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Date:   Thu, 19 Oct 2023 11:07:33 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Uros Bizjak <ubizjak@gmail.com>, Nadav Amit <namit@vmware.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()
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On Wed, Oct 18, 2023 at 03:40:05PM -0700, Linus Torvalds wrote:
> On Wed, 18 Oct 2023 at 14:40, Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > The ones in "raw" form are not IRQ safe and these are implemented
> > without volatile qualifier.
> 
> You are misreading it.
> 
> Both *are* irq safe - on x86.

Stronger, x86 arch code very much relies on them being NMI-safe. Which
makes the generic implementation insufficient. 

They *must* be single RmW instructions on x86.