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mm/hugetlb: stop using avoid_reserve flag in fork()

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When fork() and stumble on top of a dma-pinned hugetlb private page, CoW
must happen during fork() to guarantee dma coherency.

In this specific path, hugetlb pages need to be allocated for the child
process.  Stop using avoid_reserve=1 flag here: it's not required to be
used here, as dest_vma (which is destined to be a MAP_PRIVATE hugetlb vma)
will have no private vma resv map, and that will make sure it won't be
able to use a vma reservation later.

No functional change intended with this change.  Said that, it's still
wanted to do this, so as to reduce the usage of avoid_reserve to the only
one user, which is also why this flag was introduced initially in commit
04f2cbe356 ("hugetlb: guarantee that COW faults for a process that
called mmap(MAP_PRIVATE) on hugetlbfs will succeed").  I don't see whoever
else should set it at all.

Further patch will clean up resv accounting based on this.

Link: https://lkml.kernel.org/r/20250107204002.2683356-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Xu 2025-01-07 15:39:57 -05:00 committed by Andrew Morton
parent 58db7c5fbe
commit be8d7314b1
1 changed files with 1 additions and 1 deletions
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2
mm/hugetlb.c
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@ -5373,7 +5373,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
spin_unlock(src_ptl);
spin_unlock(dst_ptl);
/* Do not use reserve as it's private owned */
new_folio = alloc_hugetlb_folio(dst_vma, addr, 1);
new_folio = alloc_hugetlb_folio(dst_vma, addr, 0);
if (IS_ERR(new_folio)) {
folio_put(pte_folio);
ret = PTR_ERR(new_folio);