* [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers
@ 2017-04-11 9:49 Wanpeng Li
2017-04-11 14:20 ` Paolo Bonzini
2017-04-12 19:04 ` Radim Krčmář
0 siblings, 2 replies; 3+ messages in thread
From: Wanpeng Li @ 2017-04-11 9:49 UTC (permalink / raw)
To: linux-kernel, kvm; +Cc: Paolo Bonzini, Radim Krčmář, Wanpeng Li
From: Wanpeng Li <wanpeng.li@hotmail.com>
virt_xxx memory barriers are implemented trivially using the low-level
__smp_xxx macros, __smp_xxx is equal to a compiler barrier for strong
TSO memory model, however, mandatory barriers will unconditional add
memory barriers, this patch replaces the rmb() in kvm_steal_clock() by
virt_rmb().
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
arch/x86/kernel/kvm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 14f65a5..da5c097 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -396,9 +396,9 @@ static u64 kvm_steal_clock(int cpu)
src = &per_cpu(steal_time, cpu);
do {
version = src->version;
- rmb();
+ virt_rmb();
steal = src->steal;
- rmb();
+ virt_rmb();
} while ((version & 1) || (version != src->version));
return steal;
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers
2017-04-11 9:49 [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers Wanpeng Li
@ 2017-04-11 14:20 ` Paolo Bonzini
2017-04-12 19:04 ` Radim Krčmář
1 sibling, 0 replies; 3+ messages in thread
From: Paolo Bonzini @ 2017-04-11 14:20 UTC (permalink / raw)
To: Wanpeng Li; +Cc: linux-kernel, kvm, Radim Krčmář, Wanpeng Li
----- Original Message -----
> From: "Wanpeng Li" <kernellwp@gmail.com>
> To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
> Cc: "Paolo Bonzini" <pbonzini@redhat.com>, "Radim Krčmář" <rkrcmar@redhat.com>, "Wanpeng Li" <wanpeng.li@hotmail.com>
> Sent: Tuesday, April 11, 2017 5:49:21 PM
> Subject: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers
>
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> virt_xxx memory barriers are implemented trivially using the low-level
> __smp_xxx macros, __smp_xxx is equal to a compiler barrier for strong
> TSO memory model, however, mandatory barriers will unconditional add
> memory barriers, this patch replaces the rmb() in kvm_steal_clock() by
> virt_rmb().
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> arch/x86/kernel/kvm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 14f65a5..da5c097 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -396,9 +396,9 @@ static u64 kvm_steal_clock(int cpu)
> src = &per_cpu(steal_time, cpu);
> do {
> version = src->version;
> - rmb();
> + virt_rmb();
> steal = src->steal;
> - rmb();
> + virt_rmb();
> } while ((version & 1) || (version != src->version));
>
> return steal;
> --
> 2.7.4
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers
2017-04-11 9:49 [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers Wanpeng Li
2017-04-11 14:20 ` Paolo Bonzini
@ 2017-04-12 19:04 ` Radim Krčmář
1 sibling, 0 replies; 3+ messages in thread
From: Radim Krčmář @ 2017-04-12 19:04 UTC (permalink / raw)
To: Wanpeng Li; +Cc: linux-kernel, kvm, Paolo Bonzini, Wanpeng Li
2017-04-11 02:49-0700, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> virt_xxx memory barriers are implemented trivially using the low-level
> __smp_xxx macros, __smp_xxx is equal to a compiler barrier for strong
> TSO memory model, however, mandatory barriers will unconditional add
> memory barriers, this patch replaces the rmb() in kvm_steal_clock() by
> virt_rmb().
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
Applied to kvm/queue, thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-04-11 9:49 [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers Wanpeng Li
2017-04-11 14:20 ` Paolo Bonzini
2017-04-12 19:04 ` Radim Krčmář
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