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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B39EFC52D6F for ; Wed, 21 Aug 2024 08:50:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1F4796B00E3; Wed, 21 Aug 2024 04:50:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1A6346B00E4; Wed, 21 Aug 2024 04:50:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 06BEC6B00E5; Wed, 21 Aug 2024 04:50:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id DD9C56B00E3 for ; Wed, 21 Aug 2024 04:50:33 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 8FF0340A87 for ; Wed, 21 Aug 2024 08:50:33 +0000 (UTC) X-FDA: 82475631546.15.7BC08CB Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf11.hostedemail.com (Postfix) with ESMTP id E5FCC4000C for ; Wed, 21 Aug 2024 08:50:31 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=none; spf=pass (imf11.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1724230191; a=rsa-sha256; cv=none; b=SULi9TePcoRjonLdWpgOvAiOAiH8Y98Cs7I3PdnqBQc4MK5dOPUEJSf5y00HDZhl3mqfDE 9EK2fNuS9WmRjR3rXV1fD29cW/B0trc5IctJ3qTdDTimpig4ct6h4UNNnYCEda+9blwMRz bCuuzujJKxltHp95LqUIB29IHCEMC2s= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; spf=pass (imf11.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1724230191; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rTMw7j6JrVUZ6p7Us+X4r+JabCgEHQgh2cZwzSHJvf0=; b=Zz5GNZ8/+poSYl9OQoR2LvZmyZj5O/pPHBdBwQSog1rFS/8WDC/J8tfiHBInsrftKml5Yt 2Qv1Lf1058eTFhof/LW2amq5OyzPCZOt5ohXs+unOwpbrNBqlYGlRURADeVK/cKbcmPM/0 rcExQxTfNOcytUvT2jCSSrXBTTq323Q= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id CE55960F57; Wed, 21 Aug 2024 08:50:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F403AC32782; Wed, 21 Aug 2024 08:50:24 +0000 (UTC) Date: Wed, 21 Aug 2024 09:50:22 +0100 From: Catalin Marinas To: Mark Brown Cc: Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Thiago Jung Bauermann , Ross Burton , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v10 19/40] arm64/gcs: Context switch GCS state for EL0 Message-ID: References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org> <20240801-arm64-gcs-v10-19-699e2bd2190b@kernel.org> <0f6fd3ec-2481-4507-af0e-3cbbb7406b54@sirena.org.uk> <3b316422-7f88-4f5d-a691-eb9209ec4ba9@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3b316422-7f88-4f5d-a691-eb9209ec4ba9@sirena.org.uk> X-Stat-Signature: tp5gyuynii7wp8y7tz19tbb98q69f3zq X-Rspamd-Queue-Id: E5FCC4000C X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1724230231-897596 X-HE-Meta: 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 NmZRGQMj 7fo2/HTTVR55KWuWAkqaSyoMgjn0nO8+bQwqiRYmSoZLWdM6CRGYWWDtsdiT+o+ttAS970DuzUHQD0/JmvTqpcG7By97Qv2fyZppG4+R1AMlxM/etXbS0MhSxSxkqgqTe2kJJbM4Yrnf3lLF6qMCg+69JnqI0HxTa8irc2+pn0ZX9aXfhqHKCl44gneCYLlsO+onbba3JYCe6SNX2Rz5vO5WKU4VVtCR2JQvXeZFl752Zma5aWOsdFuySRDHlhAZHXjnDoC6Q7vX8jItbJu8mQPmaHaJ43hcrNRJugTLMBrEjiRJk+sdCAcNKxpHtMSMofsY1XZyCUGR48ou1WPrcKYe15JUvbxoWW3qCL1GLP25pk7xGc8aLO6BTmdiwcwwGlQb+rQz4VBJZkCsxjBtzSwfuRVf2UJx3OPDv6YuMksyk2fo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 20, 2024 at 06:56:19PM +0100, Mark Brown wrote: > On Mon, Aug 19, 2024 at 04:44:52PM +0100, Mark Brown wrote: > > On Mon, Aug 19, 2024 at 12:46:13PM +0100, Catalin Marinas wrote: > > > On Thu, Aug 01, 2024 at 01:06:46PM +0100, Mark Brown wrote: > > > > > + /* > > > > + * Ensure that GCS changes are observable by/from other PEs in > > > > + * case of migration. > > > > + */ > > > > + if (task_gcs_el0_enabled(current) || task_gcs_el0_enabled(next)) > > > > + gcsb_dsync(); > > > > Could we do the sysreg writing under this 'if' block? If no app is using > > > GCS (which would be the case for a while), it looks like unnecessary > > > sysreg accesses. > > > Yes, that should be fine I think. > > I forgot when writing the above that we always allow reads from > GCSPR_EL0 in order to avoid corner cases for unwinders in the case of > asynchronous disable. I'd expect that to be cheap to access though. But then gcs_preserve_current_state() doesn't save the GCSPR_EL0 value if the shadow stack was disabled. At the subsequent switch to this task, we write some stale value. -- Catalin