linux-kernel - Re: [PATCH v8 5/6] x86/fpu/xstate: Introduce "guest-only" supervisor xfeature set

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Message-ID: <aDnXJS37+sOtDIrV@AUSJOHALLEN.amd.com>
Date: Fri, 30 May 2025 11:04:53 -0500
From: John Allen <john.allen@....com>
To: Chao Gao <chao.gao@...el.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	tglx@...utronix.de, dave.hansen@...el.com, seanjc@...gle.com,
	pbonzini@...hat.com, peterz@...radead.org,
	rick.p.edgecombe@...el.com, weijiang.yang@...el.com, bp@...en8.de,
	chang.seok.bae@...el.com, xin3.li@...el.com,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Maxim Levitsky <mlevitsk@...hat.com>,
	Mitchell Levy <levymitchell0@...il.com>,
	Vignesh Balasubramanian <vigbalas@....com>
Subject: Re: [PATCH v8 5/6] x86/fpu/xstate: Introduce "guest-only" supervisor
 xfeature set

On Thu, May 22, 2025 at 08:10:08AM -0700, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@...el.com>
> 
> In preparation for upcoming CET virtualization support, the CET supervisor
> state will be added as a "guest-only" feature, since it is required only by
> KVM (i.e., guest FPUs). Establish the infrastructure for "guest-only"
> features.
> 
> Define a new XFEATURE_MASK_GUEST_SUPERVISOR mask to specify features that
> are enabled by default in guest FPUs but not in host FPUs. Specifically,
> for any bit in this set, permission is granted and XSAVE space is allocated
> during vCPU creation. Non-guest FPUs cannot enable guest-only features,
> even dynamically, and no XSAVE space will be allocated for them.
> 
> The mask is currently empty, but this will be changed by a subsequent
> patch.
> 
> Co-developed-by: Chao Gao <chao.gao@...el.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

Reviewed-by: John Allen <john.allen@....com>