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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jae5C-0005ML-1U; Mon, 18 May 2020 11:37:22 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jae59-0005Lu-56 for linux-arm-kernel@lists.infradead.org; Mon, 18 May 2020 11:37:20 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 73515106F; Mon, 18 May 2020 04:37:18 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D9F263F52E; Mon, 18 May 2020 04:37:15 -0700 (PDT) Date: Mon, 18 May 2020 12:37:10 +0100 From: Mark Rutland To: Will Deacon Subject: Re: [PATCH 1/6] arm64: scs: Store absolute SCS stack pointer value in thread_info Message-ID: <20200518113710.GA1957@C02TD0UTHF1T.local> References: <20200515172756.27185-1-will@kernel.org> <20200515172756.27185-2-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200515172756.27185-2-will@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200518_043719_233996_B10887DB X-CRM114-Status: GOOD ( 13.71 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kees Cook , Jann Horn , Peter Zijlstra , Catalin Marinas , linux-kernel@vger.kernel.org, Mark Rutland , Sami Tolvanen , kernel-team@android.com, Ard Biesheuvel , 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 Fri, May 15, 2020 at 06:27:51PM +0100, Will Deacon wrote: > Storing the SCS information in thread_info as a {base,offset} pair > introduces an additional load instruction on the ret-to-user path, > since the SCS stack pointer in x18 has to be converted back to an offset > by subtracting the base. > > Replace the offset with the absolute SCS stack pointer value instead > and avoid the redundant load. > > Signed-off-by: Will Deacon One trivial nit below, but regardless this looks sound to me, and I certainly prefer having the absolute address rather than an offset, so: Reviewed-by: Mark Rutland > diff --git a/kernel/scs.c b/kernel/scs.c > index 9389c28f0853..5ff8663e4a67 100644 > --- a/kernel/scs.c > +++ b/kernel/scs.c > @@ -60,8 +60,7 @@ int scs_prepare(struct task_struct *tsk, int node) > if (!s) > return -ENOMEM; > > - task_scs(tsk) = s; > - task_scs_offset(tsk) = 0; > + task_scs(tsk) = task_scs_sp(tsk) = s; I think this would be more legible as two statements: | task_sys(tsk) = s; | task_scs_sp(tsk) = s; ... as we usually save `foo = bar = baz` stuff for the start of a function or within loop conditions. Thanks, Mark. > scs_account(tsk, 1); > return 0; > } > -- > 2.26.2.761.g0e0b3e54be-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel