The patch titled
Subject: mm/memory: ignore writable bit in folio_pte_batch()
has been added to the -mm mm-unstable branch. Its filename is
mm-memory-ignore-writable-bit-in-folio_pte_batch.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-ignore-writable-bit-in-folio_pte_batch.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/memory: ignore writable bit in folio_pte_batch()
Date: Mon, 22 Jan 2024 20:42:00 +0100
.. and conditionally return to the caller if any pte except the first
one is writable. fork() has to make sure to properly write-protect in
case any PTE is writable. Other users (e.g., page unmaping) won't care.
Link: https://lkml.kernel.org/r/20240122194200.381241-12-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
Cc: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Dinh Nguyen <dinguyen@xxxxxxxxxx>
Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
--- a/mm/memory.c~mm-memory-ignore-writable-bit-in-folio_pte_batch
+++ a/mm/memory.c
@@ -955,7 +955,7 @@ static __always_inline void __copy_prese
static inline pte_t __pte_batch_clear_ignored(pte_t pte)
{
- return pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte)));
+ return pte_wrprotect(pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte))));
}
/*
@@ -963,20 +963,29 @@ static inline pte_t __pte_batch_clear_ig
* pages of the same folio.
*
* All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN.
- * the accessed bit, dirty bit and soft-dirty bit.
+ * the accessed bit, dirty bit, soft-dirty bit and writable bit.
+ . If "any_writable" is set, it will indicate if any other PTE besides the
+ * first (given) PTE is writable.
*/
static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
- pte_t *start_ptep, pte_t pte, int max_nr)
+ pte_t *start_ptep, pte_t pte, int max_nr, bool *any_writable)
{
unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio);
const pte_t *end_ptep = start_ptep + max_nr;
pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte));
pte_t *ptep = start_ptep + 1;
+ bool writable;
+
+ if (any_writable)
+ *any_writable = false;
VM_WARN_ON_FOLIO(!pte_present(pte), folio);
while (ptep != end_ptep) {
- pte = __pte_batch_clear_ignored(ptep_get(ptep));
+ pte = ptep_get(ptep);
+ if (any_writable)
+ writable = !!pte_write(pte);
+ pte = __pte_batch_clear_ignored(pte);
if (!pte_same(pte, expected_pte))
break;
@@ -989,6 +998,9 @@ static inline int folio_pte_batch(struct
if (pte_pfn(pte) == folio_end_pfn)
break;
+ if (any_writable)
+ *any_writable |= writable;
+
expected_pte = pte_next_pfn(expected_pte);
ptep++;
}
@@ -1010,6 +1022,7 @@ copy_present_ptes(struct vm_area_struct
{
struct page *page;
struct folio *folio;
+ bool any_writable;
int err, nr;
page = vm_normal_page(src_vma, addr, pte);
@@ -1024,7 +1037,8 @@ copy_present_ptes(struct vm_area_struct
* by keeping the batching logic separate.
*/
if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) {
- nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr);
+ nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr,
+ &any_writable);
if (folio_test_anon(folio)) {
folio_ref_add(folio, nr);
if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page,
@@ -1039,6 +1053,8 @@ copy_present_ptes(struct vm_area_struct
folio_dup_file_rmap_ptes(folio, page, nr);
rss[mm_counter_file(page)] += nr;
}
+ if (any_writable)
+ pte = pte_mkwrite(pte, src_vma);
__copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte,
addr, nr);
return nr;
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
uprobes-use-pagesize-aligned-virtual-address-when-replacing-pages.patch
arm-pgtable-define-pfn_pte_shift-on-arm-and-arm64.patch
nios2-pgtable-define-pfn_pte_shift.patch
powerpc-pgtable-define-pfn_pte_shift.patch
risc-pgtable-define-pfn_pte_shift.patch
s390-pgtable-define-pfn_pte_shift.patch
sparc-pgtable-define-pfn_pte_shift.patch
mm-memory-factor-out-copying-the-actual-pte-in-copy_present_pte.patch
mm-memory-pass-pte-to-copy_present_pte.patch
mm-memory-optimize-fork-with-pte-mapped-thp.patch
mm-memory-ignore-dirty-accessed-soft-dirty-bits-in-folio_pte_batch.patch
mm-memory-ignore-writable-bit-in-folio_pte_batch.patch
