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KVM: lock slots_lock around device assignment

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@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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1 parent 2225fd5 commit 21a1416a1c945c5aeaeaf791b63c64926018eb77 @awilliam awilliam committed with Marcelo Tosatti Apr 18, 2012
Showing with 15 additions and 8 deletions.
  1. +15 −8 virt/kvm/iommu.c
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23 virt/kvm/iommu.c
@@ -240,9 +240,13 @@ int kvm_iommu_map_guest(struct kvm *kvm)
return -ENODEV;
}
+ mutex_lock(&kvm->slots_lock);
+
kvm->arch.iommu_domain = iommu_domain_alloc(&pci_bus_type);
- if (!kvm->arch.iommu_domain)
- return -ENOMEM;
+ if (!kvm->arch.iommu_domain) {
+ r = -ENOMEM;
+ goto out_unlock;
+ }
if (!allow_unsafe_assigned_interrupts &&
!iommu_domain_has_cap(kvm->arch.iommu_domain,
@@ -253,17 +257,16 @@ int kvm_iommu_map_guest(struct kvm *kvm)
" module option.\n", __func__);
iommu_domain_free(kvm->arch.iommu_domain);
kvm->arch.iommu_domain = NULL;
- return -EPERM;
+ r = -EPERM;
+ 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;
}
@@ -340,7 +343,11 @@ 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;
}

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