The KVM_DIRTY_GFN_F_DIRTY flag ensures that the entry is valid. If
the read of the fields are not ordered after the read of the flag,
QEMU might see stale values.
Cc: Peter Xu <peterx@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
accel/kvm/kvm-all.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 8d81ab74de..136c8eaed3 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -719,7 +719,11 @@ static void kvm_dirty_ring_mark_page(KVMState *s, uint32_t
as_id,
static bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
{
- return gfn->flags == KVM_DIRTY_GFN_F_DIRTY;
+ /*
+ * Read the flags before the value. Pairs with barrier in
+ * KVM's kvm_dirty_ring_push() function.
+ */
+ return qatomic_load_acquire(&gfn->flags) == KVM_DIRTY_GFN_F_DIRTY;
}
static void dirty_gfn_set_collected(struct kvm_dirty_gfn *gfn)