From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932929AbcKPSXg (ORCPT ); Wed, 16 Nov 2016 13:23:36 -0500 Received: from mail.kernel.org ([198.145.29.136]:49772 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753836AbcKPSXe (ORCPT ); Wed, 16 Nov 2016 13:23:34 -0500 From: Andy Lutomirski To: x86@kernel.org Cc: Borislav Petkov , linux-kernel@vger.kernel.org, Megha , Andy Lutomirski Subject: [PATCH 1/2] x86/vdso: Use RDPID in preference to LSL when available Date: Wed, 16 Nov 2016 10:23:27 -0800 Message-Id: <4f6c3a22012d10f1c65b9ca15800e01b42c7d39d.1479320367.git.luto@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org RDPID is a new instruction that reads MSR_TSC_AUX quickly. This should be considerably faster than reading the GDT. Add a cpufeature for it and use it from __vdso_getcpu when available. Tested-by: Megha Dey Signed-off-by: Andy Lutomirski --- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/vgtod.h | 7 ++++++- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index a39629206864..3068edf43abe 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -281,6 +281,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ecx), word 16 */ #define X86_FEATURE_PKU (16*32+ 3) /* Protection Keys for Userspace */ #define X86_FEATURE_OSPKE (16*32+ 4) /* OS Protection Keys Enable */ +#define X86_FEATURE_RDPID (16*32+ 22) /* RDPID instruction */ /* AMD-defined CPU features, CPUID level 0x80000007 (ebx), word 17 */ #define X86_FEATURE_OVERFLOW_RECOV (17*32+0) /* MCA overflow recovery support */ diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index e728699db774..3a01996db58f 100644 --- a/arch/x86/include/asm/vgtod.h +++ b/arch/x86/include/asm/vgtod.h @@ -89,8 +89,13 @@ static inline unsigned int __getcpu(void) * works on all CPUs. This is volatile so that it orders * correctly wrt barrier() and to keep gcc from cleverly * hoisting it out of the calling function. + * + * If RDPID is available, use it. */ - asm volatile ("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG)); + alternative_io ("lsl %[p],%[seg]", + ".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */ + X86_FEATURE_RDPID, + [p] "=a" (p), [seg] "r" (__PER_CPU_SEG)); return p; } -- 2.7.4