Re: [PATCH stable-5.4] KVM: x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/11/20 14:20, Jack Wang wrote:
> From: Maxim Levitsky <mlevitsk@redhat.com>
> 
> This msr is only available when the host supports WAITPKG feature.
> 
> This breaks a nested guest, if the L1 hypervisor is set to ignore
> unknown msrs, because the only other safety check that the
> kernel does is that it attempts to read the msr and
> rejects it if it gets an exception.
> 
> Cc: stable@vger.kernel.org
> Fixes: 6e3ba4abce ("KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL")
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> Message-Id: <20200523161455.3940-3-mlevitsk@redhat.com>
> Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> (cherry picked from commit f4cfcd2d5aea4e96c5d483c476f3057b6b7baf6a
> use boot_cpu_has for checking the feature)
> Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
> ---
>   arch/x86/kvm/x86.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 708b37274cb5..4cacf4669235 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5226,6 +5226,10 @@ static void kvm_init_msr_list(void)
>   			if (!kvm_x86_ops->rdtscp_supported())
>   				continue;
>   			break;
> +		case MSR_IA32_UMWAIT_CONTROL:
> +			if (!boot_cpu_has(X86_FEATURE_WAITPKG))
> +				continue;
> +			break;
>   		case MSR_IA32_RTIT_CTL:
>   		case MSR_IA32_RTIT_STATUS:
>   			if (!kvm_x86_ops->pt_supported())
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo