Messages in this thread | | | Subject | Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally | From | Paolo Bonzini <> | Date | Wed, 20 May 2020 23:05:17 +0200 |
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On 20/05/20 18:07, Maxim Levitsky wrote: > 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 fe3a24fd6b263..9c507b32b1b77 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5314,6 +5314,10 @@ static void kvm_init_msr_list(void) > if (msrs_to_save_all[i] - MSR_ARCH_PERFMON_EVENTSEL0 >= > 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; > default: > break; > }
The patch is correct, and matches what is done for the other entries of msrs_to_save_all. However, while looking at it I noticed that X86_FEATURE_WAITPKG is actually never added, and that is because it was also not added to the supported CPUID in commit e69e72faa3a0 ("KVM: x86: Add support for user wait instructions", 2019-09-24), which was before the kvm_cpu_cap mechanism was added.
So while at it you should also fix that. The right way to do that is to add a
if (vmx_waitpkg_supported()) kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
in vmx_set_cpu_caps.
Thanks,
Paolo
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