From: Borislav Petkov <bp@alien8.de>
To: Sean Christopherson <seanjc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Jiaxi Chen <jiaxi.chen@linux.intel.com>,
kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
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, nathan@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/6] x86: KVM: Advertise CMPccXADD CPUID to user space
Date: Mon, 21 Nov 2022 16:53:04 +0100 [thread overview]
Message-ID: <Y3ue4PoJD7EGC5dV@zn.tnic> (raw)
In-Reply-To: <Y3udtm6oC7k41kaR@google.com>
On Mon, Nov 21, 2022 at 03:48:06PM +0000, Sean Christopherson wrote:
> Actually, for these features that don't require additional KVM enabling, KVM isn't
> making the feature avaiable to the guest. KVM is just advertising to userspace
> that KVM "supports" these features. Userspace ultimately controls guest CPUID;
> outside of a few special cases, KVM neither rejects nor filters unsupported bits
> in CPUID.
So is there any point to those "enable it in KVM" patches streaming constantly?
AFAICT, the only reason is to "pass through" the CPUID bit to the guest
in case KVM is not showing it in the intercepted CPUID...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-11-21 15:53 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-18 14:15 [PATCH v4 0/6] x86: KVM: Advertise CPUID of new Intel platform instructions to user space Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 1/6] x86: KVM: Advertise CMPccXADD CPUID " Jiaxi Chen
2022-11-18 16:47 ` Dave Hansen
2022-11-18 18:34 ` Borislav Petkov
2022-11-21 14:46 ` Jiaxi Chen
2022-11-21 15:29 ` Dave Hansen
2022-11-21 15:48 ` Sean Christopherson
2022-11-21 15:53 ` Borislav Petkov [this message]
2022-11-21 17:28 ` Sean Christopherson
2022-11-21 19:50 ` Borislav Petkov
2022-11-23 6:33 ` Jiaxi Chen
2022-11-21 15:38 ` Borislav Petkov
2022-11-23 7:46 ` Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 2/6] x86: KVM: Advertise AMX-FP16 " Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 3/6] x86: KVM: Advertise AVX-IFMA " Jiaxi Chen
2022-11-18 16:08 ` Sean Christopherson
2022-11-21 14:46 ` Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 4/6] x86: KVM: Advertise AVX-VNNI-INT8 " Jiaxi Chen
2022-11-18 17:17 ` Sean Christopherson
2022-11-21 15:06 ` Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 5/6] x86: KVM: Advertise AVX-NE-CONVERT " Jiaxi Chen
2022-11-18 14:15 ` [PATCH v4 6/6] x86: KVM: Advertise PREFETCHIT0/1 " Jiaxi Chen
2022-11-18 15:11 ` [PATCH v4 0/6] x86: KVM: Advertise CPUID of new Intel platform instructions " Borislav Petkov
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