linux-kernel - Re: [PATCH v2 21/21] KVM:x86: Support CET supervisor shadow stack MSR access

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Date:   Thu, 4 May 2023 09:20:41 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "john.allen@....com" <john.allen@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 21/21] KVM:x86: Support CET supervisor shadow stack MSR
 access


On 5/4/2023 1:07 AM, Edgecombe, Rick P wrote:
> On Fri, 2023-04-21 at 09:46 -0400, Yang Weijiang wrote:
>> +
>> +       incpt = !is_cet_state_supported(vcpu,
>> XFEATURE_MASK_CET_KERNEL);
>> +       incpt |= !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
>> +
>> +       vmx_set_intercept_for_msr(vcpu, MSR_IA32_INT_SSP_TAB,
>> MSR_TYPE_RW, incpt);
>> +       vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP,
>> MSR_TYPE_RW, incpt);
>> +       vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP,
>> MSR_TYPE_RW, incpt);
>> +       vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP,
>> MSR_TYPE_RW, incpt);
>>   }
> Why is this tied to XFEATURE_MASK_CET_KERNEL? I don't know how the SVM
> side works, but the host kernel doesn't use this xfeature. Just not
> clear on what the intention is. Why not use
> kvm_cet_kernel_shstk_supported() again?

I don't know how SVM supports supervisor SHSTK either, here just follows 
the spec.

to add the dependency check. Maybe you're right, I need to use 
kvm_cet_kernel_shstk_supported()

in my patch set and leave the work to SVM enabling patches. I'll change 
it, thanks!