On Fri, Dec 04, 2020 at 03:48:41PM +0530, Bharata B Rao wrote:
> On Thu, Dec 03, 2020 at 04:08:12PM +1100, Alistair Popple wrote:
> > migrate_vma_pages() may still clear MIGRATE_PFN_MIGRATE on pages which
> > are not able to be migrated. Drivers may safely copy data prior to
> > calling migrate_vma_pages() however a remote mapping must not be
> > established until after migrate_vma_pages() has returned as the
> > migration could still fail.
> >
> > UV_PAGE_IN_in both copies and maps the data page, therefore it should
> > only be called after checking the results of migrate_vma_pages().
> >
> > Signed-off-by: Alistair Popple <alist...@popple.id.au>
> > ---
> > arch/powerpc/kvm/book3s_hv_uvmem.c | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c
> > b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > index 84e5a2dc8be5..08aa6a90c525 100644
> > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > @@ -762,7 +762,10 @@ static int kvmppc_svm_page_in(struct vm_area_struct
> > *vma,
> > goto out_finalize;
> > }
> >
> > - if (pagein) {
> > + *mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
> > + migrate_vma_pages(&mig);
> > +
> > + if ((*mig.src & MIGRATE_PFN_MIGRATE) && pagein) {
> > pfn = *mig.src >> MIGRATE_PFN_SHIFT;
> > spage = migrate_pfn_to_page(*mig.src);
> > if (spage) {
> > @@ -773,8 +776,6 @@ static int kvmppc_svm_page_in(struct vm_area_struct
> > *vma,
> > }
> > }
> >
> > - *mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
> > - migrate_vma_pages(&mig);
> > out_finalize:
> > migrate_vma_finalize(&mig);
> > return ret;
This patch certainly looks like the problem, that has been hurting
us for a while. Let me run this patch through my SVM tests. Looks very
promising.
BTW: The code does a similar thing while paging out. It pages out from the
UV, and then does the migration. Is there a bug there aswell?
RP
