From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C4DC71487F6 for ; Sun, 6 Apr 2025 17:21:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743960100; cv=none; b=MLnsoAIEW+MGpcVEG2wowkIDnCNf8ifMbMhg1Cg66FPoj1IQKM9sAtGXfRN5q7DTqvKxATODe4m+yDXyw6/6N1whspn9g5C1XpIHWyUaaHTJJWF0Gs2xZghVFj0EsxFWcqV/BObzqnd6B0ADLxtl6r27qOHCttNCzYk7cY29U3E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743960100; c=relaxed/simple; bh=TLDCz0ijceRvrDZBjTDRhs68DEmOTUvRPjZfCHwJkCA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NppqbnY/fyffM5cX8MuO7OcUcqN6k7mgd1C8VL5/QT6BhvXgiUNlR9Edt9gYxtD5bsOWTPoHQ7ew7sOPxnu6SC8wp4riJCxvd+rpSZl9ssy/TsYMN7voOFOHt5vzusXeh6FX2J7sF0qlcbtB0CHjqsxu+W0ep8XXjg5VToh7j+Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=t7VGGs2l; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="t7VGGs2l" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F753C4CEE3; Sun, 6 Apr 2025 17:21:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743960100; bh=TLDCz0ijceRvrDZBjTDRhs68DEmOTUvRPjZfCHwJkCA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=t7VGGs2lsugmRJa1bU+IT59OkXpCFEw/PjL0KmVWbedYwWHPw6UwMuPY2Y59KW7tx W4qd9OyxB+hXvfTVbTE7rQThNkJqEH5YvNTdUwCYMxXUM0pcnoBG3FsLNT3rLv41mx sE+/6aBipGHZJh+CoxruDBy69jReoe5Vr9k0uuq7fFKKRpbmPKqZemiv0qFvx2EcVt 6Ud6P93lDkzCn08/sMxNiwyAfGkyYg792avQba340dGV78WSNeTKrWyX/MJmAcQaj6 aI86YDZRLrfyytdm7qVKiMsVa/NDXjuINXOcyqolOV/mcywcIQmNTHHZyCFO6v9UyX XYxC/ztLmAzFA== Date: Sun, 6 Apr 2025 19:21:35 +0200 From: Ingo Molnar To: Uros Bizjak Cc: Andrew Cooper , LKML , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" Subject: Re: [PATCH v2] x86/idle: Remove MFENCEs for X86_BUG_CLFLUSH_MONITOR Message-ID: References: <20250402172458.1378112-1-andrew.cooper3@citrix.com> <1640cf43-8125-a562-91f9-9b306b863dc7@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1640cf43-8125-a562-91f9-9b306b863dc7@gmail.com> * Uros Bizjak wrote: > There is another instance of the same sequence in arch/x86/kernel/smpboot.c: > > /* > * The CLFLUSH is a workaround for erratum AAI65 for > * the Xeon 7400 series. It's not clear it is actually > * needed, but it should be harmless in either case. > * The WBINVD is insufficient due to the spurious-wakeup > * case where we return around the loop. > */ > mb(); > clflush(md); > mb(); > __monitor(md, 0, 0); > mb(); > __mwait(eax_hint, 0); True, but I wouldn't touch that - the shutdown path is not a performance critical code path in any fashion, and it's often difficult to debug on real hardware, so the cost/benefit factor is abnormally high. Thanks, Ingo