linux-kernel - Re: arm64: pseudo NMI bootconfig question

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Message-ID: <aRW68JGA4xBGxjbs@willie-the-truck>
Date: Thu, 13 Nov 2025 11:03:12 +0000
From: Will Deacon <will@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Marc Zyngier <maz@...nel.org>, catalin.marinas@....com,
	mark.rutland@....com, paulmck@...nel.org, mhiramat@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: arm64: pseudo NMI bootconfig question

On Thu, Nov 13, 2025 at 01:36:48AM -0800, Breno Leitao wrote:
> Helo Marc,
> 
> On Wed, Nov 12, 2025 at 02:21:22PM +0000, Marc Zyngier wrote:
> > On Wed, 12 Nov 2025 14:05:43 +0000,
> > Breno Leitao <leitao@...ian.org> wrote:
> ...
> > > Question:
> > > 
> > > Would it make sense to provide an option to enable pseudo NMI in certain
> > > kernel configuration without requiring an extra command-line parameter?
> > 
> > [I wasn't asked, but I'll give my answer anyway]
> > 
> > The short answer is no. The long answer is that there is so much
> > broken HW out there that dies a painful death when enabling pseudo-NMI
> > that is isn't practical to do so.
> 
> That’s helpful to know. I hadn’t realized there were potential issues
> with hardware implementation, which explains why it isn’t
> straightforward to enable. Thanks for the additional context.

FWIW, I've also run into platforms where the _hardware_ is fine but the
TZ integration can't handle Linux using priority masking properly.

Will