The patch titled
Subject: mm/hugetlb: don't map folios writable without VM_WRITE when copying during fork()
has been added to the -mm mm-unstable branch. Its filename is
mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork.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/hugetlb: don't map folios writable without VM_WRITE when copying during fork()
Date: Wed, 4 Dec 2024 16:31:00 +0100
If we have to trigger a hugetlb folio copy during fork() because the anon
folio might be pinned, we currently unconditionally create a writable PTE.
However, the VMA might not have write permissions (VM_WRITE) at that
point.
Fix it by checking the VMA for VM_WRITE. Make the code less error prone
by moving checking for VM_WRITE into make_huge_pte(), and letting callers
only specify whether we should try making it writable.
A simple reproducer that longterm-pins the folios using liburing to then
mprotect(PROT_READ) the folios befor fork() [1] results in:
Before:
[FAIL] access should not have worked
After:
[PASS] access did not work as expected
[1] https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/hugetlb-mkwrite-fork.c
This is rather a corner case, so stable might not be warranted.
Link: https://lkml.kernel.org/r/20241204153100.1967364-1-david@xxxxxxxxxx
Fixes: 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Guillaume Morin <guillaume@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork
+++ a/mm/hugetlb.c
@@ -5155,12 +5155,12 @@ const struct vm_operations_struct hugetl
};
static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
- int writable)
+ bool try_mkwrite)
{
pte_t entry;
unsigned int shift = huge_page_shift(hstate_vma(vma));
- if (writable) {
+ if (try_mkwrite && (vma->vm_flags & VM_WRITE)) {
entry = huge_pte_mkwrite(huge_pte_mkdirty(mk_huge_pte(page,
vma->vm_page_prot)));
} else {
@@ -5220,7 +5220,7 @@ static void
hugetlb_install_folio(struct vm_area_struct *vma, pte_t *ptep, unsigned long addr,
struct folio *new_folio, pte_t old, unsigned long sz)
{
- pte_t newpte = make_huge_pte(vma, &new_folio->page, 1);
+ pte_t newpte = make_huge_pte(vma, &new_folio->page, true);
__folio_mark_uptodate(new_folio);
hugetlb_add_new_anon_rmap(new_folio, vma, addr);
@@ -6239,8 +6239,7 @@ static vm_fault_t hugetlb_no_page(struct
hugetlb_add_new_anon_rmap(folio, vma, vmf->address);
else
hugetlb_add_file_rmap(folio);
- new_pte = make_huge_pte(vma, &folio->page, ((vma->vm_flags & VM_WRITE)
- && (vma->vm_flags & VM_SHARED)));
+ new_pte = make_huge_pte(vma, &folio->page, vma->vm_flags & VM_SHARED);
/*
* If this pte was previously wr-protected, keep it wr-protected even
* if populated.
@@ -6572,7 +6571,6 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_
spinlock_t *ptl;
int ret = -ENOMEM;
struct folio *folio;
- int writable;
bool folio_in_pagecache = false;
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
@@ -6727,12 +6725,8 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_
* For either: (1) CONTINUE on a non-shared VMA, or (2) UFFDIO_COPY
* with wp flag set, don't set pte write bit.
*/
- if (wp_enabled || (is_continue && !vm_shared))
- writable = 0;
- else
- writable = dst_vma->vm_flags & VM_WRITE;
-
- _dst_pte = make_huge_pte(dst_vma, &folio->page, writable);
+ _dst_pte = make_huge_pte(dst_vma, &folio->page,
+ !wp_enabled && !(is_continue && !vm_shared));
/*
* Always mark UFFDIO_COPY page dirty; note that this may not be
* extremely important for hugetlbfs for now since swapping is not
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm.patch
mm-filemap-dont-call-folio_test_locked-without-a-reference-in-next_uptodate_folio.patch
docs-tmpfs-update-the-large-folios-policy-for-tmpfs-and-shmem.patch
mm-memory_hotplug-move-debug_pagealloc_map_pages-into-online_pages_range.patch
mm-page_isolation-dont-pass-gfp-flags-to-isolate_single_pageblock.patch
mm-page_isolation-dont-pass-gfp-flags-to-start_isolate_page_range.patch
mm-page_alloc-make-__alloc_contig_migrate_range-static.patch
mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch
mm-page_alloc-forward-the-gfp-flags-from-alloc_contig_range-to-post_alloc_hook.patch
powernv-memtrace-use-__gfp_zero-with-alloc_contig_pages.patch
mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork.patch
