Re: [PATCH v2 23/23] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR

[Paolo Bonzini]

On 12/21/21 07:29, Liu, Jing2 wrote:
> >
> Thanks for reviewing the patches.
>
> If disable unconditionally in vmx_create_vcpu, it means even guest has
> no cpuid, the msr read is passthrough to guest and it can read a value, which
> seems strange, though spec doesn't mention the read behaviour w/o cpuid.
>
> How about disabling read interception at vmx_vcpu_after_set_cpuid?
>
> if (boot_cpu_has(X86_FEATURE_XFD) && guest_cpuid_has(vcpu, X86_FEATURE_XFD))
>          vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R, false);

Even better:

	if (boot_cpu_has(X86_FEATURE_XFD))
		vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
					  !guest_cpuid_has(vcpu, X86_FEATURE_XFD));

Thanks,

Paolo