[PATCH] KVM: dirty ring: Add memory barrier when marking pfn collected

[Peter Xu]

Following commit 4802bf910eee9, add the other missing barrier when marking
the PFN as collected.  This will also be required just like 4802bf910eee9
on weak ordering architectures like aarch64.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@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 136c8eaed3..60a044048e 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -728,7 +728,11 @@ static bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
 
 static void dirty_gfn_set_collected(struct kvm_dirty_gfn *gfn)
 {
-    gfn->flags = KVM_DIRTY_GFN_F_RESET;
+    /*
+     * Write the flags after reading the entry.  Should pair with another
+     * smp_load_acquire() in KVM when reset dirty rings.
+     */
+    qatomic_store_release(&gfn->flags, KVM_DIRTY_GFN_F_RESET);
 }
 
 /*
-- 
2.32.0