Re: [PATCH v2 3/4] KVM: SVM: Add support for VMCB address check change

[Maxim Levitsky]

On Thu, 2021-01-21 at 01:55 -0500, Wei Huang wrote:
> New AMD CPUs have a change that checks VMEXIT intercept on special SVM
> instructions before checking their EAX against reserved memory region.
> This change is indicated by CPUID_0x8000000A_EDX[28]. If it is 1, #VMEXIT
> is triggered before #GP. KVM doesn't need to intercept and emulate #GP
> faults as #GP is supposed to be triggered.
> 
> Co-developed-by: Bandan Das <bsd@xxxxxxxxxx>
> Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
> Signed-off-by: Wei Huang <wei.huang2@xxxxxxx>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kvm/svm/svm.c             | 6 +++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 84b887825f12..ea89d6fdd79a 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -337,6 +337,7 @@
>  #define X86_FEATURE_AVIC		(15*32+13) /* Virtual Interrupt Controller */
>  #define X86_FEATURE_V_VMSAVE_VMLOAD	(15*32+15) /* Virtual VMSAVE VMLOAD */
>  #define X86_FEATURE_VGIF		(15*32+16) /* Virtual GIF */
> +#define X86_FEATURE_SVME_ADDR_CHK	(15*32+28) /* "" SVME addr check */
>  
>  /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */
>  #define X86_FEATURE_AVX512VBMI		(16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 6ed523cab068..2a12870ac71a 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -313,7 +313,8 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
>  	svm->vmcb->save.efer = efer | EFER_SVME;
>  	vmcb_mark_dirty(svm->vmcb, VMCB_CR);
>  	/* Enable #GP interception for SVM instructions */
> -	set_exception_intercept(svm, GP_VECTOR);
> +	if (!kvm_cpu_cap_has(X86_FEATURE_SVME_ADDR_CHK))
> +		set_exception_intercept(svm, GP_VECTOR);
>  
>  	return 0;
>  }
> @@ -933,6 +934,9 @@ static __init void svm_set_cpu_caps(void)
>  	    boot_cpu_has(X86_FEATURE_AMD_SSBD))
>  		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
>  
> +	if (boot_cpu_has(X86_FEATURE_SVME_ADDR_CHK))
> +		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
> +
>  	/* Enable INVPCID feature */
>  	kvm_cpu_cap_check_and_set(X86_FEATURE_INVPCID);
>  }

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky