* [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg()
@ 2023-01-09 14:54 Heiko Carstens
2023-01-09 16:03 ` Claudio Imbrenda
2023-01-10 19:15 ` Christian Borntraeger
0 siblings, 2 replies; 4+ messages in thread
From: Heiko Carstens @ 2023-01-09 14:54 UTC (permalink / raw)
To: Christian Borntraeger, Janosch Frank, Claudio Imbrenda
Cc: David Hildenbrand, kvm, linux-s390, linux-kernel
Use READ_ONCE() before cmpxchg() to prevent that the compiler generates
code that fetches the to be compared old value several times from memory.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
v2: make it compile
arch/s390/kvm/interrupt.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 1dae78deddf2..ab26aa53ee37 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -83,8 +83,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
struct esca_block *sca = vcpu->kvm->arch.sca;
union esca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
- union esca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
+ union esca_sigp_ctrl new_val = {0}, old_val;
+ old_val = READ_ONCE(*sigp_ctrl);
new_val.scn = src_id;
new_val.c = 1;
old_val.c = 0;
@@ -95,8 +96,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
struct bsca_block *sca = vcpu->kvm->arch.sca;
union bsca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
- union bsca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
+ union bsca_sigp_ctrl new_val = {0}, old_val;
+ old_val = READ_ONCE(*sigp_ctrl);
new_val.scn = src_id;
new_val.c = 1;
old_val.c = 0;
@@ -126,16 +128,18 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
struct esca_block *sca = vcpu->kvm->arch.sca;
union esca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
- union esca_sigp_ctrl old = *sigp_ctrl;
+ union esca_sigp_ctrl old;
+ old = READ_ONCE(*sigp_ctrl);
expect = old.value;
rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
} else {
struct bsca_block *sca = vcpu->kvm->arch.sca;
union bsca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
- union bsca_sigp_ctrl old = *sigp_ctrl;
+ union bsca_sigp_ctrl old;
+ old = READ_ONCE(*sigp_ctrl);
expect = old.value;
rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
}
--
2.34.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg()
2023-01-09 14:54 [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg() Heiko Carstens
@ 2023-01-09 16:03 ` Claudio Imbrenda
2023-01-10 19:15 ` Christian Borntraeger
1 sibling, 0 replies; 4+ messages in thread
From: Claudio Imbrenda @ 2023-01-09 16:03 UTC (permalink / raw)
To: Heiko Carstens
Cc: Christian Borntraeger, Janosch Frank, David Hildenbrand, kvm,
linux-s390, linux-kernel
On Mon, 9 Jan 2023 15:54:56 +0100
Heiko Carstens <hca@linux.ibm.com> wrote:
> Use READ_ONCE() before cmpxchg() to prevent that the compiler generates
> code that fetches the to be compared old value several times from memory.
>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>
> v2: make it compile
>
> arch/s390/kvm/interrupt.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 1dae78deddf2..ab26aa53ee37 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -83,8 +83,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
> struct esca_block *sca = vcpu->kvm->arch.sca;
> union esca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union esca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
> + union esca_sigp_ctrl new_val = {0}, old_val;
>
> + old_val = READ_ONCE(*sigp_ctrl);
> new_val.scn = src_id;
> new_val.c = 1;
> old_val.c = 0;
> @@ -95,8 +96,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
> struct bsca_block *sca = vcpu->kvm->arch.sca;
> union bsca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union bsca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
> + union bsca_sigp_ctrl new_val = {0}, old_val;
>
> + old_val = READ_ONCE(*sigp_ctrl);
> new_val.scn = src_id;
> new_val.c = 1;
> old_val.c = 0;
> @@ -126,16 +128,18 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
> struct esca_block *sca = vcpu->kvm->arch.sca;
> union esca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union esca_sigp_ctrl old = *sigp_ctrl;
> + union esca_sigp_ctrl old;
>
> + old = READ_ONCE(*sigp_ctrl);
> expect = old.value;
> rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
> } else {
> struct bsca_block *sca = vcpu->kvm->arch.sca;
> union bsca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union bsca_sigp_ctrl old = *sigp_ctrl;
> + union bsca_sigp_ctrl old;
>
> + old = READ_ONCE(*sigp_ctrl);
> expect = old.value;
> rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
> }
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg()
2023-01-09 14:54 [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg() Heiko Carstens
2023-01-09 16:03 ` Claudio Imbrenda
@ 2023-01-10 19:15 ` Christian Borntraeger
2023-01-11 12:11 ` Heiko Carstens
1 sibling, 1 reply; 4+ messages in thread
From: Christian Borntraeger @ 2023-01-10 19:15 UTC (permalink / raw)
To: Heiko Carstens, Janosch Frank, Claudio Imbrenda
Cc: David Hildenbrand, kvm, linux-s390, linux-kernel
Am 09.01.23 um 15:54 schrieb Heiko Carstens:
> Use READ_ONCE() before cmpxchg() to prevent that the compiler generates
> code that fetches the to be compared old value several times from memory.
>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Looks sane.
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
In case you want to take it via the s390 tree:
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> ---
>
> v2: make it compile
>
> arch/s390/kvm/interrupt.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 1dae78deddf2..ab26aa53ee37 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -83,8 +83,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
> struct esca_block *sca = vcpu->kvm->arch.sca;
> union esca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union esca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
> + union esca_sigp_ctrl new_val = {0}, old_val;
>
> + old_val = READ_ONCE(*sigp_ctrl);
> new_val.scn = src_id;
> new_val.c = 1;
> old_val.c = 0;
> @@ -95,8 +96,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
> struct bsca_block *sca = vcpu->kvm->arch.sca;
> union bsca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union bsca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl;
> + union bsca_sigp_ctrl new_val = {0}, old_val;
>
> + old_val = READ_ONCE(*sigp_ctrl);
> new_val.scn = src_id;
> new_val.c = 1;
> old_val.c = 0;
> @@ -126,16 +128,18 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
> struct esca_block *sca = vcpu->kvm->arch.sca;
> union esca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union esca_sigp_ctrl old = *sigp_ctrl;
> + union esca_sigp_ctrl old;
>
> + old = READ_ONCE(*sigp_ctrl);
> expect = old.value;
> rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
> } else {
> struct bsca_block *sca = vcpu->kvm->arch.sca;
> union bsca_sigp_ctrl *sigp_ctrl =
> &(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
> - union bsca_sigp_ctrl old = *sigp_ctrl;
> + union bsca_sigp_ctrl old;
>
> + old = READ_ONCE(*sigp_ctrl);
> expect = old.value;
> rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
> }
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg()
2023-01-10 19:15 ` Christian Borntraeger
@ 2023-01-11 12:11 ` Heiko Carstens
0 siblings, 0 replies; 4+ messages in thread
From: Heiko Carstens @ 2023-01-11 12:11 UTC (permalink / raw)
To: Christian Borntraeger
Cc: Janosch Frank, Claudio Imbrenda, David Hildenbrand, kvm,
linux-s390, linux-kernel
On Tue, Jan 10, 2023 at 08:15:50PM +0100, Christian Borntraeger wrote:
> Am 09.01.23 um 15:54 schrieb Heiko Carstens:
> > Use READ_ONCE() before cmpxchg() to prevent that the compiler generates
> > code that fetches the to be compared old value several times from memory.
> >
> > Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
>
> Looks sane.
>
> Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>
> In case you want to take it via the s390 tree:
> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Given that there don't seem to be any pending s390 specific patches I
take it via the s390 tree.
Applied.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-01-11 12:11 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-01-09 14:54 [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg() Heiko Carstens
2023-01-09 16:03 ` Claudio Imbrenda
2023-01-10 19:15 ` Christian Borntraeger
2023-01-11 12:11 ` Heiko Carstens
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.