linux-kernel - Re: [PATCH v2 15/15] KVM: x86/cpuid: Advertise Arch LBR feature in CPUID

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Message-ID: <5dccc4fb-1b90-326d-fb33-4e68c839a675@intel.com>
Date:   Sun, 25 Dec 2022 12:31:21 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Like Xu <like.xu.linux@...il.com>
CC:     <kan.liang@...ux.intel.com>, <wei.w.wang@...el.com>,
        <seanjc@...gle.com>, <pbonzini@...hat.com>, <jmattson@...gle.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 15/15] KVM: x86/cpuid: Advertise Arch LBR feature in
 CPUID


On 12/22/2022 7:03 PM, Like Xu wrote:
> On 25/11/2022 12:06 pm, Yang Weijiang wrote:
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 85e3df6217af..60b3c591d462 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -134,6 +134,19 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
>>           if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
>>               return -EINVAL;
>>       }
>> +    if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR)) {
>> +        best = cpuid_entry2_find(entries, nent, 0x1c, 0);
>> +        if (best) {
>> +            unsigned int eax, ebx, ecx, edx;
>> +
>> +            /* Reject user-space CPUID if depth is different from 
>> host's.*/
>
> Try to verify this in the KVM selftest, as this behavior is different 
> from the host.


Will do it.



>
>> +            cpuid_count(0x1c, 0, &eax, &ebx, &ecx, &edx); > +
>> +            if ((eax & 0xff) &&
>> +                (best->eax & 0xff) != BIT(fls(eax & 0xff) - 1))
>> +                return -EINVAL;
>> +        }
>> +    }