>> +static bool pagemap_scan_push_range(unsigned long categories,
>> + struct pagemap_scan_private *p,
>> + unsigned long addr, unsigned long end)
>> +{
>> + struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
>> +
>> + /*
>> + * When there is no output buffer provided at all, the sentinel values
>> + * won't match here. There is no other way for `cur_buf->end` to be
>> + * non-zero other than it being non-empty.
>> + */
>> + if (addr == cur_buf->end && categories == cur_buf->categories) {
>> + cur_buf->end = end;
>> + return true;
>> + }
>> +
>> + if (cur_buf->end) {
>> + if (p->vec_buf_index >= p->vec_buf_len - 1)
>> + return false;
>> +
>> + cur_buf = &p->vec_buf[++p->vec_buf_index];
>> + }
>> +
>> + cur_buf->start = addr;
>> + cur_buf->end = end;
>> + cur_buf->categories = categories;
>> +
>> + return true;
>> +}
>> +
>> +static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
>> + unsigned long addr, unsigned long end)
>> +{
>> + struct page_region *cur_buf = &p->vec_buf[p->vec_buf_index];
>> +
>> + if (cur_buf->start != addr) {
>> + cur_buf->end = addr;
>> + } else {
>> + cur_buf->start = cur_buf->end = 0;
>> + if (p->vec_buf_index > 0)
>> + p->vec_buf_index--;
>
> There is no need to move to the previous index, as if the walk ends at
> this moment, the flush_buffer() code will ignore the empty last range.
Yeah, I'll update.
>
>> + }
>> +
>> + p->found_pages -= (end - addr) / PAGE_SIZE;
>> +}
>> +
>> +static int pagemap_scan_output(unsigned long categories,
>> + struct pagemap_scan_private *p,
>> + unsigned long addr, unsigned long *end)
>> +{
>> + unsigned long n_pages, total_pages;
>> + int ret = 0;
>> +
>> + if (!p->vec_buf)
>> + return 0;
>> +
>> + categories &= p->arg.return_mask;
>> +
>> + n_pages = (*end - addr) / PAGE_SIZE;
>> + if (check_add_overflow(p->found_pages, n_pages, &total_pages) ||
>> + total_pages > p->arg.max_pages) {
>> + size_t n_too_much = total_pages - p->arg.max_pages;
>> + *end -= n_too_much * PAGE_SIZE;
>> + n_pages -= n_too_much;
>> + ret = -ENOSPC;
>> + }
>> +
>> + if (!pagemap_scan_push_range(categories, p, addr, *end)) {
>> + *end = addr;
>> + n_pages = 0;
>> + ret = -ENOSPC;
>> + }
>> +
>> + p->found_pages += n_pages;
>> + if (ret)
>> + p->walk_end_addr = *end;
>> +
>> + return ret;
>> +}
> [...]
>> +static int pagemap_scan_init_bounce_buffer(struct pagemap_scan_private *p)
>> +{
>> + if (!p->arg.vec_len)
>> + return 0;
>
> The removal of `cur_buf` lost the case of empty non-NULL output buffer
> passed in args. That was requesting the walk to stop at first matching
> page (with the address returned in `walk_end`). The push_range() call
> is still checking that, but since neither the buffer nor the sentinel
> values are set, the case is not possible to invoke.
Yeah, this is why I've removed all that logic here. The vec_len is set to 0
and vec_buf to NULL. This handles all the cases.
>
>> + /*
>> + * Allocate a smaller buffer to get output from inside the page
>> + * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks.
>> + */
>
> I think this is no longer true? We can now allocate arbitrary number of
> entries, but should probably have at least 512 to cover one PMD of pages.
> So it would be better to have a constant that holds the number of
> entries in the bounce buffer.
I'll remove the comment. PAGEMAP_WALK_SIZE >> PAGE_SHIFT is a constant
already, just a fancy one.
Altough if we can increase 512 to bigger number, it'll be better in terms
of performance. I'm not sure how much we can increase it.
>
>> + p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,
>> + p->arg.vec_len);
>> + p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),
>> + GFP_KERNEL);
>> + if (!p->vec_buf)
>> + return -ENOMEM;
>> +
>> + p->vec_buf[0].end = 0;
>
> p->vec_buf->start = p->vec_buf->end = 0;
Sure.
>
>> + p->vec_out = (struct page_region __user *)p->arg.vec;
>> +
>> + return 0;
>> +}
>> +
>> +static int pagemap_scan_flush_buffer(struct pagemap_scan_private *p)
>> +{
>> + const struct page_region *buf = p->vec_buf;
>> + int n = (int)p->vec_buf_index;
>
> Why do you need an `int` here (requiring a cast)?
Just looked at it, n and return code of pagemap_scan_flush_buffer() should
be long. Changed.
>
>> + if (p->arg.vec_len == 0)
>> + return 0;
>
> This should be actually `if (!buf)` as this notes that we don't have any
> buffer allocated (due to no output requested).
I'll update. !buf seems more reasonable.
>
>> + if (buf[n].end && buf[n].end != buf[n].start)
>> + n++;
>
> Testing `buf[n].end` is redundant, as the range is nonempty if
> `end != start`.
Sure.
>
>> + if (!n)
>> + return 0;
>> +
>> + if (copy_to_user(p->vec_out, buf, n * sizeof(*buf)))
>> + return -EFAULT;
>> +
>> + p->arg.vec_len -= n;
>> + p->vec_out += n;
>> +
>> + p->vec_buf_index = 0;
>> + p->vec_buf_len = min_t(size_t, p->vec_buf_len, p->arg.vec_len);
>> + p->vec_buf[0].end = 0;
>
> buf->start = buf->end = 0;
Sure.
>
>> + return n;
>> +}
>> +
>> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
>> +{
>> + struct mmu_notifier_range range;
>> + struct pagemap_scan_private p = {0};
>> + unsigned long walk_start;
>> + size_t n_ranges_out = 0;
>> + int ret;
>> +
>> + ret = pagemap_scan_get_args(&p.arg, uarg);
>> + if (ret)
>> + return ret;
>> +
>> + p.masks_of_interest = p.arg.category_inverted | p.arg.category_mask |
>> + p.arg.category_anyof_mask | p.arg.return_mask;
>
> `category_inverted` can be left out, because if a set bit it is not also in one
> of the masks, then its value is going to be ignored.
Okay.
>
> [...]
>> + for (walk_start = p.arg.start; walk_start < p.arg.end;
>> + walk_start = p.arg.walk_end) {
>> + int n_out;
>> +
>> + if (fatal_signal_pending(current)) {
>> + ret = -EINTR;
>> + break;
>> + }
>> +
>> + ret = mmap_read_lock_killable(mm);
>> + if (ret)
>> + break;
>> + ret = walk_page_range(mm, walk_start, p.arg.end,
>> + &pagemap_scan_ops, &p);
>> + mmap_read_unlock(mm);
>> +
>> + n_out = pagemap_scan_flush_buffer(&p);
>> + if (n_out < 0)
>> + ret = n_out;
>> + else
>> + n_ranges_out += n_out;
>> +
>> + p.walk_end_addr = p.walk_end_addr ? p.walk_end_addr : p.arg.end;
>
> Why is `p.walk_end_addr` needed? It is not used in the loop code. Shoudn't
> it be `p.arg.walk_end` as used in the `for` loop continuation statement?
It isn't needed for the loop. But we need to note down the ending address
of walk. We can switch to using p.arg.walk_end for better logical reason.
I'll update code.
>
>> + if (ret != -ENOSPC || p.arg.vec_len == 0 ||
>> + p.found_pages == p.arg.max_pages)
>> + break;
>
> Nit: I think you could split this into two or three separate `if (x)
> break;` for easier reading. The `vec_len` and `found_pages` are
> buffer-full tests, so could go along, but `ret != ENOSPC` is checking an
> error condition aborting the scan before it ends.
Can be done.
>
>> + }
>> +
>> + /* ENOSPC signifies early stop (buffer full) from the walk. */
>> + if (!ret || ret == -ENOSPC)
>> + ret = n_ranges_out;
>> +
>> + p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : walk_start;
>> + if (pagemap_scan_writeback_args(&p.arg, uarg))
>> + ret = -EFAULT;
> [...]
>> --- a/include/uapi/linux/fs.h
>> +++ b/include/uapi/linux/fs.h
> [...]
>> +/*
>> + * struct pm_scan_arg - Pagemap ioctl argument
>> + * @size: Size of the structure
>> + * @flags: Flags for the IOCTL
>> + * @start: Starting address of the region
>> + * @end: Ending address of the region
>> + * @walk_end Address where the scan stopped (written by kernel).
>> + * walk_end == end (tag removed) informs that the scan completed on entire range.
>
> I'm not sure `tag removed` is enough to know what tag was removed.
> Maybe something like "with address tags cleared" would fit?
Okay.
>
> Best Regards
> Michał Mirosław
--
BR,
Muhammad Usama Anjum