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From: Richard Weinberger <richard@nod.at>
To: linux-mm@kvack.org
Cc: linux-fsdevel@vger.kernel.org,
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	linux-doc@vger.kernel.org,
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	Richard Weinberger <richard@nod.at>
Subject: [PATCH 1/2] [RFC] proc: pagemap: Expose whether a PTE is writable
Date: Thu,  7 Mar 2024 00:23:38 +0100
Message-Id: <20240306232339.29659-1-richard@nod.at>
Precedence: bulk
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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 |=3D PM_SOFT_DIRTY;
 		if (pte_uffd_wp(pte))
 			flags |=3D PM_UFFD_WP;
+		if (pte_write(pte))
+			flags |=3D 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 |=3D PM_SOFT_DIRTY;
 			if (pmd_uffd_wp(pmd))
 				flags |=3D PM_UFFD_WP;
+			if (pmd_write(pmd))
+				flags |=3D PM_WRITE;
 			if (pm->show_pfn)
 				frame =3D pmd_pfn(pmd) +
 					((addr & ~PMD_MASK) >> PAGE_SHIFT);
@@ -1586,6 +1591,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsig=
ned long hmask,
 		if (huge_pte_uffd_wp(pte))
 			flags |=3D PM_UFFD_WP;
=20
+		if (pte_write(pte))
+			flags |=3D PM_WRITE;
+
 		flags |=3D PM_PRESENT;
 		if (pm->show_pfn)
 			frame =3D pte_pfn(pte) +
--=20
2.35.3