From nobody Fri Dec 19 07:02:13 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1772C7EE24 for ; Sat, 3 Jun 2023 20:09:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231252AbjFCUJE (ORCPT ); Sat, 3 Jun 2023 16:09:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231628AbjFCUIp (ORCPT ); Sat, 3 Jun 2023 16:08:45 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BCACFE60 for ; Sat, 3 Jun 2023 13:07:53 -0700 (PDT) Message-ID: <20230603200459.775471968@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1685822820; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=fh2uTBEHG28Fh31y7f2tmR7yGLyMLoAyt+FF1TixMCg=; b=1nVnHokyojIXwrcsLwEvNrRA4MA/Gp4A/mBpI6uAEV1v/jCxYGSnkpIOK13V1qC9G1cZ68 E0Wt+8KqnQK18DnJRPKdRxwf91S4QA5Y42Tq1WmTqsOF/yqIlLllKO5pQ4bFhhY3wTqQgr 4Px0WvA8jO3bRnsrseb5mKoj67Vo4TPrNsdaa7Dwj1VLeq0KvQPdBOCvei4ulO0CvRwoue 5bdcxZywog18NE2kVcZJv5vK/CVo4mGvrgvPcQdw786B/16F0MRU9jxZ0PFOlLKF711UiT vLQs43veq6Pkof2vLWl6tpJjJYljK/tnGppsn6lnxiP2WWUF4zrYmoP5GdpuUQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1685822820; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=fh2uTBEHG28Fh31y7f2tmR7yGLyMLoAyt+FF1TixMCg=; b=ZYmnES9mtLf+uuLZaMIpIFu5yZDJIJKyATWf0PD4/i7pu+IKi4nksO4gNyQ6S9IsqkhH1t YllL+o1xr/zXinCg== From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Ashok Raj , Dave Hansen , Tony Luck , Arjan van de Veen , Peter Zijlstra , Eric Biederman Subject: [patch 3/6] x86/smp: Use dedicated cache-line for mwait_play_dead() References: <20230603193439.502645149@linutronix.de> MIME-Version: 1.0 Date: Sat, 3 Jun 2023 22:07:00 +0200 (CEST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Monitoring idletask::thread_info::flags in mwait_play_dead() has been an obvious choice as all what is needed is a cache line which is not written by other CPUs. But there is a use case where a "dead" CPU needs to be brought out of that mwait(): kexec(). The CPU needs to be brought out of mwait before kexec() as kexec() can overwrite text, pagetables, stacks and the monitored cacheline of the original kernel. The latter causes mwait to resume execution which obviously causes havoc on the kexec kernel which results usually in triple faults. Use a dedicated per CPU storage to prepare for that. Signed-off-by: Thomas Gleixner --- arch/x86/kernel/smpboot.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -101,6 +101,17 @@ EXPORT_PER_CPU_SYMBOL(cpu_die_map); DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info); EXPORT_PER_CPU_SYMBOL(cpu_info); =20 +struct mwait_cpu_dead { + unsigned int control; + unsigned int status; +}; + +/* + * Cache line aligned data for mwait_play_dead(). Separate on purpose so + * that it's unlikely to be touched by other CPUs. + */ +static DEFINE_PER_CPU_ALIGNED(struct mwait_cpu_dead, mwait_cpu_dead); + /* Logical package management. We might want to allocate that dynamically = */ unsigned int __max_logical_packages __read_mostly; EXPORT_SYMBOL(__max_logical_packages); @@ -1758,10 +1769,10 @@ EXPORT_SYMBOL_GPL(cond_wakeup_cpu0); */ static inline void mwait_play_dead(void) { + struct mwait_cpu_dead *md =3D this_cpu_ptr(&mwait_cpu_dead); unsigned int eax, ebx, ecx, edx; unsigned int highest_cstate =3D 0; unsigned int highest_subcstate =3D 0; - void *mwait_ptr; int i; =20 if (boot_cpu_data.x86_vendor =3D=3D X86_VENDOR_AMD || @@ -1796,13 +1807,6 @@ static inline void mwait_play_dead(void) (highest_subcstate - 1); } =20 - /* - * This should be a memory location in a cache line which is - * unlikely to be touched by other processors. The actual - * content is immaterial as it is not actually modified in any way. - */ - mwait_ptr =3D ¤t_thread_info()->flags; - wbinvd(); =20 while (1) { @@ -1814,9 +1818,9 @@ static inline void mwait_play_dead(void) * case where we return around the loop. */ mb(); - clflush(mwait_ptr); + clflush(md); mb(); - __monitor(mwait_ptr, 0, 0); + __monitor(md, 0, 0); mb(); __mwait(eax, 0);