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KVM: dirty ring: add missing memory barrier

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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>
This commit is contained in:
Paolo Bonzini 2022-08-26 13:00:00 +02:00
parent e3af71e900
commit 4802bf910e
1 changed files with 5 additions and 1 deletions
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6
accel/kvm/kvm-all.c
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@ -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)