From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751906AbbIQRHM (ORCPT ); Thu, 17 Sep 2015 13:07:12 -0400 Received: from foss.arm.com ([217.140.101.70]:42565 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751663AbbIQRHK (ORCPT ); Thu, 17 Sep 2015 13:07:10 -0400 Date: Thu, 17 Sep 2015 18:07:05 +0100 From: Catalin Marinas To: Jungseok Lee Cc: James Morse , Mark Rutland , Will Deacon , "linux-kernel@vger.kernel.org" , "takahiro.akashi@linaro.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v2] arm64: Introduce IRQ stack Message-ID: <20150917170705.GQ25444@e104818-lin.cambridge.arm.com> References: <1442155337-7020-1-git-send-email-jungseoklee85@gmail.com> <20150916112520.GH28771@arm.com> <55FA9708.5070200@arm.com> <8C4599C6-E5F8-4527-AAFF-9FEF295526BB@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8C4599C6-E5F8-4527-AAFF-9FEF295526BB@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 17, 2015 at 09:36:04PM +0900, Jungseok Lee wrote: > On Sep 17, 2015, at 7:33 PM, James Morse wrote: > > On 16/09/15 12:25, Will Deacon wrote: > >> On Sun, Sep 13, 2015 at 03:42:17PM +0100, Jungseok Lee wrote: > >>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h > >>> index dcd06d1..44839c0 100644 > >>> --- a/arch/arm64/include/asm/thread_info.h > >>> +++ b/arch/arm64/include/asm/thread_info.h > >>> @@ -73,8 +73,11 @@ static inline struct thread_info *current_thread_info(void) __attribute_const__; > >>> > >>> static inline struct thread_info *current_thread_info(void) > >>> { > >>> - return (struct thread_info *) > >>> - (current_stack_pointer & ~(THREAD_SIZE - 1)); > >>> + unsigned long sp_el0; > >>> + > >>> + asm volatile("mrs %0, sp_el0" : "=r" (sp_el0)); > >>> + > >>> + return (struct thread_info *)(sp_el0 & ~(THREAD_SIZE - 1)); > >> > >> This looks like it will generate worse code than our current implementation, > >> thanks to the asm volatile. Maybe just add something like a global > >> current_stack_pointer_el0? [...] > --- a/arch/arm64/include/asm/thread_info.h > +++ b/arch/arm64/include/asm/thread_info.h > @@ -77,7 +77,7 @@ static inline struct thread_info *current_thread_info(void) > > asm volatile("mrs %0, sp_el0" : "=r" (sp_el0)); > > - return (struct thread_info *)(sp_el0 & ~(THREAD_SIZE - 1)); > + return (struct thread_info *)sp_el0; > } This makes sense, since we just use sp_el0 as a scratch register, store the current thread_info address directly. But, as James mentioned, I don't think you need asm volatile, just asm (it has a small impact in my tests). -- Catalin