linux-kernel - Re: [PATCH v8 2/6] x86/fpu: Initialize guest FPU permissions from guest defaults

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Message-ID: <aDjOJ4tQAmHwBiXg@AUSJOHALLEN.amd.com>
Date: Thu, 29 May 2025 16:14:15 -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>,
	Stanislav Spassov <stanspas@...zon.de>,
	Eric Biggers <ebiggers@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v8 2/6] x86/fpu: Initialize guest FPU permissions from
 guest defaults

On Thu, May 22, 2025 at 08:10:05AM -0700, Chao Gao wrote:
> Currently, fpu->guest_perm is copied from fpu->perm, which is derived from
> fpu_kernel_cfg.default_features.
> 
> Guest defaults were introduced to differentiate the features and sizes of
> host and guest FPUs. Copying guest FPU permissions from the host will lead
> to inconsistencies between the guest default features and permissions.
> 
> Initialize guest FPU permissions from guest defaults instead of host
> defaults. This ensures that any changes to guest default features are
> automatically reflected in guest permissions, which in turn guarantees
> that fpstate_realloc() allocates a correctly sized XSAVE buffer for guest
> FPUs.
> 
> Suggested-by: Chang S. Bae <chang.seok.bae@...el.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

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