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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtvjO-0001MW-Bw; Wed, 13 Feb 2019 14:41:47 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2307C20D0C1E6; Wed, 13 Feb 2019 15:41:45 +0100 (CET) Date: Wed, 13 Feb 2019 15:41:45 +0100 From: Peter Zijlstra To: Julien Thierry Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Message-ID: <20190213144145.GY32494@hirez.programming.kicks-ass.net> References: <1547560709-56207-4-git-send-email-julien.thierry@arm.com> <20190211134527.GA121589@gmail.com> <20190211135159.GC32511@hirez.programming.kicks-ass.net> <20190213103553.GO32494@hirez.programming.kicks-ass.net> <1c2429a4-9df9-40a3-98e0-51577de4bd6a@arm.com> <20190213131720.GU32494@hirez.programming.kicks-ass.net> <20190213140025.GB6346@brain-police> <20190213142524.GW32494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: catalin.marinas@arm.com, Will Deacon , linux-kernel@vger.kernel.org, valentin.schneider@arm.com, mingo@redhat.com, james.morse@arm.com, hpa@zytor.com, Ingo Molnar , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Feb 13, 2019 at 02:39:22PM +0000, Julien Thierry wrote: > Hi Peter, > > On 13/02/2019 14:25, Peter Zijlstra wrote: > > On Wed, Feb 13, 2019 at 02:00:26PM +0000, Will Deacon wrote: > >> The difference is because getting preempted in the sequence above is > >> triggered off the back of an interrupt. On arm64, and I think also on x86, > >> the user access state (SMAP or PAN) is saved and restored across exceptions > >> but not across context switch. > > > > A quick reading of the SDM seems to suggest the SMAP state is part of > > EFLAGS, which is context switched just fine AFAIK. > > > I fail to see where this is happening when looking at the switch_to() > logic in x86_64. Yeah, me too.. we obviously preserve EFLAGS for user context, but for kernel-kernel switches we do not seem to preserve it :-( _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel