From mboxrd@z Thu Jan 1 00:00:00 1970 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8A365C433EF for ; Fri, 10 Dec 2021 12:07:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=jmsPk4/mnYn3il59EiqPKxvG3LywR080D43KKXfddpw=; b=3bwP3VaPeJbupb Kl11qQ/M8/Fi/COmX6hMYF1QgVgv9DUnj+TIDpEYEEDDeaKaXGtZ2PjsKKuifwqFPuqb6/Wi8bdw9 ilD4QpgdCJL2C/YH6amln88kZO6TLAf0ntiU3thJ+bEj59a/GU4LJOEzfPH1KxasZeEYic/Nfp137 Lmb7J+H299vsSkLXJ9vyLMNmaj7Ft6yvZ2IDp5psYBMFRiLeZVw9q8ngaKRzwy/UrSjy59k5OuHS3 k4MTtHt7pzJqz+Ox+2gwBZ49MF6EsvH3D0rcXX1X8a2aNNIGRmEWcuu2XrH7HU7jhcOaqIFnOg5Y3 tjO25tAbD6b9TjID29mg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvefN-001mNy-HD; Fri, 10 Dec 2021 12:06:21 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvefJ-001mNK-L0 for linux-arm-kernel@lists.infradead.org; Fri, 10 Dec 2021 12:06:19 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 4B570B8275E; Fri, 10 Dec 2021 12:06:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A4C85C00446; Fri, 10 Dec 2021 12:06:13 +0000 (UTC) Date: Fri, 10 Dec 2021 12:06:10 +0000 From: Catalin Marinas To: Peter Collingbourne Cc: Vincenzo Frascino , Will Deacon , Andrey Konovalov , Mark Rutland , Evgenii Stepanov , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arm64: mte: avoid clearing PSTATE.TCO on entry unless necessary Message-ID: References: <20211110220735.3937127-1-pcc@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211110220735.3937127-1-pcc@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211210_040617_853822_2CF097B2 X-CRM114-Status: GOOD ( 18.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 10, 2021 at 02:07:35PM -0800, Peter Collingbourne wrote: > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 2f69ae43941d..a78ec15f5bbc 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -189,6 +189,27 @@ alternative_cb_end > #endif > .endm > > + .macro mte_clear_tco, sctlr > + /* > + * Re-enable tag checking (TCO set on exception entry). This is only > + * necessary if MTE is enabled in either the kernel or the userspace > + * task in synchronous mode. With MTE disabled in the kernel and > + * disabled or asynchronous in userspace, tag check faults (including in > + * uaccesses) are not reported, therefore there is no need to re-enable > + * checking. This is beneficial on microarchitectures where re-enabling > + * TCO is expensive. > + */ > +#ifdef CONFIG_ARM64_MTE > +alternative_cb kasan_hw_tags_enable > + tbz \sctlr, #SCTLR_EL1_TCF0_SHIFT, 1f > +alternative_cb_end > +alternative_if ARM64_MTE > + SET_PSTATE_TCO(0) > +alternative_else_nop_endif > +1: > +#endif > + .endm The patch looks fine to me but I recall in a private conversation with Mark he proposed the idea of moving this to entry-common.c (unless it was about something completely different). The downside is that we run with the TCO set for slightly longer. There shouldn't be a major drawback currently as we don't have stack tagging anyway. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel