linux-kernel - Re: [PATCH v6 13/25] KVM: x86: Initialize kvm_caps.supported

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Message-ID: <3f704ac87db03493a1d1bf8b7ae74b5a586ddbaf.camel@redhat.com>
Date:   Tue, 31 Oct 2023 19:51:13 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...el.com, peterz@...radead.org, chao.gao@...el.com,
        rick.p.edgecombe@...el.com, john.allen@....com
Subject: Re: [PATCH v6 13/25] KVM: x86: Initialize kvm_caps.supported_xss

On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
> XSAVES is supported. host_xss contains the host supported xstate feature
> bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
> enabled XSS feature bits, the resulting value represents the supervisor
> xstates that are available to guest and are backed by host FPU framework
> for swapping {guest,host} XSAVE-managed registers/MSRs.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/x86.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a616d84bd39..66edbed25db8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -226,6 +226,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>  				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>  				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>  
> +#define KVM_SUPPORTED_XSS     0
> +
>  u64 __read_mostly host_efer;
>  EXPORT_SYMBOL_GPL(host_efer);
>  
> @@ -9515,12 +9517,13 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>  		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
>  		kvm_caps.supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
>  	}
> +	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> +		rdmsrl(MSR_IA32_XSS, host_xss);
> +		kvm_caps.supported_xss = host_xss & KVM_SUPPORTED_XSS;
> +	}
>  
>  	rdmsrl_safe(MSR_EFER, &host_efer);
>  
> -	if (boot_cpu_has(X86_FEATURE_XSAVES))
> -		rdmsrl(MSR_IA32_XSS, host_xss);
> -
>  	kvm_init_pmu_capability(ops->pmu_ops);
>  
>  	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))


Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky