[PATCH] powerpc/book3s_hv_uvmem: Check for failed page migration

[Alistair Popple]

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;
-- 
2.20.1