[PATCH 1/2] [RFC] proc: pagemap: Expose whether a PTE is writable

Richard Weinberger
2024-03-06T23:24:07Z

Is a PTE present and writable, bit 58 will be set.
This allows detecting CoW memory mappings and other mappings
where a write access will cause a page fault.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
fs/proc/task_mmu.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3f78ebbb795f..7c7e0e954c02 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1341,6 +1341,7 @@ struct pagemapread {
#define PM_SOFT_DIRTY BIT_ULL(55)
#define PM_MMAP_EXCLUSIVE BIT_ULL(56)
#define PM_UFFD_WP BIT_ULL(57)
+#define PM_WRITE BIT_ULL(58)
#define PM_FILE BIT_ULL(61)
#define PM_SWAP BIT_ULL(62)
#define PM_PRESENT BIT_ULL(63)
@@ -1417,6 +1418,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
flags |= PM_SOFT_DIRTY;
if (pte_uffd_wp(pte))
flags |= PM_UFFD_WP;
+ if (pte_write(pte))
+ flags |= PM_WRITE;
} else if (is_swap_pte(pte)) {
swp_entry_t entry;
if (pte_swp_soft_dirty(pte))
@@ -1483,6 +1486,8 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
flags |= PM_SOFT_DIRTY;
if (pmd_uffd_wp(pmd))
flags |= PM_UFFD_WP;
+ if (pmd_write(pmd))
+ flags |= PM_WRITE;
if (pm->show_pfn)
frame = pmd_pfn(pmd) +
((addr & ~PMD_MASK) >> PAGE_SHIFT);
@@ -1586,6 +1591,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask,
if (huge_pte_uffd_wp(pte))
flags |= PM_UFFD_WP;

+ if (pte_write(pte))
+ flags |= PM_WRITE;
+
flags |= PM_PRESENT;
if (pm->show_pfn)
frame = pte_pfn(pte) +
--
2.35.3