linux-kernel - Re: [PATCH 33/44] KVM: x86: Do VMX/SVM support checks directly in vendor code

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Date:   Thu, 3 Nov 2022 19:46:22 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Atish Patra <atishp@...shpatra.org>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Chao Gao <chao.gao@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuan Yao <yuan.yao@...el.com>
Subject: Re: [PATCH 33/44] KVM: x86: Do VMX/SVM support checks directly in
 vendor code

On 11/3/22 19:35, Sean Christopherson wrote:
> It's technically required.  IA32_FEAT_CTL and thus KVM_INTEL depends on any of
> CPU_SUP_{INTEL,CENATUR,ZHAOXIN}, but init_ia32_feat_ctl() is invoked if and only
> if the actual CPU type matches one of the aforementioned CPU_SUP_*.
> 
> E.g. running a kernel built with
> 
>    CONFIG_CPU_SUP_INTEL=y
>    CONFIG_CPU_SUP_AMD=y
>    # CONFIG_CPU_SUP_HYGON is not set
>    # CONFIG_CPU_SUP_CENTAUR is not set
>    # CONFIG_CPU_SUP_ZHAOXIN is not set
> 
> on a Cenatur or Zhaoxin CPU will leave X86_FEATURE_VMX set but not set
> X86_FEATURE_MSR_IA32_FEAT_CTL.  If VMX isn't enabled in MSR_IA32_FEAT_CTL, KVM
> will get unexpected #UDs when trying to enable VMX.

Oh, I see.  Perhaps X86_FEATURE_VMX and X86_FEATURE_SGX should be moved 
to one of the software words instead of using cpuid.  Nothing that you 
should care about for this series though.

Paolo