linux-kernel - Re: [EXTERNAL] [PATCH AUTOSEL 6.4 02/15] x86/smpboot: Implement a bit spinlock to protect the realmode stack

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Message-ID: <937d902965db22fa54668c985a09dc4c07dbb0b1.camel@infradead.org>
Date:   Mon, 03 Jul 2023 10:19:23 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Helge Deller <deller@....de>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        usama.arif@...edance.com, brgerst@...il.com, jgross@...e.com,
        jpoimboe@...nel.org, thomas.lendacky@....com
Subject: Re: [EXTERNAL] [PATCH AUTOSEL 6.4 02/15] x86/smpboot: Implement a
 bit spinlock to protect the realmode stack

On Sun, 2023-07-02 at 15:40 -0400, Sasha Levin wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> [ Upstream commit f6f1ae9128d2a080ecdd55f85e8a0ca3ed1d58eb ]
> 
> Parallel AP bringup requires that the APs can run fully parallel through
> the early startup code including the real mode trampoline.
> 
> To prepare for this implement a bit-spinlock to serialize access to the
> real mode stack so that parallel upcoming APs are not going to corrupt each
> others stack while going through the real mode startup code.

This is also preparation for the parallel CPU bringup and (again,
unless I'm missing something) doesn't need to be backported to stable.

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