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

[Gavin Shan <gshan@redhat.com>]

On 9/23/22 7:35 AM, Peter Xu wrote:
> 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(-)
> 

Reviewed-by: Gavin Shan <gshan@redhat.com>

> 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);
>   }
>   
>   /*
>