[3.5.y.z extended stable] Patch "KVM: IOMMU: hva align mapping page size" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    KVM: IOMMU: hva align mapping page size

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f402fa19d9039c955c168aa34fd7c201af4e563e Mon Sep 17 00:00:00 2001
From: Greg Edwards <gedwards at ddn.com>
Date: Mon, 4 Nov 2013 09:08:12 -0700
Subject: KVM: IOMMU: hva align mapping page size

commit 27ef63c7e97d1e5dddd85051c03f8d44cc887f34 upstream.

When determining the page size we could use to map with the IOMMU, the
page size should also be aligned with the hva, not just 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.

Ensure the IOMMU mapping page size is aligned with the hva corresponding
to the gfn, which does reflect the alignment within the hugetlbfs file.

Reviewed-by: Marcelo Tosatti <mtosatti at redhat.com>
Signed-off-by: Greg Edwards <gedwards at ddn.com>
Signed-off-by: Gleb Natapov <gleb at redhat.com>
[ luis: backported to 3.5:
  - replaced __gfn_to_hva_memslot by gfn_to_hva_memslot ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 virt/kvm/iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index e9fff98..53d34f6 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -101,6 +101,10 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
 		while ((gfn << PAGE_SHIFT) & (page_size - 1))
 			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;
+
 		/*
 		 * Pin all pages we are about to map in memory. This is
 		 * important because we unmap and unpin in 4kb steps later.
--
1.8.3.2