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From: Dave Hansen <dave.hansen@intel.com>
To: Guixiong Wei <weiguixiong@bytedance.com>, x86@kernel.org
Cc: Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	"Chang S . Bae" <chang.seok.bae@intel.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] x86/fpu: Free dynamic fpstate on exec()
Date: Tue, 29 Sep 2026 09:53:29 -0700	[thread overview]
Message-ID: <7e945daf-2e1e-468b-8701-db6bbd4ef085@intel.com> (raw)
In-Reply-To: <20260929151013.81562-2-weiguixiong@bytedance.com>

On 9/29/26 08:10, Guixiong Wei wrote:
> Preserve the old fpstate pointer across fpstate_reset() and free it only
> after fpu_reset_fpstate_regs() has invalidated FPU register ownership.
> This ordering prevents a context switch from saving FPU registers through
> a freed fpstate pointer.

Are there any fpstate_reset() paths where this matters?

I mean, the init task, obviously not. It doesn't have a dynamic fpstate.
During exec() this reset happens while:

	bprm->mm = NULL;

among other things, so I really don't think it's even remotely in the
context of getting context-switched to.

For clone(), the destination task is also not in any condition to be
context-switched to.

So why defend against context switching? What am I missing?

      parent reply	other threads:[~2026-09-29 16:54 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-29 15:10 Guixiong Wei
2026-09-29 15:57 ` Dave Hansen
2026-09-29 16:53 ` Dave Hansen [this message]

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