[v2.6.34-stable 008/213] KVM: lock slots_lock around device assignment

From: Paul Gortmaker
Date: Wed Feb 05 2014 - 16:17:58 EST

From: Alex Williamson <alex.williamson@xxxxxxxxxx>

This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.

commit 21a1416a1c945c5aeaeaf791b63c64926018eb77 upstream.

As pointed out by Jason Baron, when assigning a device to a guest
we first set the iommu domain pointer, which enables mapping
and unmapping of memory slots to the iommu. This leaves a window
where this path is enabled, but we haven't synchronized the iommu
mappings to the existing memory slots. Thus a slot being removed
at that point could send us down unexpected code paths removing
non-existent pinnings and iommu mappings. Take the slots_lock
around creating the iommu domain and initial mappings as well as
around iommu teardown to avoid this race.

Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
[PG: drop goto for EPERM check, 2.6.34 doesn't have that code]
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
virt/kvm/iommu.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index ac765f648218..8c510edca9c9 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -174,18 +174,20 @@ int kvm_iommu_map_guest(struct kvm *kvm)
return -ENODEV;

+ mutex_lock(&kvm->slots_lock);
kvm->arch.iommu_domain = iommu_domain_alloc();
- if (!kvm->arch.iommu_domain)
- return -ENOMEM;
+ if (!kvm->arch.iommu_domain) {
+ r = -ENOMEM;
+ goto out_unlock;
+ }

r = kvm_iommu_map_memslots(kvm);
if (r)
- goto out_unmap;
- return 0;
+ kvm_iommu_unmap_memslots(kvm);

- kvm_iommu_unmap_memslots(kvm);
+ mutex_unlock(&kvm->slots_lock);
return r;

@@ -239,7 +241,11 @@ int kvm_iommu_unmap_guest(struct kvm *kvm)
if (!domain)
return 0;

+ mutex_lock(&kvm->slots_lock);
+ kvm->arch.iommu_domain = NULL;
+ mutex_unlock(&kvm->slots_lock);
return 0;

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