Hi Jérôme,
On 24 Aug 2018, at 15:25, jglisse@xxxxxxxxxx wrote:
> From: Jérôme Glisse <jglisse@xxxxxxxxxx>
>
> 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 <aneesh.kumar@xxxxxxxxxxxxx>
> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 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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