Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756741AbbHZLMI (ORCPT ); Wed, 26 Aug 2015 07:12:08 -0400 Received: from foss.arm.com ([217.140.101.70]:44494 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756386AbbHZLMG (ORCPT ); Wed, 26 Aug 2015 07:12:06 -0400 Date: Wed, 26 Aug 2015 12:12:05 +0100 From: Will Deacon To: Chunyan Zhang Cc: Catalin Marinas , "linux-arm-kernel@lists.infradead.org" , "jianhua.ljh@gmail.com" , "orson.zhai@spreadtrum.com" , "xiongshan.an@spreadtrum.com" , "linux-kernel@vger.kernel.org" , ard.biesheuvel@linaro.org Subject: Re: [PATCH] arm64: fix bug for reloading FPSIMD state after execve on cpu 0. Message-ID: <20150826111205.GD30466@arm.com> References: <1440556841-17219-1-git-send-email-chunyan.zhang@spreadtrum.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1440556841-17219-1-git-send-email-chunyan.zhang@spreadtrum.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 Content-Length: 1751 Lines: 49 Hello, [adding Ard] On Wed, Aug 26, 2015 at 03:40:41AM +0100, Chunyan Zhang wrote: > From: Janet Liu > > If process A is running on CPU 0 and do execve syscall and after sched_exec, > dest_cpu is 0, fpsimd_state.cpu is 0. If at the time Process A get scheduled > out and after some kernel threads running on CPU 0, process A is back in CPU 0, > A's fpsimd_state.cpu is current cpu id "0", and per_cpu(fpsimd_last_state) > points A's fpsimd_state, TIF_FOREIGN_FPSTATE will be clear, kernel will not > reload the context during it return to userspace. so set the cpu's > fpsimd_last_state to NULL to avoid this. AFAICT, this is only a problem if one of the kernel threads uses the fpsimd registers, right? However, kernel_neon_begin_partial clobbers fpsimd_last_state, so I'm struggling to see the problem. Are you seeing an issue in practice? Will > Signed-off-by: Janet Liu > Signed-off-by: Chunyan Zhang > --- > arch/arm64/kernel/fpsimd.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index 44d6f75..ec58d94 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -159,6 +159,7 @@ void fpsimd_flush_thread(void) > { > memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); > set_thread_flag(TIF_FOREIGN_FPSTATE); > + this_cpu_write(fpsimd_last_state, NULL); > } > > /* > -- > 1.7.9.5 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/