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From:   Maxim Levitsky <mlevitsk@redhat.com>
To:     kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Tao Xu <tao3.xu@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Jim Mattson <jmattson@google.com>,
        linux-kernel@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
        x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        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>,
        Maxim Levitsky <mlevitsk@redhat.com>
Subject: [PATCH 0/2] Fix issue with not starting nesting guests on my system
Date:   Sat, 23 May 2020 19:14:53 +0300
Message-Id: <20200523161455.3940-1-mlevitsk@redhat.com>
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On my AMD machine I noticed that I can't start any nested guests,=0D
because nested KVM (everything from master git branches) complains=0D
that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't supp=
ort=0D
at all anyway.=0D
=0D
I traced it to the recently added UMWAIT support to qemu and kvm.=0D
The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without=0D
checking that it the underlying feature is supported in CPUID.=0D
It happened to work when non nested because as a precation kvm,=0D
tries to read each MSR on host before adding it to that list,=0D
and when read gets a #GP it ignores it.=0D
=0D
When running nested, the L1 hypervisor can be set to ignore unknown=0D
msr read/writes (I need this for some other guests), thus this safety=0D
check doesn't work anymore.=0D
=0D
V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capabili=
ty=0D
    * dropped the cosmetic fix patch as it is now fixed in kvm/queue=0D
=0D
Best regards,=0D
	Maxim Levitsky=0D
=0D
Maxim Levitsky (2):=0D
  kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities=0D
  kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally=0D
=0D
 arch/x86/kvm/vmx/vmx.c | 3 +++=0D
 arch/x86/kvm/x86.c     | 4 ++++=0D
 2 files changed, 7 insertions(+)=0D
=0D
-- =0D
2.26.2=0D
=0D