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Subject[PATCH] userfaultfd: hugetlbfs: Fix userfaultfd_huge_must_wait pte access
Date
Use huge_ptep_get to translate huge ptes to normal ptes so we can
check them with the huge_pte_* functions. Otherwise some architectures
will check the wrong values and will not wait for userspace to bring
in the memory.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges")
---
fs/userfaultfd.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 123bf7d516fc..594d192b2331 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -222,24 +222,26 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
unsigned long reason)
{
struct mm_struct *mm = ctx->mm;
- pte_t *pte;
+ pte_t *ptep, pte;
bool ret = true;

VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));

- pte = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
- if (!pte)
+ ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
+
+ if (!ptep)
goto out;

ret = false;
+ pte = huge_ptep_get(ptep);

/*
* Lockless access: we're in a wait_event so it's ok if it
* changes under us.
*/
- if (huge_pte_none(*pte))
+ if (huge_pte_none(pte))
ret = true;
- if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP))
+ if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
ret = true;
out:
return ret;
--
2.14.3
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