linux-kernel - Re: [PATCH v2 3/4] x86: Expose SERIALIZE for supported cpuid

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Message-ID: <17B83AD0-C4E9-451C-A691-DBB8B85C1533@zytor.com>
Date:   Tue, 14 Jul 2020 21:18:34 -0700
From:   hpa@...or.com
To:     "Zhang, Cathy" <cathy.zhang@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
CC:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de,
        ricardo.neri-calderon@...ux.intel.com, kyung.min.park@...el.com,
        jpoimboe@...hat.com, gregkh@...uxfoundation.org,
        ak@...ux.intel.com, dave.hansen@...el.com, tony.luck@...el.com,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH v2 3/4] x86: Expose SERIALIZE for supported cpuid

On July 14, 2020 5:03:31 PM PDT, "Zhang, Cathy" <cathy.zhang@...el.com> wrote:
>On 7/15/2020 7:05 AM, hpa@...or.com wrote:
>> On July 14, 2020 3:42:08 PM PDT, "Zhang, Cathy"
><cathy.zhang@...el.com> wrote:
>>> On 7/14/2020 11:00 AM, Sean Christopherson wrote:
>>>> On Tue, Jul 07, 2020 at 10:16:22AM +0800, Cathy Zhang wrote:
>>>>> SERIALIZE instruction is supported by intel processors,
>>>>> like Sapphire Rapids. Expose it in KVM supported cpuid.
>>>> Providing at least a rough overview of the instruction, e.g. its
>>> enumeration,
>>>> usage, fault rules, controls, etc... would be nice.  In isolation,
>>> the
>>>> changelog isn't remotely helpful in understanding the correctness
>of
>>> the
>>>> patch.
>>> Thanks Sean! Add it in the next version.
>>>>> Signed-off-by: Cathy Zhang <cathy.zhang@...el.com>
>>>>> ---
>>>>>    arch/x86/kvm/cpuid.c | 3 ++-
>>>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>>>>> index 8a294f9..e603aeb 100644
>>>>> --- a/arch/x86/kvm/cpuid.c
>>>>> +++ b/arch/x86/kvm/cpuid.c
>>>>> @@ -341,7 +341,8 @@ void kvm_set_cpu_caps(void)
>>>>>    	kvm_cpu_cap_mask(CPUID_7_EDX,
>>>>>    		F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
>>>>>    		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
>>>>> -		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM)
>>>>> +		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM) |
>>>>> +		F(SERIALIZE)
>>>>>    	);
>>>>>    
>>>>>    	/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software.
>*/
>>>>> -- 
>>>>> 1.8.3.1
>>>>>
>> At least that one is easy: SERIALIZE is architecturally a NOP, but
>with hard serialization, like CPUID or IRET.
>SERIALIZE does not modify registers, arithmetic flags or memory, which 
>is different with CPUID.

That's what I meant with it being an architectural NOP.
-- 
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