linux-kernel - Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

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Message-ID: <674dc359b794d0380f90dbb9c7d026b605d40c12.camel@redhat.com>
Date:   Wed, 27 May 2020 18:17:40 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tao Xu <tao3.xu@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jingqi Liu <jingqi.liu@...el.com>
Subject: Re: [PATCH 0/2] Fix issue with not starting nesting guests on my
 system

On Tue, 2020-05-26 at 18:13 -0700, Sean Christopherson wrote:
> On Sat, May 23, 2020 at 07:14:53PM +0300, 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
> 
> Standard scoping in the shortlog is "KVM: VMX:" and "KVM: x86:".
Noted and I will use it from now on.
Thanks!

Best regards,
	Maxim Levitsky

> 
> >  arch/x86/kvm/vmx/vmx.c | 3 +++
> >  arch/x86/kvm/x86.c     | 4 ++++
> >  2 files changed, 7 insertions(+)
> > 
> > -- 
> > 2.26.2
> > 
> >