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 6B0C5C531DC for ; Fri, 23 Aug 2024 17:10:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ln8zCAp2BKtK4D9ABYeu9MpiwqvQQYwtrKiCWQN+Q4w=; b=FT7DYhRTXMa6D31huQ+OAb4ZUg p0MwuF2yZYxEniW51GlZ+jmVelb8VfRaiIJBIP95yj7yIgBeO2NMPt4MCaD7xLipFhaFrvc997uE+ OdkLQBat6Sq4M8khdyTHCg4d80hUVNwghzR0ZCGF4TExwZBM3FeUc0n7npAC4HMsuPvLvXrotX6i6 K73+1m5zggJ0v3wwdU6HPoD4KyCMterLdPZxk1r8+JfMkbvMisYnWEeFdGdaK5Z0t1VSecwDnzpEO mQecskpx83yO8AhpoOOXYKCH/AS9sPWQYfRPAqgLqPz6sIaLksc30wWVrb8RgH7r08TnNbu6FrxWX sjQbmAjQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1shXnZ-000000005Oe-2k80; Fri, 23 Aug 2024 17:10:05 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1shXmH-000000005EE-1B89 for linux-arm-kernel@lists.infradead.org; Fri, 23 Aug 2024 17:08:46 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 7646860B54; Fri, 23 Aug 2024 17:08:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D713C32786; Fri, 23 Aug 2024 17:08:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724432924; bh=RihPOGh9p93UyuuiwT2FCbCPYyy1oUyaWOUKpt8j+K4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fMDDMyCOPVaR0lNY9h3NbsHg2Bdt69cwbY79/e6UXmXBU5kM9OfPR8wvBL7llF20P 4DAQH9IlKKaP662nLGdhQeBT15sTV8EuWxAkbewdCzRnX7moXjhl60oy28w6PIN1up M7u16xXP7PxQzHcK6CmgYx/mbU0XxD2Rr9ABpZeQk193rmnHV78uERlqK0Pf1QkoFl 9rgDnGWcKdC7M8DMgdfRQxN/+zEZ6xOhtnKDPlPHghDbwwXH6FqIsjlhqeTEBYFNKC WIyQSGTSRuHjVeYzUziQ0SMR09W61Qn6ZfAQfwsVYOzqdgMYpfHJLnU3hc/S0GKZCX AgsBhEuIYFm/A== Date: Fri, 23 Aug 2024 18:08:36 +0100 From: Will Deacon To: Catalin Marinas Cc: Joey Gouly , linux-arm-kernel@lists.infradead.org, nd@arm.com, akpm@linux-foundation.org, aneesh.kumar@kernel.org, aneesh.kumar@linux.ibm.com, anshuman.khandual@arm.com, bp@alien8.de, broonie@kernel.org, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, hpa@zytor.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, naveen.n.rao@linux.ibm.com, npiggin@gmail.com, oliver.upton@linux.dev, shuah@kernel.org, skhan@linuxfoundation.org, szabolcs.nagy@arm.com, tglx@linutronix.de, x86@kernel.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 06/30] arm64: context switch POR_EL0 register Message-ID: <20240823170835.GA1181@willie-the-truck> References: <20240822151113.1479789-1-joey.gouly@arm.com> <20240822151113.1479789-7-joey.gouly@arm.com> <20240823144531.GH32156@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240823_100845_409582_159F8E70 X-CRM114-Status: GOOD ( 16.44 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Aug 23, 2024 at 05:41:06PM +0100, Catalin Marinas wrote: > On Fri, Aug 23, 2024 at 03:45:32PM +0100, Will Deacon wrote: > > On Thu, Aug 22, 2024 at 04:10:49PM +0100, Joey Gouly wrote: > > > +static void permission_overlay_switch(struct task_struct *next) > > > +{ > > > + if (!system_supports_poe()) > > > + return; > > > + > > > + current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0); > > > + if (current->thread.por_el0 != next->thread.por_el0) { > > > + write_sysreg_s(next->thread.por_el0, SYS_POR_EL0); > > > + /* ISB required for kernel uaccess routines when chaning POR_EL0 */ > > > > nit: typo "chaning". > > > > But more substantially, is this just to prevent spurious faults in the > > context of a new thread using a stale value for POR_EL0? > > Not just prevent faults but enforce the permissions from the new > thread's POR_EL0. The kernel may continue with a uaccess routine from > here, we can't tell. Hmm, I wondered if that was the case. It's a bit weird though, because: - There's a window between switch_mm() and switch_to() where you might reasonably expect to be able to execute uaccess routines - kthread_use_mm() doesn't/can't look at this at all - GUP obviously doesn't care So what do we actually gain by having the uaccess routines honour this? Will