linux-kernel - Re: [PATCH v3 05/27] KVM: VMX: Disable FRED if FRED consistency checks fail

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Message-ID: <332870de-888a-4ebc-9ca5-d4980f79b8be@zytor.com>
Date: Tue, 22 Oct 2024 09:21:28 -0700
From: Xin Li <xin@...or.com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, seanjc@...gle.com, pbonzini@...hat.com,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        luto@...nel.org, peterz@...radead.org, andrew.cooper3@...rix.com
Subject: Re: [PATCH v3 05/27] KVM: VMX: Disable FRED if FRED consistency
 checks fail

On 10/22/2024 1:48 AM, Chao Gao wrote:
> On Mon, Sep 30, 2024 at 10:00:48PM -0700, Xin Li (Intel) wrote:
>> From: Xin Li <xin3.li@...el.com>
>>
>> Do not virtualize FRED if FRED consistency checks fail.
>>
>> Either on broken hardware, or when run KVM on top of another hypervisor
>> before the underlying hypervisor implements nested FRED correctly.
>>
>> Suggested-by: Chao Gao <chao.gao@...el.com>
>> Signed-off-by: Xin Li <xin3.li@...el.com>
>> Signed-off-by: Xin Li (Intel) <xin@...or.com>
>> Tested-by: Shan Kang <shan.kang@...el.com>
> 
> Reviewed-by: Chao Gao <chao.gao@...el.com>
> 
> one nit below,
> 
>> ---
>> arch/x86/kvm/vmx/capabilities.h | 7 +++++++
>> arch/x86/kvm/vmx/vmx.c          | 3 +++
>> 2 files changed, 10 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
>> index e8f3ad0f79ee..2962a3bb9747 100644
>> --- a/arch/x86/kvm/vmx/capabilities.h
>> +++ b/arch/x86/kvm/vmx/capabilities.h
>> @@ -400,6 +400,13 @@ static inline bool vmx_pebs_supported(void)
>> 	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
>> }
>>
>> +static inline bool cpu_has_vmx_fred(void)
>> +{
>> +	/* No need to check FRED VM exit controls. */
> 
> how about:
> 
> 	/*
> 	 * setup_vmcs_config() guarantees FRED VM-entry/exit controls are
> 	 * either all set or none. So, no need to check FRED VM-exit controls.
> 	 */
> 
> It is better to call out the reason.
> 

make sense!