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.
Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/vmx.c | 19 +++++++++++++++++--
virt/kvm/iommu.c | 27 ++++++++++++++++++++++++---
3 files changed, 43 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b6d01a4..b972889 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -395,6 +395,8 @@ struct kvm_arch{
struct list_head active_mmu_pages;
struct list_head assigned_dev_head;
struct iommu_domain *iommu_domain;
+#define KVM_IOMMU_CACHE_COHERENCY 0x1
+ 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 7c4f5a3..79fc401 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3682,11 +3682,26 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
{
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;
}
diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index 4c40375..1514758 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -39,11 +39,16 @@ int kvm_iommu_map_pages(struct kvm *kvm,
pfn_t pfn;
int i, r = 0;
struct iommu_domain *domain = kvm->arch.iommu_domain;
+ int flags;
/* check if iommu exists and in use */
if (!domain)
return 0;
+ flags = IOMMU_READ | IOMMU_WRITE;
+ if (kvm->arch.iommu_flags & KVM_IOMMU_CACHE_COHERENCY)
+ flags |= IOMMU_CACHE;
+
for (i = 0; i < npages; i++) {
/* check if already mapped */
if (iommu_iova_to_phys(domain, gfn_to_gpa(gfn)))
@@ -53,8 +58,7 @@ int kvm_iommu_map_pages(struct kvm *kvm,
r = iommu_map_range(domain,
gfn_to_gpa(gfn),
pfn_to_hpa(pfn),
- PAGE_SIZE,
- IOMMU_READ | IOMMU_WRITE);
+ PAGE_SIZE, flags);
if (r) {
printk(KERN_ERR "kvm_iommu_map_address:"
"iommu failed to map pfn=%lx\n", pfn);
@@ -88,7 +92,7 @@ int kvm_assign_device(struct kvm *kvm,
{
struct pci_dev *pdev = NULL;
struct iommu_domain *domain = kvm->arch.iommu_domain;
- int r;
+ int r, last_flags;
/* check if iommu exists and in use */
if (!domain)
@@ -107,12 +111,29 @@ int kvm_assign_device(struct kvm *kvm,
return r;
}
+ last_flags = kvm->arch.iommu_flags;
+ if (iommu_domain_has_cap(kvm->arch.iommu_domain,
+ IOMMU_CAP_CACHE_COHERENCY))
+ kvm->arch.iommu_flags |= KVM_IOMMU_CACHE_COHERENCY;
+
+ /* Check if need to update IOMMU page table for guest memory */
+ if ((last_flags ^ kvm->arch.iommu_flags) ==
+ KVM_IOMMU_CACHE_COHERENCY) {
+ kvm_iommu_unmap_memslots(kvm);
+ r = kvm_iommu_map_memslots(kvm);
+ if (r)
+ goto out_unmap;
+ }
+
printk(KERN_DEBUG "assign device: host bdf = %x:%x:%x\n",
assigned_dev->host_busnr,
PCI_SLOT(assigned_dev->host_devfn),
PCI_FUNC(assigned_dev->host_devfn));
return 0;
+out_unmap:
+ kvm_iommu_unmap_memslots(kvm);
+ return r;
}
int kvm_deassign_device(struct kvm *kvm,
--
1.5.4.5
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