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SubjectRe: [PATCH 43/61] KVM: x86: Use KVM cpu caps to mark CR4.LA57 as not-reserved
Date
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Add accessor(s) for KVM cpu caps and use said accessor to detect
> hardware support for LA57 instead of manually querying CPUID.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/cpuid.h | 13 +++++++++++++
> arch/x86/kvm/x86.c | 2 +-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 7b71ae0ca05e..5ce4219d465f 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -274,6 +274,19 @@ static __always_inline void kvm_cpu_cap_set(unsigned x86_feature)
> kvm_cpu_caps[x86_leaf] |= __feature_bit(x86_feature);
> }
>
> +static __always_inline u32 kvm_cpu_cap_get(unsigned x86_feature)
> +{
> + unsigned x86_leaf = x86_feature / 32;
> +
> + reverse_cpuid_check(x86_leaf);
> + return kvm_cpu_caps[x86_leaf] & __feature_bit(x86_feature);
> +}
> +
> +static __always_inline bool kvm_cpu_cap_has(unsigned x86_feature)
> +{
> + return kvm_cpu_cap_get(x86_feature);
> +}

I know this works (and I even checked C99 to make sure that it works not
by accident) but I have to admit that explicit '!!' conversion to bool
always makes me feel safer :-)

> +
> static __always_inline void kvm_cpu_cap_check_and_set(unsigned x86_feature)
> {
> if (boot_cpu_has(x86_feature))
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c5ed199d6cd9..cb40737187a1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -912,7 +912,7 @@ static u64 kvm_host_cr4_reserved_bits(struct cpuinfo_x86 *c)
> {
> u64 reserved_bits = __cr4_reserved_bits(cpu_has, c);
>
> - if (cpuid_ecx(0x7) & feature_bit(LA57))
> + if (kvm_cpu_cap_has(X86_FEATURE_LA57))
> reserved_bits &= ~X86_CR4_LA57;
>
> if (kvm_x86_ops->umip_emulated())

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly

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