On 26.06.2018 19:00, Mike Kravetz wrote: > On 06/26/2018 06:24 AM, Janosch Frank wrote: >> 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 <[email protected]> >> Fixes: 369cd2121be4 ("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for >> hugepmd ranges") > Adding linux-mm and Andrew on Cc: > > Thanks for catching and fixing this.
Sure I'd be happy if we get less of these problems with time, this one was rather painful to debug. :) > I think this needs to be fixed in stable as well. Correct? Assuming > userfaultfd is/can be enabled for impacted architectures. Correct, it seems I forgot the CC stable... > > Reviewed-by: Mike Kravetz <[email protected]> Thanks > -- Mike Kravetz >> --- >> 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; >>
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