[PATCH v2 4/4] kvm: Enable dirty ring for arm64

[Gavin Shan]

arm64 has different capability from x86 to enable the dirty ring, which
is KVM_CAP_DIRTY_LOG_RING_ACQ_REL. Besides, arm64 also needs the backup
bitmap extension (KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP) when 'kvm-arm-gicv3'
or 'arm-its-kvm' device is enabled. Here the extension is always enabled
and the unnecessary overhead to do the last stage of dirty log synchronization
when those two devices aren't used is introduced, but the overhead should
be very small and acceptable. The benefit is cover future cases where those
two devices are used without modifying the code.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
---
 accel/kvm/kvm-all.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index e5035026c9..d96bca618b 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1457,6 +1457,7 @@ static int kvm_dirty_ring_init(KVMState *s)
 {
     uint32_t ring_size = s->kvm_dirty_ring_size;
     uint64_t ring_bytes = ring_size * sizeof(struct kvm_dirty_gfn);
+    unsigned int capability = KVM_CAP_DIRTY_LOG_RING;
     int ret;
 
     s->kvm_dirty_ring_size = 0;
@@ -1471,7 +1472,12 @@ static int kvm_dirty_ring_init(KVMState *s)
      * Read the max supported pages. Fall back to dirty logging mode
      * if the dirty ring isn't supported.
      */
-    ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
+    ret = kvm_vm_check_extension(s, capability);
+    if (ret <= 0) {
+        capability = KVM_CAP_DIRTY_LOG_RING_ACQ_REL;
+        ret = kvm_vm_check_extension(s, capability);
+    }
+
     if (ret <= 0) {
         warn_report("KVM dirty ring not available, using bitmap method");
         return 0;
@@ -1484,13 +1490,26 @@ static int kvm_dirty_ring_init(KVMState *s)
         return -EINVAL;
     }
 
-    ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, ring_bytes);
+    ret = kvm_vm_enable_cap(s, capability, 0, ring_bytes);
     if (ret) {
         error_report("Enabling of KVM dirty ring failed: %s. "
                      "Suggested minimum value is 1024.", strerror(-ret));
         return -EIO;
     }
 
+    /* Enable the backup bitmap if it is supported */
+    ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP);
+    if (ret > 0) {
+        ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP, 0);
+        if (ret) {
+            error_report("Enabling of KVM dirty ring's backup bitmap failed: "
+                         "%s. ", strerror(-ret));
+            return -EIO;
+        }
+
+        s->kvm_dirty_ring_with_bitmap = true;
+    }
+
     s->kvm_dirty_ring_size = ring_size;
     s->kvm_dirty_ring_bytes = ring_bytes;
 
-- 
2.23.0