From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:52921 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752533AbbHSQYG (ORCPT ); Wed, 19 Aug 2015 12:24:06 -0400 Date: Wed, 19 Aug 2015 17:23:59 +0100 From: Will Deacon To: Catalin Marinas Cc: "linux-arm-kernel@lists.infradead.org" , Kevin Hilman , "stable@vger.kernel.org" , "hanjun.guo@linaro.org" , Larry Bassel Subject: Re: [PATCH] arm64: entry: always restore x0 from the stack on syscall return Message-ID: <20150819162359.GA10297@arm.com> References: <1439996989-5772-1-git-send-email-will.deacon@arm.com> <20150819160320.GI24062@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150819160320.GI24062@e104818-lin.cambridge.arm.com> Sender: stable-owner@vger.kernel.org List-ID: On Wed, Aug 19, 2015 at 05:03:20PM +0100, Catalin Marinas wrote: > On Wed, Aug 19, 2015 at 04:09:49PM +0100, Will Deacon wrote: > > @@ -613,13 +609,14 @@ ENDPROC(cpu_switch_to) > > */ > > ret_fast_syscall: > > disable_irq // disable interrupts > > + str x0, [sp, #S_X0] // returned x0 > > ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing > > and x2, x1, #_TIF_SYSCALL_WORK > > cbnz x2, ret_fast_syscall_trace > > and x2, x1, #_TIF_WORK_MASK > > - cbnz x2, fast_work_pending > > + cbnz x2, work_pending > > enable_step_tsk x1, x2 > > - kernel_exit 0, ret = 1 > > + kernel_exit 0 > > ret_fast_syscall_trace: > > enable_irq // enable interrupts > > b __sys_trace_return > > There is another str x0 in __sys_trace_return which I think we could > remove. Hmm, I don't think we can remove that. It's needed on the slowpath to update the pt_regs with either -ENOSYS (for __ni_sys_trace) or the syscall return value from the blr in __sys_trace. What we can do instead is change the branch above to branch to __sys_trace_return_skipped. Patch below. Will --->8 diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 2a5e64ccc991..088322ff1ba0 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -619,7 +619,7 @@ ret_fast_syscall: kernel_exit 0 ret_fast_syscall_trace: enable_irq // enable interrupts - b __sys_trace_return + b __sys_trace_return_skipped // we already saved x0 /* * Ok, we need to do extra processing, enter the slow path.