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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id ip2sm36902413pjb.34.2022.01.04.09.25.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jan 2022 09:25:40 -0800 (PST) Date: Tue, 4 Jan 2022 17:25:37 +0000 From: Sean Christopherson To: Like Xu Cc: Paolo Bonzini , Jim Mattson , Wanpeng Li , Vitaly Kuznetsov , Joerg Roedel , Peter Zijlstra , Like Xu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 01/17] perf/x86/intel: Add EPT-Friendly PEBS for Ice Lake Server Message-ID: References: <20211210133525.46465-1-likexu@tencent.com> <20211210133525.46465-2-likexu@tencent.com> <69ad949e-4788-0f93-46cb-6af6f79a9f24@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69ad949e-4788-0f93-46cb-6af6f79a9f24@gmail.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Dec 31, 2021, Like Xu wrote: > On 31/12/2021 2:13 am, Sean Christopherson wrote: > > On Fri, Dec 10, 2021, Like Xu wrote: > > > The new hardware facility supporting guest PEBS is only available on > > > Intel Ice Lake Server platforms for now. KVM will check this field > > > through perf_get_x86_pmu_capability() instead of hard coding the cpu > > > models in the KVM code. If it is supported, the guest PEBS capability > > > will be exposed to the guest. > > > > So what exactly is this new feature? I've speed read the cover letter and a few > > changelogs and didn't find anything that actually explained when this feature does. > > > > Please check Intel SDM Vol3 18.9.5 for this "EPT-Friendly PEBS" feature. > > I assume when an unfamiliar feature appears in the patch SUBJECT, > the reviewer may search for the exact name in the specification. C'mon, seriously? How the blazes am I supposed to know that the feature name is EPT-Friendly PEBS? Or that it's even in the SDM (it's not in the year-old version of the SDM I currently have open) versus one of the many ISE docs? This is not hard. Please spend the 30 seconds it takes to write a small blurb so that reviewers don't have to spend 5+ minutes wondering WTF this does. Add support for EPT-Friendly PEBS, a new CPU feature that enlightens PEBS to translate guest linear address through EPT, and facilitates handling VM-Exits that occur when accessing PEBS records. More information can be found in the release of Intel's SDM, Volume 3, 18.9.5 "EPT-Friendly PEBS".