From 4802bf910eee98312c4a9777ac2567e6a0445c46 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 26 Aug 2022 13:00:00 +0200 Subject: [PATCH] KVM: dirty ring: add missing memory barrier MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Gavin Shan Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Peter Xu Signed-off-by: Paolo Bonzini --- 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)