linux-kernel - Re: [PATCH v5 0/7] Introduce CET supervisor state support

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Message-ID: <0f43a0e3e6b839779a36c0474a7ccd85ac753ba3.camel@intel.com>
Date: Thu, 24 Apr 2025 23:28:33 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Gao, Chao" <chao.gao@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>
CC: "ebiggers@...gle.com" <ebiggers@...gle.com>, "Bae, Chang Seok"
	<chang.seok.bae@...el.com>, "Spassov, Stanislav" <stanspas@...zon.de>,
	"levymitchell0@...il.com" <levymitchell0@...il.com>,
	"samuel.holland@...ive.com" <samuel.holland@...ive.com>, "Li, Xin3"
	<xin3.li@...el.com>, "Yang, Weijiang" <weijiang.yang@...el.com>,
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	<aruna.ramakrishna@...cle.com>, "bp@...en8.de" <bp@...en8.de>, "Liu, Zhao1"
	<zhao1.liu@...el.com>, "ubizjak@...il.com" <ubizjak@...il.com>
Subject: Re: [PATCH v5 0/7] Introduce CET supervisor state support

On Thu, 2025-04-10 at 15:24 +0800, Chao Gao wrote:
> == Performance ==
> 
> We measured context-switching performance with the benchmark [4] in following
> three cases.
> 
> case 1: the baseline. i.e., this series isn't applied
> case 2: baseline + this series. CET-S space is allocated for guest fpu only.
> case 3: baseline + allocate CET-S space for all tasks. Hardware init
>         optimization avoids writing out CET-S space on each XSAVES.
> 
> The performance differences in the three cases are very small and fall within the
> run-to-run variation.

It seems like this dilemma is settled.

I had the question about why we need a separate guest user features and size.
Otherwise it looks pretty good to me. I'll return to review the rest after the
answer for the need for separate guest default user features.