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

[Paul Gortmaker]

From: Alex Williamson <alex.williamson@xxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    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);
 
-out_unmap:
-	kvm_iommu_unmap_memslots(kvm);
+out_unlock:
+	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_iommu_unmap_memslots(kvm);
+	kvm->arch.iommu_domain = NULL;
+	mutex_unlock(&kvm->slots_lock);
+
 	iommu_domain_free(domain);
 	return 0;
 }
-- 
1.8.5.2

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