linux-kernel - Re: [Patch v6 08/22] x86/fpu: Ensure TIF_NEED_FPU

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Message-ID: <5c3ea318-4543-42a4-9b81-7a1da0b8bed1@intel.com>
Date: Wed, 11 Feb 2026 11:39:45 -0800
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>, Peter Zijlstra
	<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Arnaldo Carvalho de
 Melo" <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Thomas Gleixner
	<tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Ian Rogers
	<irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Jiri Olsa
	<jolsa@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>, Eranian Stephane <eranian@...gle.com>
CC: Mark Rutland <mark.rutland@....com>, <broonie@...nel.org>, Ravi Bangoria
	<ravi.bangoria@....com>, <linux-kernel@...r.kernel.org>,
	<linux-perf-users@...r.kernel.org>, Zide Chen <zide.chen@...el.com>, "Falcon
 Thomas" <thomas.falcon@...el.com>, Dapeng Mi <dapeng1.mi@...el.com>, "Xudong
 Hao" <xudong.hao@...el.com>
Subject: Re: [Patch v6 08/22] x86/fpu: Ensure TIF_NEED_FPU_LOAD is set after
 saving FPU state

On 2/8/2026 11:20 PM, Dapeng Mi wrote:
> Ensure that the TIF_NEED_FPU_LOAD flag is always set after saving the
> FPU state. This guarantees that the user space FPU state has been saved
> whenever the TIF_NEED_FPU_LOAD flag is set.
> 
> A subsequent patch will verify if the user space FPU state can be
> retrieved from the saved task FPU state in the NMI context by checking
> the TIF_NEED_FPU_LOAD flag.
> 
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>

I could check some previous discussions there:
https://lore.kernel.org/all/20251204151735.GO2528459@noisy.programming.kicks-ass.net/

With that, I think I can get the context of this change -- tightening 
the flag up with the buffer against *NMIs*.

But the changelog doesn't look clear enough to explain the reason to me.

At least, I guess Links to the past discussions provides better context 
to readers.