linux-kernel - Re: [PATCH v3 2/6] KVM: x86: Introduce CPUID_8000_0007

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Message-ID: <8735clp2dq.fsf@redhat.com>
Date:   Wed, 21 Sep 2022 10:17:53 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] KVM: x86: Introduce CPUID_8000_0007_EDX
 'scattered' leaf

Sean Christopherson <seanjc@...gle.com> writes:

> On Fri, Sep 16, 2022, Vitaly Kuznetsov wrote:
>> CPUID_8000_0007_EDX may come handy when X86_FEATURE_CONSTANT_TSC
>> needs to be checked.
>> 
>> No functional change intended.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  arch/x86/kvm/cpuid.c         | 4 ++++
>>  arch/x86/kvm/reverse_cpuid.h | 9 ++++++++-
>>  2 files changed, 12 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 75dcf7a72605..f68b14053c9b 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -669,6 +669,10 @@ void kvm_set_cpu_caps(void)
>>  	if (!tdp_enabled && IS_ENABLED(CONFIG_X86_64))
>>  		kvm_cpu_cap_set(X86_FEATURE_GBPAGES);
>>  
>> +	kvm_cpu_cap_init_scattered(CPUID_8000_0007_EDX,
>> +		SF(CONSTANT_TSC)
>> +	);
>
> The scattered leaf needs to be used in __do_cpuid_func(), e.g.
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index ffdc28684cb7..c91f23bb3605 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1137,8 +1137,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>                 /* L2 cache and TLB: pass through host info. */
>                 break;
>         case 0x80000007: /* Advanced power management */
> -               /* invariant TSC is CPUID.80000007H:EDX[8] */
> -               entry->edx &= (1 << 8);
> +               cpuid_entry_override(entry, CPUID_8000_0007_EDX);
> +

Ah, missed that part! Will add.

>                 /* mask against host */
>                 entry->edx &= boot_cpu_data.x86_power;
>                 entry->eax = entry->ebx = entry->ecx = 0;
>

-- 
Vitaly