* [PATCH v2] KVM: dirty ring: add missing memory barrier
@ 2022-08-27 8:22 Paolo Bonzini
2022-08-30 12:07 ` Philippe Mathieu-Daudé via
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Paolo Bonzini @ 2022-08-27 8:22 UTC (permalink / raw)
To: qemu-devel; +Cc: f4bug, Peter Xu, Gavin Shan
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: Peter Xu <peterx@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@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 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)
--
2.37.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2] KVM: dirty ring: add missing memory barrier
2022-08-27 8:22 [PATCH v2] KVM: dirty ring: add missing memory barrier Paolo Bonzini
@ 2022-08-30 12:07 ` Philippe Mathieu-Daudé via
2022-08-30 14:24 ` Peter Xu
2022-09-07 0:37 ` Gavin Shan
2 siblings, 0 replies; 4+ messages in thread
From: Philippe Mathieu-Daudé via @ 2022-08-30 12:07 UTC (permalink / raw)
To: Paolo Bonzini, qemu-devel; +Cc: Peter Xu, Gavin Shan
On 27/8/22 10:22, Paolo Bonzini wrote:
> 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: Peter Xu <peterx@redhat.com>
> Cc: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@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 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)
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] KVM: dirty ring: add missing memory barrier
2022-08-27 8:22 [PATCH v2] KVM: dirty ring: add missing memory barrier Paolo Bonzini
2022-08-30 12:07 ` Philippe Mathieu-Daudé via
@ 2022-08-30 14:24 ` Peter Xu
2022-09-07 0:37 ` Gavin Shan
2 siblings, 0 replies; 4+ messages in thread
From: Peter Xu @ 2022-08-30 14:24 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: qemu-devel, f4bug, Gavin Shan
On Sat, Aug 27, 2022 at 10:22:18AM +0200, Paolo Bonzini wrote:
> 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: Peter Xu <peterx@redhat.com>
> Cc: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Thanks!
--
Peter Xu
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] KVM: dirty ring: add missing memory barrier
2022-08-27 8:22 [PATCH v2] KVM: dirty ring: add missing memory barrier Paolo Bonzini
2022-08-30 12:07 ` Philippe Mathieu-Daudé via
2022-08-30 14:24 ` Peter Xu
@ 2022-09-07 0:37 ` Gavin Shan
2 siblings, 0 replies; 4+ messages in thread
From: Gavin Shan @ 2022-09-07 0:37 UTC (permalink / raw)
To: Paolo Bonzini, qemu-devel; +Cc: f4bug, Peter Xu
On 8/27/22 6:22 PM, Paolo Bonzini wrote:
> 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: Peter Xu <peterx@redhat.com>
> Cc: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@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 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)
>
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-09-07 0:38 UTC | newest]
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2022-08-27 8:22 [PATCH v2] KVM: dirty ring: add missing memory barrier Paolo Bonzini
2022-08-30 12:07 ` Philippe Mathieu-Daudé via
2022-08-30 14:24 ` Peter Xu
2022-09-07 0:37 ` Gavin Shan
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