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

[Sasha Levin <sashal@kernel.org>]

On Wed, Nov 11, 2020 at 02:51:12PM +0100, Paolo Bonzini wrote:
>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>

Queued up, thanks!

-- 
Thanks,
Sasha