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Date: Sun, 18 May 2025 08:34:25 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	linux-crypto@vger.kernel.org, linux-pm@vger.kernel.org,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ayush Jain <Ayush.Jain3@amd.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH 3/3] x86/fpu: Don't support kernel-mode FPU when
 irqs_disabled()
Message-ID: <aCl_cSO2XqtSQEZT@gmail.com>
References: <20250516231858.27899-1-ebiggers@kernel.org>
 <20250516231858.27899-4-ebiggers@kernel.org>
 <aCg2DSYp0nakwX3l@gmail.com>
 <20250517183919.GC1239@sol>
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* Eric Biggers <ebiggers@kernel.org> wrote:

> > Alternatively we could set in_kernel_fpu during CPU bootstrap, and 
> > clear it once we know the FPU is usable? This is only a relatively 
> > short early boot period, with no scheduling, right?
> 
> Yes, if there isn't agreement on this approach we can do that 
> instead.  Say:
> 
> - Replace in_kernel_fpu with kernel_fpu_supported, with the opposite 
>   meaning (so that the initial value of false means "unsupported")

I'm not against simplifying the x86 FPU model to exclude IRQs-off
context (especially if it also micro-optimizes some of the key runtime
kernel-FPU primitives), but it has to be a full solution and we'll have
to see how complicated the EFI changes get.

Ie. without seeing the full cost-benefit balance it's hard to call this
in advance. Mind sending a full series that addresses the EFI case too?

Thanks,

	Ingo