Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758006Ab0GOAzn (ORCPT ); Wed, 14 Jul 2010 20:55:43 -0400 Received: from claw.goop.org ([74.207.240.146]:45400 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757614Ab0GOAzl (ORCPT ); Wed, 14 Jul 2010 20:55:41 -0400 Message-ID: <4C3E5C8C.8000800@goop.org> Date: Wed, 14 Jul 2010 17:55:40 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.10) Gecko/20100621 Fedora/3.0.5-1.fc13 Lightning/1.0b2pre Thunderbird/3.0.5 MIME-Version: 1.0 To: Zachary Amsden CC: Glauber Costa , "H. Peter Anvin" , Thomas Gleixner , Avi Kivity , Linux Kernel Mailing List Subject: Re: [PATCH] x86: fix ordering constraints on crX read/writes References: <4C3E363B.7060804@goop.org> <4C3E5637.4010300@redhat.com> In-Reply-To: <4C3E5637.4010300@redhat.com> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2620 Lines: 85 On 07/14/2010 05:28 PM, Zachary Amsden wrote: > >> static inline void native_write_cr2(unsigned long val) >> { >> - asm volatile("mov %0,%%cr2": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr2": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> > > > You don't need the memory clobber there. Technically, this should > never be used, however. Yes. I just did it for consistency. Likewise, I didn't pore over the manuals to work out whether writes to any crX could really have memory side-effects. >> >> static inline unsigned long native_read_cr3(void) >> { >> unsigned long val; >> - asm volatile("mov %%cr3,%0\n\t" : "=r" (val), "=m" >> (__force_order)); >> + asm volatile("mov %%cr3,%0\n\t" : "=r" (val) : "m" >> (__force_order)); >> return val; >> } >> >> static inline void native_write_cr3(unsigned long val) >> { >> - asm volatile("mov %0,%%cr3": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr3": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> >> static inline unsigned long native_read_cr4(void) >> { >> unsigned long val; >> - asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" >> (__force_order)); >> + asm volatile("mov %%cr4,%0\n\t" : "=r" (val) : "m" >> (__force_order)); >> return val; >> } >> >> @@ -271,7 +286,7 @@ static inline unsigned long >> native_read_cr4_safe(void) >> asm volatile("1: mov %%cr4, %0\n" >> "2:\n" >> _ASM_EXTABLE(1b, 2b) >> - : "=r" (val), "=m" (__force_order) : "0" (0)); >> + : "=r" (val) : "m" (__force_order), "0" (0)); >> #else >> val = native_read_cr4(); >> #endif >> @@ -280,7 +295,7 @@ static inline unsigned long >> native_read_cr4_safe(void) >> >> static inline void native_write_cr4(unsigned long val) >> { >> - asm volatile("mov %0,%%cr4": : "r" (val), "m" (__force_order)); >> + asm volatile("mov %1,%%cr4": "+m" (__force_order) : "r" (val) : >> "memory"); >> } >> >> #ifdef CONFIG_X86_64 >> >> >> > > Looks good. I really hope __force_order gets pruned however. Does it > actually? There's a couple of instances in my vmlinux. I didn't try to track them back to specific .o files. gcc tends to generate references by putting its address into a register and passing that into the asms. J -- 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/