Re: [Patch 4/6] kvm: svm: Enumerate XSAVES in guest CPUID when it is available to the guest

[Yang Weijiang <weijiang.yang@intel.com>]

On Tue, Oct 08, 2019 at 05:41:40PM -0700, Aaron Lewis wrote:
> Add the function guest_cpuid_set() to allow a bit in the guest cpuid to
> be set.  This is complementary to the guest_cpuid_clear() function.
> 
> Also, set the XSAVES bit in the guest cpuid if the host has the same bit
> set and guest has XSAVE bit set.  This is to ensure that XSAVES will be
> enumerated in the guest CPUID if XSAVES can be used in the guest.
> 
> Reviewed-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Aaron Lewis <aaronlewis@google.com>
> ---
>  arch/x86/kvm/cpuid.h | 9 +++++++++
>  arch/x86/kvm/svm.c   | 4 ++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index d78a61408243..420ceea02fd1 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -113,6 +113,15 @@ static __always_inline void guest_cpuid_clear(struct kvm_vcpu *vcpu, unsigned x8
>  		*reg &= ~bit(x86_feature);
>  }
>  
> +static __always_inline void guest_cpuid_set(struct kvm_vcpu *vcpu, unsigned x86_feature)
> +{
> +	int *reg;
> +
> +	reg = guest_cpuid_get_register(vcpu, x86_feature);
> +	if (reg)
> +		*reg |= ~bit(x86_feature);
> +}
> +
Sounds like it's to set the bit, is it: *reg |= bit(x86_feature)?
>  static inline bool guest_cpuid_is_amd(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_cpuid_entry2 *best;
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 65223827c675..2522a467bbc0 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5887,6 +5887,10 @@ static void svm_cpuid_update(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  
> +	if (guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
> +	    boot_cpu_has(X86_FEATURE_XSAVES))
> +		guest_cpuid_set(vcpu, X86_FEATURE_XSAVES);
> +
>  	/* Update nrips enabled cache */
>  	svm->nrips_enabled = !!guest_cpuid_has(&svm->vcpu, X86_FEATURE_NRIPS);
>  
> -- 
> 2.23.0.581.g78d2f28ef7-goog