linux-kernel - Re: [PATCH v3 13/21] KVM:VMX: Emulate reads and writes to CET MSRs

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Date:   Wed, 24 May 2023 10:49:59 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <rppt@...nel.org>, <rick.p.edgecombe@...el.com>,
        <john.allen@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v3 13/21] KVM:VMX: Emulate reads and writes to CET MSRs


On 5/23/2023 4:21 PM, Binbin Wu wrote:
>
>
> On 5/11/2023 12:08 PM, Yang Weijiang wrote:
>> Add support for emulating read and write accesses to CET MSRs.
>> CET MSRs are universally "special" as they are either context switched
>> via dedicated VMCS fields or via XSAVES, i.e. no additional in-memory
>> tracking is needed, but emulated reads/writes are more expensive.
[...]
>> +
>> +    if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
>> +        !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
>> +        return false;
>> +
>> +    if (msr->index == MSR_IA32_PL3_SSP &&
>> +        !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
>> +        return false;
> It may be better to merge the two if statements into one to avoid 
> calling guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) twice.
>
Yeah, it sounds good to me, thanks!

> e.g,
>
>     if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
>         (!guest_cpuid_has(vcpu, X86_FEATURE_IBT) || msr->index == 
> MSR_IA32_PL3_SSP))
>         return false;
>
>
>> +
>> +    return true;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_cet_is_msr_accessible);
>> +
>>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
>>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
>>   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
>>
> ...