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Date:   Thu, 3 Nov 2022 19:46:22 +0100
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Subject: Re: [PATCH 33/44] KVM: x86: Do VMX/SVM support checks directly in
 vendor code
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To:     Sean Christopherson <seanjc@google.com>
Cc:     Marc Zyngier <maz@kernel.org>, Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Eric Farman <farman@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Oliver Upton <oliver.upton@linux.dev>,
        Atish Patra <atishp@atishpatra.org>,
        David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        Fabiano Rosas <farosas@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Chao Gao <chao.gao@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Yuan Yao <yuan.yao@intel.com>
References: <20221102231911.3107438-1-seanjc@google.com>
 <20221102231911.3107438-34-seanjc@google.com>
 <bfa98587-3b36-3834-a4b9-585a0e0aa56a@redhat.com>
 <Y2QJ2TuyZImbFFvi@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <Y2QJ2TuyZImbFFvi@google.com>
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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