Re: [PATCH 4/7] mm/hmm: properly handle migration pmd
From: Zi Yan <hidden>
Date: 2018-08-25 00:05:53
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Hi Jérôme, On 24 Aug 2018, at 15:25, jglisse@redhat.com wrote:
quoted hunk ↗ jump to hunk
From: Jérôme Glisse <redacted> Before this patch migration pmd entry (!pmd_present()) would have been treated as a bad entry (pmd_bad() returns true on migration pmd entry). The outcome was that device driver would believe that the range covered by the pmd was bad and would either SIGBUS or simply kill all the device's threads (each device driver decide how to react when the device tries to access poisonnous or invalid range of memory). This patch explicitly handle the case of migration pmd entry which are non present pmd entry and either wait for the migration to finish or report empty range (when device is just trying to pre- fill a range of virtual address and thus do not want to wait or trigger page fault). Signed-off-by: Aneesh Kumar K.V <redacted> Signed-off-by: Jérôme Glisse <redacted> Cc: Ralph Campbell <redacted> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Andrew Morton <akpm@linux-foundation.org> --- mm/hmm.c | 45 +++++++++++++++++++++++++++++++++++++++------ 1 file changed, 39 insertions(+), 6 deletions(-)diff --git a/mm/hmm.c b/mm/hmm.c index a16678d08127..659efc9aada6 100644 --- a/mm/hmm.c +++ b/mm/hmm.c@@ -577,22 +577,47 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, { struct hmm_vma_walk *hmm_vma_walk = walk->private; struct hmm_range *range = hmm_vma_walk->range; + struct vm_area_struct *vma = walk->vma; uint64_t *pfns = range->pfns; unsigned long addr = start, i; pte_t *ptep; + pmd_t pmd; - i = (addr - range->start) >> PAGE_SHIFT; again: - if (pmd_none(*pmdp)) + pmd = READ_ONCE(*pmdp); + if (pmd_none(pmd)) return hmm_vma_walk_hole(start, end, walk); - if (pmd_huge(*pmdp) && (range->vma->vm_flags & VM_HUGETLB)) + if (pmd_huge(pmd) && (range->vma->vm_flags & VM_HUGETLB)) return hmm_pfns_bad(start, end, walk); - if (pmd_devmap(*pmdp) || pmd_trans_huge(*pmdp)) { - pmd_t pmd; + if (!pmd_present(pmd)) { + swp_entry_t entry = pmd_to_swp_entry(pmd); + + if (is_migration_entry(entry)) {
I think you should check thp_migration_supported() here, since PMD migration is only enabled in x86_64 systems. Other architectures should treat PMD migration entries as bad.
+ bool fault, write_fault;
+ unsigned long npages;
+ uint64_t *pfns;
+
+ i = (addr - range->start) >> PAGE_SHIFT;
+ npages = (end - addr) >> PAGE_SHIFT;
+ pfns = &range->pfns[i];
+
+ hmm_range_need_fault(hmm_vma_walk, pfns, npages,
+ 0, &fault, &write_fault);
+ if (fault || write_fault) {
+ hmm_vma_walk->last = addr;
+ pmd_migration_entry_wait(vma->vm_mm, pmdp);
+ return -EAGAIN;
+ }
+ return 0;
+ }
+
+ return hmm_pfns_bad(start, end, walk);
+ }— Best Regards, Yan Zi
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