From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965121AbaE2RxI (ORCPT ); Thu, 29 May 2014 13:53:08 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:46399 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964972AbaE2RxF (ORCPT ); Thu, 29 May 2014 13:53:05 -0400 Date: Thu, 29 May 2014 18:52:36 +0100 From: Will Deacon To: Larry Bassel Cc: Catalin Marinas , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linaro-kernel@lists.linaro.org" , "khilman@linaro.org" Subject: Re: [PATCH v5 1/2] arm64: adjust el0_sync so that a function can be called Message-ID: <20140529175236.GA24270@arm.com> References: <1401130573-7443-1-git-send-email-larry.bassel@linaro.org> <1401130573-7443-2-git-send-email-larry.bassel@linaro.org> <20140528112738.GE15222@arm.com> <20140528193542.GD7953@ubuette> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140528193542.GD7953@ubuette> 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 Wed, May 28, 2014 at 08:35:51PM +0100, Larry Bassel wrote: > On 28 May 14 12:27, Will Deacon wrote: > > On Mon, May 26, 2014 at 07:56:12PM +0100, Larry Bassel wrote: > > > To implement the context tracker properly on arm64, > > > a function call needs to be made after debugging and > > > interrupts are turned on, but before the lr is changed > > > to point to ret_to_user(). If the function call > > > is made after the lr is changed the function will not > > > return to the correct place. > > > > > > For similar reasons, defer the setting of x0 so that > > > it doesn't need to be saved around the function call > > > (save far_el1 in x26 temporarily instead). > > > > > > Signed-off-by: Larry Bassel > > > > [...] > > > > > > Why have you added this mov instruction? > > I believe (please correct me if I'm wrong) that it is necessary. > Here is why: > > > > @@ -476,23 +481,27 @@ el0_undef: > > > // enable interrupts before calling the main handler > > > enable_dbg_and_irq > > > mov x0, sp > > > + adr lr, ret_to_user > > > b do_undefinstr > > > el0_dbg: > > > /* > > > * Debug exception handling > > > */ > > > tbnz x24, #0, el0_inv // EL0 only > > > - mrs x0, far_el1 > > > + mrs x26, far_el1 > > needed because do_debug_exception may clobber x0, so save far_el1 > in x26 (as other parts of this patch do) Actually, do_debug_exception consumes the FAR as its first parameter, so you don't need to put this in x26 afaict. > > > + mov x0, x26 > > needed because far_el1 is expected to be in x0 here > > > > mov x1, x25 > > > mov x2, sp > > > bl do_debug_exception > > > enable_dbg > > [call to ct_user_exit will go here in the next patch, this may re-clobber x0] > > > > + mov x0, x26 > > needed because far_el1 is expected to be in x0 here Is it? ret_to_user doesn't care. Does ct_user_exit use the FAR? I don't think it does... Will