Re: [PATCH v7 09/27] KVM: arm64: Add a vcpu flag to control SVE visibility for the guest
On Fri, Mar 29, 2019 at 01:00:34PM +, Dave Martin wrote:
> Since SVE will be enabled or disabled on a per-vcpu basis, a flag
> is needed in order to track which vcpus have it enabled.
>
> This patch adds a suitable flag and a helper for checking it.
>
> Signed-off-by: Dave Martin
> Reviewed-by: Alex Bennée
> Tested-by: zhang.lei
> ---
> arch/arm64/include/asm/kvm_host.h | 4
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index 6d10100..ad4f7f0 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -328,6 +328,10 @@ struct kvm_vcpu_arch {
> #define KVM_ARM64_FP_HOST(1 << 2) /* host FP regs loaded */
> #define KVM_ARM64_HOST_SVE_IN_USE(1 << 3) /* backup for host TIF_SVE */
> #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */
> +#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to
> guest */
> +
> +#define vcpu_has_sve(vcpu) (system_supports_sve() && \
> + ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
>
> #define vcpu_gp_regs(v) (&(v)->arch.ctxt.gp_regs)
>
> --
> 2.1.4
>
Reviewed-by: Andrew Jones
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Re: [PATCH v7 09/27] KVM: arm64: Add a vcpu flag to control SVE visibility for the guest
On Thu, Apr 04, 2019 at 04:17:24AM +0100, Marc Zyngier wrote:
> On Wed, 03 Apr 2019 20:14:13 +0100,
> Andrew Jones wrote:
> >
> > On Fri, Mar 29, 2019 at 01:00:34PM +, Dave Martin wrote:
> > > Since SVE will be enabled or disabled on a per-vcpu basis, a flag
> > > is needed in order to track which vcpus have it enabled.
> > >
> > > This patch adds a suitable flag and a helper for checking it.
> > >
> > > Signed-off-by: Dave Martin
> > > Reviewed-by: Alex Bennée
> > > Tested-by: zhang.lei
> > > ---
> > > arch/arm64/include/asm/kvm_host.h | 4
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/arch/arm64/include/asm/kvm_host.h
> > > b/arch/arm64/include/asm/kvm_host.h
> > > index 6d10100..ad4f7f0 100644
> > > --- a/arch/arm64/include/asm/kvm_host.h
> > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > @@ -328,6 +328,10 @@ struct kvm_vcpu_arch {
> > > #define KVM_ARM64_FP_HOST(1 << 2) /* host FP regs loaded
> > > */
> > > #define KVM_ARM64_HOST_SVE_IN_USE(1 << 3) /* backup for host
> > > TIF_SVE */
> > > #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0
> > > */
> > > +#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to
> > > guest */
> > > +
> > > +#define vcpu_has_sve(vcpu) (system_supports_sve() && \
> > > + ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
> >
> > We shouldn't need the system_supports_sve() here. vcpu->arch.flags can
> > only have the KVM_ARM64_GUEST_HAS_SVE flag set when system_supports_sve()
> > is true, and it can't change later.
>
> This is a performance optimisation. system_supports_sve() results in a
> static key being emitted, and that avoids a number of loads on the
> fast path for non-SVE systems (which is likely to be the absolute
> majority for the foreseeable future).
Exactly so. The same applies to many of the other call sites for
system_supports_sve().
Cheers
---Dave
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Re: [PATCH v7 09/27] KVM: arm64: Add a vcpu flag to control SVE visibility for the guest
On Wed, 03 Apr 2019 20:14:13 +0100,
Andrew Jones wrote:
>
> On Fri, Mar 29, 2019 at 01:00:34PM +, Dave Martin wrote:
> > Since SVE will be enabled or disabled on a per-vcpu basis, a flag
> > is needed in order to track which vcpus have it enabled.
> >
> > This patch adds a suitable flag and a helper for checking it.
> >
> > Signed-off-by: Dave Martin
> > Reviewed-by: Alex Bennée
> > Tested-by: zhang.lei
> > ---
> > arch/arm64/include/asm/kvm_host.h | 4
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index 6d10100..ad4f7f0 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -328,6 +328,10 @@ struct kvm_vcpu_arch {
> > #define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded */
> > #define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host TIF_SVE */
> > #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */
> > +#define KVM_ARM64_GUEST_HAS_SVE(1 << 5) /* SVE exposed to
> > guest */
> > +
> > +#define vcpu_has_sve(vcpu) (system_supports_sve() && \
> > + ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
>
> We shouldn't need the system_supports_sve() here. vcpu->arch.flags can
> only have the KVM_ARM64_GUEST_HAS_SVE flag set when system_supports_sve()
> is true, and it can't change later.
This is a performance optimisation. system_supports_sve() results in a
static key being emitted, and that avoids a number of loads on the
fast path for non-SVE systems (which is likely to be the absolute
majority for the foreseeable future).
Thanks,
M.
--
Jazz is not dead, it just smell funny.
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Re: [PATCH v7 09/27] KVM: arm64: Add a vcpu flag to control SVE visibility for the guest
On Fri, Mar 29, 2019 at 01:00:34PM +, Dave Martin wrote:
> Since SVE will be enabled or disabled on a per-vcpu basis, a flag
> is needed in order to track which vcpus have it enabled.
>
> This patch adds a suitable flag and a helper for checking it.
>
> Signed-off-by: Dave Martin
> Reviewed-by: Alex Bennée
> Tested-by: zhang.lei
> ---
> arch/arm64/include/asm/kvm_host.h | 4
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h
> b/arch/arm64/include/asm/kvm_host.h
> index 6d10100..ad4f7f0 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -328,6 +328,10 @@ struct kvm_vcpu_arch {
> #define KVM_ARM64_FP_HOST(1 << 2) /* host FP regs loaded */
> #define KVM_ARM64_HOST_SVE_IN_USE(1 << 3) /* backup for host TIF_SVE */
> #define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */
> +#define KVM_ARM64_GUEST_HAS_SVE (1 << 5) /* SVE exposed to
> guest */
> +
> +#define vcpu_has_sve(vcpu) (system_supports_sve() && \
> + ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
We shouldn't need the system_supports_sve() here. vcpu->arch.flags can
only have the KVM_ARM64_GUEST_HAS_SVE flag set when system_supports_sve()
is true, and it can't change later.
Thanks,
drew
>
> #define vcpu_gp_regs(v) (&(v)->arch.ctxt.gp_regs)
>
> --
> 2.1.4
>
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[PATCH v7 09/27] KVM: arm64: Add a vcpu flag to control SVE visibility for the guest
Since SVE will be enabled or disabled on a per-vcpu basis, a flag
is needed in order to track which vcpus have it enabled.
This patch adds a suitable flag and a helper for checking it.
Signed-off-by: Dave Martin
Reviewed-by: Alex Bennée
Tested-by: zhang.lei
---
arch/arm64/include/asm/kvm_host.h | 4
1 file changed, 4 insertions(+)
diff --git a/arch/arm64/include/asm/kvm_host.h
b/arch/arm64/include/asm/kvm_host.h
index 6d10100..ad4f7f0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -328,6 +328,10 @@ struct kvm_vcpu_arch {
#define KVM_ARM64_FP_HOST (1 << 2) /* host FP regs loaded */
#define KVM_ARM64_HOST_SVE_IN_USE (1 << 3) /* backup for host TIF_SVE */
#define KVM_ARM64_HOST_SVE_ENABLED (1 << 4) /* SVE enabled for EL0 */
+#define KVM_ARM64_GUEST_HAS_SVE(1 << 5) /* SVE exposed to
guest */
+
+#define vcpu_has_sve(vcpu) (system_supports_sve() && \
+ ((vcpu)->arch.flags & KVM_ARM64_GUEST_HAS_SVE))
#define vcpu_gp_regs(v)(&(v)->arch.ctxt.gp_regs)
--
2.1.4
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