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>

1 files changed, 24 insertions, 3 deletions

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index 4c4037503600..15147583abd1 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,