On Tue, May 26, 2020 at 06:03:32PM -0700, Krish Sadhukhan wrote: > > On 5/23/20 9:14 AM, Maxim Levitsky wrote: > >On my AMD machine I noticed that I can't start any nested guests, > >because nested KVM (everything from master git branches) complains > >that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't > >support > >at all anyway. > > > >I traced it to the recently added UMWAIT support to qemu and kvm. > >The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without > >checking that it the underlying feature is supported in CPUID. > >It happened to work when non nested because as a precation kvm, > >tries to read each MSR on host before adding it to that list, > >and when read gets a #GP it ignores it. > > > >When running nested, the L1 hypervisor can be set to ignore unknown > >msr read/writes (I need this for some other guests), thus this safety > >check doesn't work anymore. > > > >V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability > > * dropped the cosmetic fix patch as it is now fixed in kvm/queue > > > >Best regards, > > Maxim Levitsky > > > >Maxim Levitsky (2): > > kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities > > kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally > > > > arch/x86/kvm/vmx/vmx.c | 3 +++ > > arch/x86/kvm/x86.c | 4 ++++ > > 2 files changed, 7 insertions(+) > > > Nit: The added 'break' statement in patch# 2 is not required.
It is unless you want to add a fallthrough annotation.
