Re: [PATCH v26 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

On 8/3/23 8:08 PM, Andrei Vagin wrote:

On Thu, Jul 27, 2023 at 02:36:34PM +0500, Muhammad Usama Anjum wrote:

<snip>

...

+static void pagemap_scan_backout_range(struct pagemap_scan_private *p,

• 		       unsigned long addr, unsigned long end,
  

• 		       unsigned long end_addr)
  

It hard to figure out what difference between end and end_addr. I would add a comment here.

I'll fix these in next version.

...

+{

• struct page_region *cur_buf = &p->cur_buf;
• if (cur_buf->start != addr)

• cur_buf->end = addr;
  

• else

• cur_buf->start = cur_buf->end = 0;
  

• p->end_addr = end_addr;
• 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 (!pagemap_scan_is_interesting_page(categories, p)) {

• *end = addr;
  

• return 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) {
  

why do we need to use check_add_overflow here?

...

• size_t n_too_much = total_pages - p->arg.max_pages;
  

it is unsafe to use total_pages if check_add_overflow returns non-zero.

...

• *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->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);
• 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
  

• * need to be performed is 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, 0);
  

pagemap_scan_backout_range looks "weird"... imho, it makes the code harder for understanding.

...

• return -ENOENT;
  

I think you need to add a comment that this ENOENT is a special case.

...

• }
• 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;
• pte_t *pte, *start_pte;
• unsigned long addr;
• bool flush = false;
• 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;
  

• }
• 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(vma, addr, ptep_get(pte));
  

• unsigned long next = addr + PAGE_SIZE;
  

• ret = pagemap_scan_output(categories, p, addr, &next);
  

• if (next == addr) {
  

• 	if (!ret)
  

• 		continue;
  

• 	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) {
  

• 	start = addr;
  

• 	flush = true;
  

• }
  

• }
• if (flush)

• 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);
  

• 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);
• 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, start);
  

• ret = -EINVAL;
  

Why is it EINVAL in this case?

...

• 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)

• 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 -EFAULT;
  

• 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) {

• /*
  

•  * An arbitrary non-page-aligned sentinel value for
  

•  * pagemap_scan_push_range().
  

•  */
  

• p->cur_buf.start = p->cur_buf.end = ULLONG_MAX;
  

• if (p->arg.vec)
  

• 	p->vec_buf = ZERO_SIZE_PTR;
  

• return 0;
  

• }
• /*

• * Allocate a smaller buffer to get output from inside the page
  

• * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks.
  

• * The last range is always stored in p.cur_buf to allow coalescing
  

• * consecutive ranges that have the same categories returned across
  

• * walk_page_range() calls.
  

• */
  

• p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,

• 	       p->arg.vec_len - 1);
  

• p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),

• 		   GFP_KERNEL);
  

• if (!p->vec_buf)

• return -ENOMEM;
  

• 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 (!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 - 1);
• return n;

+}

+static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) +{

• unsigned long walk_start, walk_end;
• struct mmu_notifier_range range;
• struct pagemap_scan_private p;
• size_t n_ranges_out = 0;
• int ret;
• memset(&p, 0, sizeof(p));
• ret = pagemap_scan_get_args(&p.arg, uarg);
• if (ret)

• return ret;
  

• 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);
  

• }
• walk_start = walk_end = p.arg.start;
• for (; walk_end != p.arg.end; walk_start = walk_end) {

• int n_out;
  

• walk_end = min_t(unsigned long,
  

• 		 (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK,
  

• 		 p.arg.end);
  

if (fatal_signal_pending(current)) { ret = EINTR; break; }

...

• ret = mmap_read_lock_killable(mm);
  

• if (ret)
  

• 	break;
  

• ret = walk_page_range(mm, walk_start, walk_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;
  

• if (ret)
  

• 	break;
  

• }
• if (p.cur_buf.start != p.cur_buf.end) {

• if (copy_to_user(p.vec_out, &p.cur_buf, sizeof(p.cur_buf)))
  

• 	ret = -EFAULT;
  

• else
  

• 	++n_ranges_out;
  

• }
• /* ENOSPC signifies early stop (buffer full) from the walk. */
• if (!ret || ret == -ENOSPC)

• ret = n_ranges_out;
  

• p.arg.walk_end = p.end_addr ? p.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..1bb3c625c2381 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -305,4 +305,62 @@ 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_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)

+/*

• • 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: Ending address of the visited memory is returned

• • 	(This helps if entire range hasn't been visited)
    

• • @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; -- 2.39.2