linux-kernel - Re: [PATCH 37/61] KVM: x86: Refactor handling of XSAVES CPUID adjustment

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Message-ID: <87k14cngf8.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 16:39:07 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 37/61] KVM: x86: Refactor handling of XSAVES CPUID adjustment

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Invert the handling of XSAVES, i.e. set it based on boot_cpu_has() by
> default, in preparation for adding KVM cpu caps, which will generate the
> mask at load time before ->xsaves_supported() is ready.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c74253202af8..20a7af320291 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -422,7 +422,6 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  	unsigned f_gbpages = 0;
>  	unsigned f_lm = 0;
>  #endif
> -	unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;
>  	unsigned f_intel_pt = kvm_x86_ops->pt_supported() ? F(INTEL_PT) : 0;
>  
>  	/* cpuid 1.edx */
> @@ -479,7 +478,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  
>  	/* cpuid 0xD.1.eax */
>  	const u32 kvm_cpuid_D_1_eax_x86_features =
> -		F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | f_xsaves;
> +		F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES);
>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> @@ -610,6 +609,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  
>  		entry->eax &= kvm_cpuid_D_1_eax_x86_features;
>  		cpuid_entry_mask(entry, CPUID_D_1_EAX);
> +
> +		if (!kvm_x86_ops->xsaves_supported())
> +			cpuid_entry_clear(entry, X86_FEATURE_XSAVES);
> +
>  		if (entry->eax & (F(XSAVES)|F(XSAVEC)))
>  			entry->ebx = xstate_required_size(supported_xcr0, true);
>  		else

I was going to ask if this can be moved to set_supported_cpuid() for
both VMX and SVM but then I realized this is just a temporary change.

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

-- 
Vitaly