From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753720AbbHaQIv (ORCPT ); Mon, 31 Aug 2015 12:08:51 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35712 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752792AbbHaQIt (ORCPT ); Mon, 31 Aug 2015 12:08:49 -0400 Message-ID: <1441037316.25485.4.camel@fourier> Subject: Re: [PATCH 3.19.y-ckt 130/130] Revert "sched/x86_64: Don't save flags on context switch" From: Kamal Mostafa To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , stable , kernel-team@lists.ubuntu.com, Andy Lutomirski , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Ingo Molnar Date: Mon, 31 Aug 2015 09:08:36 -0700 In-Reply-To: References: <1440713521-5906-1-git-send-email-kamal@canonical.com> <1440713521-5906-131-git-send-email-kamal@canonical.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2015-08-29 at 09:20 -0700, Andy Lutomirski wrote: > If you haven't pushed this out yet, I would hold off. I think it may > be unnecessary. Okay, I've dropped this revert from the 3.19-stable queue. And for reference, your post: http://seclists.org/oss-sec/2015/q3/456 Thanks very much for the heads-up, Andy. -Kamal > On Thu, Aug 27, 2015 at 3:12 PM, Kamal Mostafa wrote: > > 3.19.8-ckt6 -stable review patch. If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Andy Lutomirski > > > > commit 512255a2ad2c832ca7d4de9f31245f73781922d0 upstream. > > > > This reverts commit: > > > > 2c7577a75837 ("sched/x86_64: Don't save flags on context switch") > > > > It was a nice speedup. It's also not quite correct: SYSENTER > > enables interrupts too early. > > > > We can re-add this optimization once the SYSENTER code is beaten > > into shape, which should happen in 4.3 or 4.4. > > > > Signed-off-by: Andy Lutomirski > > Cc: Linus Torvalds > > Cc: Peter Zijlstra > > Cc: Thomas Gleixner > > Link: http://lkml.kernel.org/r/85f56651f59f76624e80785a8fd3bdfdd089a818.1439838962.git.luto@kernel.org > > Signed-off-by: Ingo Molnar > > Signed-off-by: Kamal Mostafa > > --- > > arch/x86/include/asm/switch_to.h | 12 ++++-------- > > 1 file changed, 4 insertions(+), 8 deletions(-) > > > > diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h > > index 751bf4b..d7f3b3b 100644 > > --- a/arch/x86/include/asm/switch_to.h > > +++ b/arch/x86/include/asm/switch_to.h > > @@ -79,12 +79,12 @@ do { \ > > #else /* CONFIG_X86_32 */ > > > > /* frame pointer must be last for get_wchan */ > > -#define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t" > > -#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t" > > +#define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t" > > +#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t" > > > > #define __EXTRA_CLOBBER \ > > , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \ > > - "r12", "r13", "r14", "r15", "flags" > > + "r12", "r13", "r14", "r15" > > > > #ifdef CONFIG_CC_STACKPROTECTOR > > #define __switch_canary \ > > @@ -100,11 +100,7 @@ do { \ > > #define __switch_canary_iparam > > #endif /* CC_STACKPROTECTOR */ > > > > -/* > > - * There is no need to save or restore flags, because flags are always > > - * clean in kernel mode, with the possible exception of IOPL. Kernel IOPL > > - * has no effect. > > - */ > > +/* Save restore flags to clear handle leaking NT */ > > #define switch_to(prev, next, last) \ > > asm volatile(SAVE_CONTEXT \ > > "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \ > > -- > > 1.9.1 > > > > >