[PATCH v1 3/6] fs/proc/task_mmu: properly detect PM_MMAP_EXCLUSIVE per page of PMD-mapped THPs

David Hildenbrand
2024-06-07T12:24:12Z

We added PM_MMAP_EXCLUSIVE in 2015 via commit 77bb499bb60f ("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 53f9263baba6 ("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.

Fixes: 53f9263baba6 ("mm: rework mapcount accounting to enable 4k mapping of THPs")
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
fs/proc/task_mmu.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 40e38bc33a9d2..f427176ce2c34 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1474,6 +1474,7 @@ 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;
@@ -1490,8 +1491,7 @@ 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)) {
@@ -1500,11 +1500,9 @@ 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);
}
@@ -1520,12 +1518,16 @@ 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;
--
2.45.2