On Fri, Aug 24, 2018 at 08:05:46PM -0400, Zi Yan wrote:
> 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.
You are right, Andrew do you want to repost or can you edit above if
to:
if (thp_migration_supported() && is_migration_entry(entry)) {
Cheers,
Jérôme
