KVM: Enable snooping control for supported hardware
Memory aliases with different memory type is a problem for guest. For the guest
without assigned device, the memory type of guest memory would always been the
same as host(WB); but for the assigned device, some part of memory may be used
as DMA and then set to uncacheable memory type(UC/WC), which would be a conflict of
host memory type then be a potential issue.
Snooping control can guarantee the cache correctness of memory go through the
DMA engine of VT-d.
[avi: fix build on ia64]
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8a6f6b6..253d8f6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -393,6 +393,7 @@
struct list_head active_mmu_pages;
struct list_head assigned_dev_head;
struct iommu_domain *iommu_domain;
+ int iommu_flags;
struct kvm_pic *vpic;
struct kvm_ioapic *vioapic;
struct kvm_pit *vpit;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 59b080c..e8a5649 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3581,11 +3581,26 @@
{
u64 ret;
+ /* For VT-d and EPT combination
+ * 1. MMIO: always map as UC
+ * 2. EPT with VT-d:
+ * a. VT-d without snooping control feature: can't guarantee the
+ * result, try to trust guest.
+ * b. VT-d with snooping control feature: snooping control feature of
+ * VT-d engine can guarantee the cache correctness. Just set it
+ * to WB to keep consistent with host. So the same as item 3.
+ * 3. EPT without VT-d: always map as WB and set IGMT=1 to keep
+ * consistent with host MTRR
+ */
if (is_mmio)
ret = MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT;
+ else if (vcpu->kvm->arch.iommu_domain &&
+ !(vcpu->kvm->arch.iommu_flags & KVM_IOMMU_CACHE_COHERENCY))
+ ret = kvm_get_guest_memory_type(vcpu, gfn) <<
+ VMX_EPT_MT_EPTE_SHIFT;
else
- ret = (kvm_get_guest_memory_type(vcpu, gfn) <<
- VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IGMT_BIT;
+ ret = (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT)
+ | VMX_EPT_IGMT_BIT;
return ret;
}