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Date:   Tue, 9 May 2023 15:57:49 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        David Woodhouse <dwmw2@infradead.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Brian Gerst <brgerst@gmail.com>,
        Arjan van de Veen <arjan@linux.intel.com>,
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        Tom Lendacky <thomas.lendacky@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Paul Menzel <pmenzel@molgen.mpg.de>,
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        Piotr Gorski <lucjan.lucjanov@gmail.com>,
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        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
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        Sabin Rapan <sabrapan@amazon.com>,
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        David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [patch v3 35/36] x86/smpboot: Support parallel startup of
 secondary CPUs
Message-ID: <20230509135749.GB83892@hirez.programming.kicks-ass.net>
References: <20230508181633.089804905@linutronix.de>
 <20230508185219.176824543@linutronix.de>
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On Mon, May 08, 2023 at 09:44:23PM +0200, Thomas Gleixner wrote:
> +	/*  APIC ID not found in the table. Drop the trampoline lock and bail. */
> +	movq	trampoline_lock(%rip), %rax

Again:

	movl	$0, (%rax)

is sufficient for unlock.

> +	lock
> +	btrl	$0, (%rax)