2023-06-02 01:12:21

by Sean Christopherson

Subject: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

Replace an #ifdef on CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS with a
cpu_feature_enabled() check on X86_FEATURE_PKU. The macro magic of
DISABLED_MASK_BIT_SET() means that cpu_feature_enabled() provides the
same end result (no code generated) when PKU is disabled by Kconfig.

No functional change intended.

Cc: Jon Kohler <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/x86.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ceb7c5e9cf9e..eed1f0629023 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1017,13 +1017,11 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
wrmsrl(MSR_IA32_XSS, vcpu->arch.ia32_xss);
}

-#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
- if (static_cpu_has(X86_FEATURE_PKU) &&
+ if (cpu_feature_enabled(X86_FEATURE_PKU) &&
vcpu->arch.pkru != vcpu->arch.host_pkru &&
((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE)))
write_pkru(vcpu->arch.pkru);
-#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
}
EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);

@@ -1032,15 +1030,13 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
if (vcpu->arch.guest_state_protected)
return;

-#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
- if (static_cpu_has(X86_FEATURE_PKU) &&
+ if (cpu_feature_enabled(X86_FEATURE_PKU) &&
((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
vcpu->arch.pkru = rdpkru();
if (vcpu->arch.pkru != vcpu->arch.host_pkru)
write_pkru(vcpu->arch.host_pkru);
}
-#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */

if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {


base-commit: a053a0e4a9f8c52f3acf8a9d2520c4bf39077a7e
--
2.41.0.rc2.161.g9c6817b8e7-goog

2023-06-02 16:04:16

by Jon Kohler

Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

> On Jun 1, 2023, at 9:05 PM, Sean Christopherson <[email protected]> wrote:
>
> Replace an #ifdef on CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS with a
> cpu_feature_enabled() check on X86_FEATURE_PKU. The macro magic of
> DISABLED_MASK_BIT_SET() means that cpu_feature_enabled() provides the
> same end result (no code generated) when PKU is disabled by Kconfig.
>
> No functional change intended.
>
> Cc: Jon Kohler <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/x86.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ceb7c5e9cf9e..eed1f0629023 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1017,13 +1017,11 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
> wrmsrl(MSR_IA32_XSS, vcpu->arch.ia32_xss);
> }
>
> -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> - if (static_cpu_has(X86_FEATURE_PKU) &&
> + if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> vcpu->arch.pkru != vcpu->arch.host_pkru &&
> ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE)))
> write_pkru(vcpu->arch.pkru);
> -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> }
> EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
>
> @@ -1032,15 +1030,13 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
> if (vcpu->arch.guest_state_protected)
> return;
>
> -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> - if (static_cpu_has(X86_FEATURE_PKU) &&
> + if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
> vcpu->arch.pkru = rdpkru();
> if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> write_pkru(vcpu->arch.host_pkru);
> }
> -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
>
> if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
>
>
> base-commit: a053a0e4a9f8c52f3acf8a9d2520c4bf39077a7e
> --
> 2.41.0.rc2.161.g9c6817b8e7-goog
>

Thanks for the cleanup!

Reviewed-by: Jon Kohler <[email protected]>

2023-06-02 18:43:44

by Jim Mattson

Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

On Fri, Jun 2, 2023 at 8:51 AM Jon Kohler <[email protected]> wrote:
>
>
>
> > On Jun 1, 2023, at 9:05 PM, Sean Christopherson <[email protected]> wrote:
> >
> > Replace an #ifdef on CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS with a
> > cpu_feature_enabled() check on X86_FEATURE_PKU. The macro magic of
> > DISABLED_MASK_BIT_SET() means that cpu_feature_enabled() provides the
> > same end result (no code generated) when PKU is disabled by Kconfig.
> >
> > No functional change intended.
> >
> > Cc: Jon Kohler <[email protected]>
> > Signed-off-by: Sean Christopherson <[email protected]>
> > ---
> > arch/x86/kvm/x86.c | 8 ++------
> > 1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ceb7c5e9cf9e..eed1f0629023 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1017,13 +1017,11 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
> > wrmsrl(MSR_IA32_XSS, vcpu->arch.ia32_xss);
> > }
> >
> > -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> > - if (static_cpu_has(X86_FEATURE_PKU) &&
> > + if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> > vcpu->arch.pkru != vcpu->arch.host_pkru &&
> > ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> > kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE)))
> > write_pkru(vcpu->arch.pkru);
> > -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> > }
> > EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
> >
> > @@ -1032,15 +1030,13 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
> > if (vcpu->arch.guest_state_protected)
> > return;
> >
> > -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> > - if (static_cpu_has(X86_FEATURE_PKU) &&
> > + if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> > ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> > kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
> > vcpu->arch.pkru = rdpkru();
> > if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> > write_pkru(vcpu->arch.host_pkru);
> > }
> > -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> >
> > if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
> >
> >
> > base-commit: a053a0e4a9f8c52f3acf8a9d2520c4bf39077a7e
> > --
> > 2.41.0.rc2.161.g9c6817b8e7-goog
> >
>
> Thanks for the cleanup!
>
> Reviewed-by: Jon Kohler <[email protected]>

+Mingwei Zhang

As we move towards enabling PKRU on the host, due to some customer
requests, I have to wonder if PKRU-disabled is the norm.

In other words, is this a likely() or unlikely() optimization?

2023-06-02 21:11:36

by Mingwei Zhang

Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

>
> As we move towards enabling PKRU on the host, due to some customer
> requests, I have to wonder if PKRU-disabled is the norm.
>
> In other words, is this a likely() or unlikely() optimization?

I think it should be likely() as PKU was introduced very early in the
Skylake-SP server cores many years ago. Today I think all recent
client CPUs should have PKU on default if I am not mistaken. So yeah,
adding a likely() probably should help prevent the compiler from
evicting this code chunk to the end of function.

Thanks.
-Mingwei

2023-06-02 21:51:49

by Sean Christopherson

Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

On Fri, Jun 02, 2023, Jim Mattson wrote:
> On Fri, Jun 2, 2023 at 8:51 AM Jon Kohler <[email protected]> wrote:
> > > On Jun 1, 2023, at 9:05 PM, Sean Christopherson <[email protected]> wrote:
> > > @@ -1032,15 +1030,13 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
> > > if (vcpu->arch.guest_state_protected)
> > > return;
> > >
> > > -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> > > - if (static_cpu_has(X86_FEATURE_PKU) &&
> > > + if (cpu_feature_enabled(X86_FEATURE_PKU) &&
> > > ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
> > > kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
> > > vcpu->arch.pkru = rdpkru();
> > > if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> > > write_pkru(vcpu->arch.host_pkru);
> > > }
> > > -#endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
> > >
> > > if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
> > >
> > >
> > > base-commit: a053a0e4a9f8c52f3acf8a9d2520c4bf39077a7e
> > > --
> > > 2.41.0.rc2.161.g9c6817b8e7-goog
> > >
> >
> > Thanks for the cleanup!
> >
> > Reviewed-by: Jon Kohler <[email protected]>
>
> +Mingwei Zhang
>
> As we move towards enabling PKRU on the host, due to some customer
> requests, I have to wonder if PKRU-disabled is the norm.
>
> In other words, is this a likely() or unlikely() optimization?

Neither? I don't see any reason to speculate on guest state. I'll bet dollars
to donuts that adding (un)likely() is negligible in terms of performance.

2023-06-07 01:02:50

by Sean Christopherson

Subject: Re: [PATCH] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef

On Thu, 01 Jun 2023 18:05:50 -0700, Sean Christopherson wrote:
> Replace an #ifdef on CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS with a
> cpu_feature_enabled() check on X86_FEATURE_PKU. The macro magic of
> DISABLED_MASK_BIT_SET() means that cpu_feature_enabled() provides the
> same end result (no code generated) when PKU is disabled by Kconfig.
>
> No functional change intended.
>
> [...]

Applied to kvm-x86 misc, thanks!

[1/1] KVM: x86: Use cpu_feature_enabled() for PKU instead of #ifdef
https://github.com/kvm-x86/linux/commit/056b9919a16a

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes