linux-kernel - Re: [RFC PATCH 7/7] arm64/efi: Call EFI runtime services without disabling preemption

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Message-ID: <CAMj1kXEw=RSnf_Af=+AKWmuxJ+0dL_4CFSX7TyKo+SSKpxc6Bw@mail.gmail.com>
Date: Tue, 15 Jul 2025 10:46:43 +1000
From: Ard Biesheuvel <ardb@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [RFC PATCH 7/7] arm64/efi: Call EFI runtime services without
 disabling preemption

On Mon, 14 Jul 2025 at 20:55, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Jul 14, 2025 at 12:20:30PM +1000, Ard Biesheuvel wrote:
> > On Fri, 11 Jul 2025 at 23:48, Peter Zijlstra <peterz@...radead.org> wrote:
...
> > > Is the migrate_disable() strictly required, or just paranoia?
> > >
> >
> > Runtime services might be polling the secure firmware for an async
> > completion when they are interrupted, and so I don't think it is
> > generally safe to assume that an interrupted EFI runtime service can
> > be resumed on another CPU.
>
> Can we please get a comment with that migrate_disable() explaining this?
>

Sure