On Fri, Nov 01, 2013 at 10:08:55AM -0600, Greg Edwards wrote: > When determining the page size we could use to map with the IOMMU, the > page size should be aligned with the hva, not the gfn. The gfn may not > reflect the real alignment within the hugetlbfs file. > > Most of the time, this works fine. However, if the hugetlbfs file is > backed by non-contiguous huge pages, a multi-huge page memslot starts at > an unaligned offset within the hugetlbfs file, and the gfn is aligned > with respect to the huge page size, kvm_host_page_size() will return the > huge page size and we will use that to map with the IOMMU. > > When we later unpin that same memslot, the IOMMU returns the unmap size > as the huge page size, and we happily unpin that many pfns in > monotonically increasing order, not realizing we are spanning > non-contiguous huge pages and partially unpin the wrong huge page. > > Instead, ensure the IOMMU mapping page size is aligned with the hva > corresponding to the gfn, which does reflect the alignment within the > hugetlbfs file. > > Signed-off-by: Greg Edwards <gedwards@xxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > This resolves the bug previously reported (and misdiagnosed) here: > > http://www.spinics.net/lists/kvm/msg97599.html > > virt/kvm/iommu.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c > index 72a130b..0e2ff32 100644 > --- a/virt/kvm/iommu.c > +++ b/virt/kvm/iommu.c > @@ -99,8 +99,8 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot) > while ((gfn + (page_size >> PAGE_SHIFT)) > end_gfn) > page_size >>= 1; > > - /* Make sure gfn is aligned to the page size we want to map */ > - while ((gfn << PAGE_SHIFT) & (page_size - 1)) > + /* Make sure hva is aligned to the page size we want to map */ > + while (__gfn_to_hva_memslot(slot, gfn) & (page_size - 1)) > page_size >>= 1; gfn should be aligned to page size as well (IOMMU requirement), so don't drop that check. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
