From: "Chen, Jiaxi" <jiaxi.chen@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, pbonzini@redhat.com, ndesaulniers@google.com,
alexandre.belloni@bootlin.com, peterz@infradead.org,
jpoimboe@kernel.org, chang.seok.bae@intel.com,
pawan.kumar.gupta@linux.intel.com, babu.moger@amd.com,
jmattson@google.com, sandipan.das@amd.com, tony.luck@intel.com,
sathyanarayanan.kuppuswamy@linux.intel.com, fenghua.yu@intel.com,
keescook@chromium.org, jane.malalane@citrix.com,
nathan@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] x86: KVM: Enable CMPccXADD CPUID and expose it to guest
Date: Thu, 20 Oct 2022 15:27:56 +0800 [thread overview]
Message-ID: <cd225cb6-9b74-4dca-bb35-6bde5e80701e@linux.intel.com> (raw)
In-Reply-To: <Y1AUhlwWjIkKfZHA@google.com>
在 2022/10/19 23:15, Sean Christopherson 写道:
> For all the shortlogs, "expose it to guest" is technically wrong. Adding
> recognition in kvm/cpuid.c advertises KVM support to host userspace. Whether or
> not a feature is exposed to the guest is up to the userspace VMM.
Thanks for reminding. How about to change the subject to this:
x86: KVM: Advertise CMPccXADD CPUID to userspace
>
> On Wed, Oct 19, 2022, Jiaxi Chen wrote:
>> CMPccXADD is a new set of instructions in the latest Intel platform Sierra
>> Forest. It includes a semaphore operation that can compare and add the
>
> In general, avoid pronouns in changelogs, it's not clear what "it" refers to here.
>
Will change it to: 'This new instruction set' here and avoid use pronouns in
the future commit message.
> And for all of these changelogs, please explicitly state that there are no VMX
> controls for these instructions, assuming that's actually true. From a KVM
> perspective, that's far more interesting than the details of the instruction(s).
>
Yes, thanks for comments. Will change this patch series to:
This instruction has no other VMX control except for exposed to userspace.
>> operands if condition is met, which can improve database performance.
>>
>> The bit definition:
>> CPUID.(EAX=7,ECX=1):EAX[bit 7]
>>
>> This patch enables this CPUID in the kernel feature bits and expose it to
>> guest OS.
>
> Same thing here, KVM doesn't decide whether or not to expose the feature to the
> guest.
>
Applied.Thanks.
>> Signed-off-by: Jiaxi Chen <jiaxi.chen@linux.intel.com>
>> ---
>> arch/x86/include/asm/cpufeatures.h | 1 +
>> arch/x86/kvm/cpuid.c | 2 +-
>> 2 files changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index ef4775c6db01..445626cb5779 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -308,6 +308,7 @@
>> /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
>> #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */
>> #define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */
>> +#define X86_FEATURE_CMPCCXADD (12*32+ 7) /* CMPccXADD instructions */
>
> Boris,
>
> What do you think about moving CPUID_7_1_EAX to be a KVM-only leaf too? AFAICT,
> KVM passthrough is the only reason the existing features are defined.
next prev parent reply other threads:[~2022-10-20 7:28 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 8:47 [PATCH 0/6] x86: KVM: Expose CPUID to guest for new Intel platform instructions Jiaxi Chen
2022-10-19 8:47 ` [PATCH 1/6] x86: KVM: Enable CMPccXADD CPUID and expose it to guest Jiaxi Chen
2022-10-19 15:15 ` Sean Christopherson
2022-10-20 7:27 ` Chen, Jiaxi [this message]
2022-10-26 3:40 ` Jiaxi Chen
2022-10-26 17:15 ` Borislav Petkov
2022-10-27 2:27 ` Jiaxi Chen
2022-11-01 9:07 ` Jiaxi Chen
2022-11-01 15:07 ` Sean Christopherson
2022-11-03 2:35 ` Jiaxi Chen
2022-10-19 8:47 ` [PATCH 2/6] x86: KVM: Enable AMX-FP16 " Jiaxi Chen
2022-11-02 18:14 ` Dave Hansen
2022-11-02 18:16 ` Paolo Bonzini
2022-11-02 18:21 ` Dave Hansen
2022-11-03 2:38 ` Jiaxi Chen
2022-10-19 8:47 ` [PATCH 3/6] x86: KVM: Enable AVX-IFMA " Jiaxi Chen
2022-10-19 8:47 ` [PATCH 4/6] x86: KVM: Enable AVX-VNNI-INT8 " Jiaxi Chen
2022-10-19 8:52 ` Borislav Petkov
2022-10-19 14:57 ` Sean Christopherson
2022-10-19 15:09 ` Sean Christopherson
2022-10-26 3:33 ` Jiaxi Chen
2022-10-20 7:13 ` Chen, Jiaxi
2022-10-19 8:47 ` [PATCH 5/6] x86: KVM: Enable AVX-NE-CONVERT " Jiaxi Chen
2022-10-19 8:47 ` [PATCH 6/6] x86: KVM: Enable PREFETCHIT0/1 " Jiaxi Chen
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