kvm/vfio: Support for DMA coherent IOMMUs

VFIO now has support for using the IOMMU_CACHE flag and a mechanism
for an external user to test the current operating mode of the IOMMU.
Add support for this to the kvm-vfio pseudo device so that we only
register noncoherent DMA when necessary.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 20 insertions, 7 deletions

diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index b4f9507ae650..ba1a93f935c7 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -59,6 +59,22 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
         symbol_put(vfio_group_put_external_user);
 }
 
+static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
+{
+        long (*fn)(struct vfio_group *, unsigned long);
+        long ret;
+
+        fn = symbol_get(vfio_external_check_extension);
+        if (!fn)
+                return false;
+
+        ret = fn(vfio_group, VFIO_DMA_CC_IOMMU);
+
+        symbol_put(vfio_external_check_extension);
+
+        return ret > 0;
+}
+
 /*
  * Groups can use the same or different IOMMU domains.  If the same then
  * adding a new group may change the coherency of groups we've previously
@@ -75,13 +91,10 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
         mutex_lock(&kv->lock);
 
         list_for_each_entry(kvg, &kv->group_list, node) {
-                /*
-                 * TODO: We need an interface to check the coherency of
-                 * the IOMMU domain this group is using.  For now, assume
-                 * it's always noncoherent.
-                 */
-                noncoherent = true;
-                break;
+                if (!kvm_vfio_group_is_coherent(kvg->vfio_group)) {
+                        noncoherent = true;
+                        break;
+                }
         }
 
         if (noncoherent != kv->noncoherent) {