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

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Message-ID: <95c3cce88560024566f3b4b0061ca7e62a8a4286.camel@intel.com>
Date:   Tue, 15 Nov 2022 22:50:58 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "farman@...ux.ibm.com" <farman@...ux.ibm.com>,
        "chenhuacai@...nel.org" <chenhuacai@...nel.org>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "anup@...infault.org" <anup@...infault.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "borntraeger@...ux.ibm.com" <borntraeger@...ux.ibm.com>,
        "aleksandar.qemu.devel@...il.com" <aleksandar.qemu.devel@...il.com>,
        "frankja@...ux.ibm.com" <frankja@...ux.ibm.com>
CC:     "oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Yao, Yuan" <yuan.yao@...el.com>,
        "farosas@...ux.ibm.com" <farosas@...ux.ibm.com>,
        "david@...hat.com" <david@...hat.com>,
        "james.morse@....com" <james.morse@....com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "alexandru.elisei@....com" <alexandru.elisei@....com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "kvm-riscv@...ts.infradead.org" <kvm-riscv@...ts.infradead.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "Gao, Chao" <chao.gao@...el.com>,
        "atishp@...shpatra.org" <atishp@...shpatra.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 33/44] KVM: x86: Do VMX/SVM support checks directly in
 vendor code

On Wed, 2022-11-02 at 23:19 +0000, Sean Christopherson wrote:
> +static bool __init kvm_is_vmx_supported(void)
> +{
> +	if (!cpu_has_vmx()) {
> +		pr_err("CPU doesn't support VMX\n");
> +		return false;
> +	}
> +
> +	if (!boot_cpu_has(X86_FEATURE_MSR_IA32_FEAT_CTL) ||
> +	    !boot_cpu_has(X86_FEATURE_VMX)) {
> +		pr_err("VMX not enabled in MSR_IA32_FEAT_CTL\n");
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
>  static int __init vmx_check_processor_compat(void)
>  {
>  	struct vmcs_config vmcs_conf;
>  	struct vmx_capability vmx_cap;
>  
> -	if (!this_cpu_has(X86_FEATURE_MSR_IA32_FEAT_CTL) ||
> -	    !this_cpu_has(X86_FEATURE_VMX)) {
> -		pr_err("VMX is disabled on CPU %d\n", smp_processor_id());
> +	if (!kvm_is_vmx_supported())
>  		return -EIO;
> -	}
>  

Looks there's a functional change here -- the old code checks local cpu's
feature bits but the new code always checks bsp's feature bits.  Should have no
problem I think, though.