[PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

Maxim Levitsky
2020-05-23T16:15:34Z

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.

Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.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 b226fb8abe41b..4752293312947 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5316,6 +5316,10 @@ static void kvm_init_msr_list(void)
min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
continue;
break;
+ case MSR_IA32_UMWAIT_CONTROL:
+ if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
+ continue;
+ break;
default:
break;
}
--
2.26.2