Commit 2c1f057e authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

fs/proc/task_mmu: properly detect PM_MMAP_EXCLUSIVE per page of PMD-mapped THPs 

We added PM_MMAP_EXCLUSIVE in 2015 via commit 77bb499b ("pagemap: add
mmap-exclusive bit for marking pages mapped only here"), when THPs could
not be partially mapped and page_mapcount() returned something that was
true for all pages of the THP.

In 2016, we added support for partially mapping THPs via commit
53f9263b ("mm: rework mapcount accounting to enable 4k mapping of
THPs") but missed to determine PM_MMAP_EXCLUSIVE as well per page.

Checking page_mapcount() on the head page does not tell the whole story.

We should check each individual page.  In a future without per-page
mapcounts it will be different, but we'll change that to be consistent
with PTE-mapped THPs once we deal with that.

Link: https://lkml.kernel.org/r/20240607122357.115423-4-david@redhat.com


Fixes: 53f9263b ("mm: rework mapcount accounting to enable 4k mapping of THPs")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <ioworker0@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent da7f31ed

fs/proc/task_mmu.c

+12 −10
Original line number Diff line number Diff line
@@ -1477,6 +1477,7 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, 


	ptl = pmd_trans_huge_lock(pmdp, vma);

	if (ptl) {

		unsigned int idx = (addr & ~PMD_MASK) >> PAGE_SHIFT;

		u64 flags = 0, frame = 0;

		pmd_t pmd = *pmdp;

		struct page *page = NULL;
@@ -1493,8 +1494,7 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, 
			if (pmd_uffd_wp(pmd))

				flags |= PM_UFFD_WP;

			if (pm->show_pfn)

				frame = pmd_pfn(pmd) +

					((addr & ~PMD_MASK) >> PAGE_SHIFT);

				frame = pmd_pfn(pmd) + idx;

		}

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION

		else if (is_swap_pmd(pmd)) {
@@ -1503,11 +1503,9 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, 


			if (pm->show_pfn) {

				if (is_pfn_swap_entry(entry))

					offset = swp_offset_pfn(entry);

					offset = swp_offset_pfn(entry) + idx;

				else

					offset = swp_offset(entry);

				offset = offset +

					((addr & ~PMD_MASK) >> PAGE_SHIFT);

					offset = swp_offset(entry) + idx;

				frame = swp_type(entry) |

					(offset << MAX_SWAPFILES_SHIFT);

			}
@@ -1523,12 +1521,16 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, 


		if (page && !PageAnon(page))

			flags |= PM_FILE;

		if (page && (flags & PM_PRESENT) && page_mapcount(page) == 1)

			flags |= PM_MMAP_EXCLUSIVE;



		for (; addr != end; addr += PAGE_SIZE) {

			pagemap_entry_t pme = make_pme(frame, flags);

		for (; addr != end; addr += PAGE_SIZE, idx++) {

			unsigned long cur_flags = flags;

			pagemap_entry_t pme;



			if (page && (flags & PM_PRESENT) &&

			    page_mapcount(page + idx) == 1)

				cur_flags |= PM_MMAP_EXCLUSIVE;



			pme = make_pme(frame, cur_flags);

			err = add_to_pagemap(&pme, pm);

			if (err)

				break;