From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753426AbbDCIVy (ORCPT ); Fri, 3 Apr 2015 04:21:54 -0400 Received: from terminus.zytor.com ([198.137.202.10]:44821 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753404AbbDCIVs (ORCPT ); Fri, 3 Apr 2015 04:21:48 -0400 Date: Fri, 3 Apr 2015 01:21:22 -0700 From: tip-bot for Andy Lutomirski Message-ID: Cc: brgerst@gmail.com, dvlasenk@redhat.com, bp@alien8.de, mingo@kernel.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de, luto@amacapital.net, hpa@zytor.com Reply-To: brgerst@gmail.com, dvlasenk@redhat.com, bp@alien8.de, mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, luto@amacapital.net, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org In-Reply-To: <05a0163eb33ef5208363f0015496855da7cebadd.1428002830.git.luto@kernel.org> References: <05a0163eb33ef5208363f0015496855da7cebadd.1428002830.git.luto@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/asm/entry/32: Stop caching MSR_IA32_SYSENTER_ESP in tss.sp1 Git-Commit-ID: cf9328cc9989e028fdc64d8c0a7b1b043dc96735 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: cf9328cc9989e028fdc64d8c0a7b1b043dc96735 Gitweb: http://git.kernel.org/tip/cf9328cc9989e028fdc64d8c0a7b1b043dc96735 Author: Andy Lutomirski AuthorDate: Thu, 2 Apr 2015 12:41:45 -0700 Committer: Ingo Molnar CommitDate: Fri, 3 Apr 2015 08:30:44 +0200 x86/asm/entry/32: Stop caching MSR_IA32_SYSENTER_ESP in tss.sp1 We write a stack pointer to MSR_IA32_SYSENTER_ESP exactly once, and we unnecessarily cache the value in tss.sp1. We never read the cached value. Remove all of the caching. It serves no purpose. Suggested-by: Denys Vlasenko Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/05a0163eb33ef5208363f0015496855da7cebadd.1428002830.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/processor.h | 22 +++++++++++----------- arch/x86/kernel/cpu/common.c | 9 +++++---- 2 files changed, 16 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 5720997..d2203b5 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -209,21 +209,21 @@ struct x86_hw_tss { unsigned short back_link, __blh; unsigned long sp0; unsigned short ss0, __ss0h; + unsigned long sp1; /* - * We don't use ring 1, so sp1 and ss1 are convenient scratch - * spaces in the same cacheline as sp0. We use them to cache - * some MSR values to avoid unnecessary wrmsr instructions. + * We don't use ring 1, so ss1 is a convenient scratch space in + * the same cacheline as sp0. We use ss1 to cache the value in + * MSR_IA32_SYSENTER_CS. When we context switch + * MSR_IA32_SYSENTER_CS, we first check if the new value being + * written matches ss1, and, if it's not, then we wrmsr the new + * value and update ss1. * - * We use SYSENTER_ESP to find sp0 and for the NMI emergency - * stack, but we need to context switch it because we do - * horrible things to the kernel stack in vm86 mode. - * - * We use SYSENTER_CS to disable sysenter in vm86 mode to avoid - * corrupting the stack if we went through the sysenter path - * from vm86 mode. + * The only reason we context switch MSR_IA32_SYSENTER_CS is + * that we set it to zero in vm86 tasks to avoid corrupting the + * stack if we were to go through the sysenter path from vm86 + * mode. */ - unsigned long sp1; /* MSR_IA32_SYSENTER_ESP */ unsigned short ss1; /* MSR_IA32_SYSENTER_CS */ unsigned short __ss1h; diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 71e4adc..a383d53 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -976,15 +976,16 @@ void enable_sep_cpu(void) goto out; /* - * The struct::SS1 and tss_struct::SP1 fields are not used by the hardware, - * we cache the SYSENTER CS and ESP values there for easy access: + * We cache MSR_IA32_SYSENTER_CS's value in the TSS's ss1 field -- + * see the big comment in struct x86_hw_tss's definition. */ tss->x86_tss.ss1 = __KERNEL_CS; wrmsr(MSR_IA32_SYSENTER_CS, tss->x86_tss.ss1, 0); - tss->x86_tss.sp1 = (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack); - wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.sp1, 0); + wrmsr(MSR_IA32_SYSENTER_ESP, + (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack), + 0); wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)ia32_sysenter_target, 0);