From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D748C433FE for ; Tue, 3 May 2022 14:20:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230012AbiECOYW (ORCPT ); Tue, 3 May 2022 10:24:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237028AbiECOXu (ORCPT ); Tue, 3 May 2022 10:23:50 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DE8541136 for ; Tue, 3 May 2022 07:20:14 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 934D51042; Tue, 3 May 2022 07:20:14 -0700 (PDT) Received: from lakrids (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 55AB63F774; Tue, 3 May 2022 07:20:13 -0700 (PDT) Date: Tue, 3 May 2022 15:20:06 +0100 From: Mark Rutland To: Josh Poimboeuf Cc: Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org, elver@google.com, jbaron@akamai.com, rostedt@goodmis.org, ardb@kernel.org, kernel test robot Subject: Re: [PATCH 2/3] x86/cpu: Elide KCSAN for cpu_has() and friends Message-ID: References: <20220502110741.951055904@infradead.org> <20220502111216.290518605@infradead.org> <20220502184747.cr5ssem3g4mel4qq@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220502184747.cr5ssem3g4mel4qq@treble> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 02, 2022 at 11:47:47AM -0700, Josh Poimboeuf wrote: > On Mon, May 02, 2022 at 01:07:43PM +0200, Peter Zijlstra wrote: > > vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section > > vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section > > vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section > > vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section > > > > Reported-by: kernel test robot > > Signed-off-by: Peter Zijlstra (Intel) > > An explanation about *why* this fixes it would help, as I have no idea > from looking at the patch. How about something like: | As x86 uses the headers, the | regular forms of all bitops are instrumented with explicit calls to | KASAN and KCSAN checks. As these are explicit calls, these are not | suppressed by the noinstr function attribute. | | This can result in calls to those check functions in noinstr code, which | objtool warns about: | | vmlinux.o: warning: objtool: enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section | vmlinux.o: warning: objtool: syscall_enter_from_user_mode+0x28: call to __kcsan_check_access() leaves .noinstr.text section | vmlinux.o: warning: objtool: syscall_enter_from_user_mode_prepare+0x24: call to __kcsan_check_access() leaves .noinstr.text section | vmlinux.o: warning: objtool: irqentry_enter_from_user_mode+0x24: call to __kcsan_check_access() leaves .noinstr.text section | | Prevent this by using the arch_*() bitops, which are the underlying | bitops without explciit instrumentation. Thanks, Mark. > > > --- > > arch/x86/include/asm/cpufeature.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > --- a/arch/x86/include/asm/cpufeature.h > > +++ b/arch/x86/include/asm/cpufeature.h > > @@ -51,7 +51,7 @@ extern const char * const x86_power_flag > > extern const char * const x86_bug_flags[NBUGINTS*32]; > > > > #define test_cpu_cap(c, bit) \ > > - test_bit(bit, (unsigned long *)((c)->x86_capability)) > > + arch_test_bit(bit, (unsigned long *)((c)->x86_capability)) > > > > /* > > * There are 32 bits/features in each mask word. The high bits > > > > > > -- > Josh >