linux-kernel - Re: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

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Date:   Tue, 03 Mar 2020 17:12:03 +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, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

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

> Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
> shouldn't advertise features that realistically can't be used.  Use
> kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
> svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
> adjustments into common x86 code.
>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/svm.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f32fc3c03667..8e39dcd3160d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
>  	if (avic)
>  		kvm_cpu_cap_clear(X86_FEATURE_X2APIC);
>  
> -	/* CPUID 0x80000001 */
> -	if (nested)
> +	/* CPUID 0x80000001 and 0x8000000A (SVM features) */
> +	if (nested) {
>  		kvm_cpu_cap_set(X86_FEATURE_SVM);
>  
> +		if (boot_cpu_has(X86_FEATURE_NRIPS))
> +			kvm_cpu_cap_set(X86_FEATURE_NRIPS);
> +
> +		if (npt_enabled)
> +			kvm_cpu_cap_set(X86_FEATURE_NPT);
> +	}
> +
>  	/* CPUID 0x80000008 */
>  	if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
>  	    boot_cpu_has(X86_FEATURE_AMD_SSBD))
>  		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
> -
> -	/* CPUID 0x8000000A */
> -	/* Support next_rip if host supports it */
> -	kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
> -
> -	if (npt_enabled)
> -		kvm_cpu_cap_set(X86_FEATURE_NPT);
>  }
>  
>  static __init int svm_hardware_setup(void)
> @@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
>  {
>  	switch (entry->function) {
>  	case 0x8000000A:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
> +			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> +			break;
> +		}
>  		entry->eax = 1; /* SVM revision 1 */
>  		entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
>  				   ASID emulation to nested SVM */

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

-- 
Vitaly