Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <2e2cca1f7eab64dc55d3ac306f92f9f8318fc775.camel@redhat.com>
Subject: Re: [PATCH 0/2] Fix issue with not starting nesting guests on my
 system
From:   Maxim Levitsky <mlevitsk@redhat.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Tao Xu <tao3.xu@intel.com>,
        Jim Mattson <jmattson@google.com>,
        linux-kernel@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Wanpeng Li <wanpengli@tencent.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jingqi Liu <jingqi.liu@intel.com>
Date:   Wed, 27 May 2020 18:17:24 +0300
In-Reply-To: <20200527011344.GB31696@linux.intel.com>
References: <20200523161455.3940-1-mlevitsk@redhat.com>
         <20200527011344.GB31696@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.36.2 (3.36.2-1.fc32) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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:".
This another thing I usually mess up in the commit messages.
Fixed and noted for futher patches 

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