Messages in this thread | | | Date | Wed, 7 Dec 2022 12:34:34 -0800 | Subject | Re: [PATCH v2 08/10] mm/hugetlb: Make walk_hugetlb_range() safe to pmd unshare | From | John Hubbard <> |
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On 12/7/22 12:30, Peter Xu wrote: > Since walk_hugetlb_range() walks the pgtable, it needs the vma lock > to make sure the pgtable page will not be freed concurrently. > > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > arch/s390/mm/gmap.c | 2 ++ > fs/proc/task_mmu.c | 2 ++ > include/linux/pagewalk.h | 11 ++++++++++- > mm/hmm.c | 15 ++++++++++++++- > mm/pagewalk.c | 2 ++ > 5 files changed, 30 insertions(+), 2 deletions(-)
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks, -- John Hubbard NVIDIA
> > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > index 8947451ae021..292a54c490d4 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -2643,7 +2643,9 @@ static int __s390_enable_skey_hugetlb(pte_t *pte, unsigned long addr, > end = start + HPAGE_SIZE - 1; > __storage_key_init_range(start, end); > set_bit(PG_arch_1, &page->flags); > + hugetlb_vma_unlock_read(walk->vma); > cond_resched(); > + hugetlb_vma_lock_read(walk->vma); > return 0; > } > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index e35a0398db63..cf3887fb2905 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1613,7 +1613,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask, > frame++; > } > > + hugetlb_vma_unlock_read(walk->vma); > cond_resched(); > + hugetlb_vma_lock_read(walk->vma); > > return err; > } > diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h > index 959f52e5867d..27a6df448ee5 100644 > --- a/include/linux/pagewalk.h > +++ b/include/linux/pagewalk.h > @@ -21,7 +21,16 @@ struct mm_walk; > * depth is -1 if not known, 0:PGD, 1:P4D, 2:PUD, 3:PMD. > * Any folded depths (where PTRS_PER_P?D is equal to 1) > * are skipped. > - * @hugetlb_entry: if set, called for each hugetlb entry > + * @hugetlb_entry: if set, called for each hugetlb entry. This hook > + * function is called with the vma lock held, in order to > + * protect against a concurrent freeing of the pte_t* or > + * the ptl. In some cases, the hook function needs to drop > + * and retake the vma lock in order to avoid deadlocks > + * while calling other functions. In such cases the hook > + * function must either refrain from accessing the pte or > + * ptl after dropping the vma lock, or else revalidate > + * those items after re-acquiring the vma lock and before > + * accessing them. > * @test_walk: caller specific callback function to determine whether > * we walk over the current vma or not. Returning 0 means > * "do page table walk over the current vma", returning > diff --git a/mm/hmm.c b/mm/hmm.c > index 3850fb625dda..796de6866089 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -493,8 +493,21 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask, > required_fault = > hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags); > if (required_fault) { > + int ret; > + > spin_unlock(ptl); > - return hmm_vma_fault(addr, end, required_fault, walk); > + hugetlb_vma_unlock_read(vma); > + /* > + * Avoid deadlock: drop the vma lock before calling > + * hmm_vma_fault(), which will itself potentially take and > + * drop the vma lock. This is also correct from a > + * protection point of view, because there is no further > + * use here of either pte or ptl after dropping the vma > + * lock. > + */ > + ret = hmm_vma_fault(addr, end, required_fault, walk); > + hugetlb_vma_lock_read(vma); > + return ret; > } > > pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT); > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index 7f1c9b274906..d98564a7be57 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -302,6 +302,7 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end, > const struct mm_walk_ops *ops = walk->ops; > int err = 0; > > + hugetlb_vma_lock_read(vma); > do { > next = hugetlb_entry_end(h, addr, end); > pte = huge_pte_offset(walk->mm, addr & hmask, sz); > @@ -314,6 +315,7 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end, > if (err) > break; > } while (addr = next, addr != end); > + hugetlb_vma_unlock_read(vma); > > return err; > }
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