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Message-ID: <20200527011344.GB31696@linux.intel.com>
Date: Tue, 26 May 2020 18:13:44 -0700
From: Sean Christopherson <sean.j.christopherson@...el.com>
To: Maxim Levitsky <mlevitsk@...hat.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 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:".
>
> arch/x86/kvm/vmx/vmx.c | 3 +++
> arch/x86/kvm/x86.c | 4 ++++
> 2 files changed, 7 insertions(+)
>
> --
> 2.26.2
>
>
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