diff mbox series

[PULL,10/39] KVM: dirty ring: add missing memory barrier

Message ID 20220901182429.93533-11-pbonzini@redhat.com
State New
Headers show
Series [PULL,01/39] esp: Handle CMD_BUSRESET by resetting the SCSI bus | expand

Commit Message

Paolo Bonzini Sept. 1, 2022, 6:24 p.m. UTC 
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 <gshan@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 accel/kvm/kvm-all.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
diff mbox series

Patch

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)