Messages in this thread | | | Subject | Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally | From | Xiaoyao Li <> | Date | Thu, 21 May 2020 12:33:29 +0800 |
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On 5/21/2020 5:05 AM, Paolo Bonzini wrote: > 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);
+ Tao
I remember there is certainly some reason why we don't expose WAITPKG to guest by default.
Tao, please help clarify it.
Thanks, -Xiaoyao
> > in vmx_set_cpu_caps. > > Thanks, > > Paolo >
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