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 X-Spam-Level: X-Spam-Status: No, score=-4.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,RDNS_NONE,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_NONE autolearn=no autolearn_force=no version=3.4.0 Received: from mail.skyhub.de ([5.9.137.197]:40062 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730052AbgCKQRt (ORCPT ); Wed, 11 Mar 2020 12:17:49 -0400 Date: Wed, 11 Mar 2020 17:17:56 +0100 From: Borislav Petkov To: Qian Cai Cc: tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, elver@google.com, x86@kernel.org, linux-kernel@vger.kernel.org, "Paul E. McKenney" Subject: Re: [PATCH -next] x86/mm/pat: mark an intentional data race Message-ID: <20200311161756.GE3470@zn.tnic> References: <1581343816-6490-1-git-send-email-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1581343816-6490-1-git-send-email-cai@lca.pw> Sender: linux-kernel-owner@vger.kernel.org List-ID: + Paul. On Mon, Feb 10, 2020 at 09:10:16AM -0500, Qian Cai wrote: > cpa_4k_install could be accessed concurrently as noticed by KCSAN, > > read to 0xffffffffaa59a000 of 8 bytes by interrupt on cpu 7: > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > __change_page_attr+0x10cf/0x1840 arch/x86/mm/pat/set_memory.c:1514 > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > __set_pages_np+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2148 > __kernel_map_pages+0xb0/0xc8 arch/x86/mm/pat/set_memory.c:2178 > kernel_map_pages include/linux/mm.h:2719 [inline] > > write to 0xffffffffaa59a000 of 8 bytes by task 1 on cpu 6: > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > __change_page_attr+0x10ea/0x1840 arch/x86/mm/pat/set_memory.c:1514 > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > __set_pages_p+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2129 > __kernel_map_pages+0x2e/0xc8 arch/x86/mm/pat/set_memory.c:2176 > kernel_map_pages include/linux/mm.h:2719 [inline] > > Both accesses are due to the same "cpa_4k_install++" in > cpa_inc_4k_install. A data race here could be potentially undesirable: > depending on compiler optimizations or how x86 executes a non-LOCK'd > increment, it may lose increments, corrupt the counter, etc. Since this > counter only seems to be used for printing some stats, this data race > itself is unlikely to cause harm to the system though. Thus, mark this > intentional data race using the data_race() marco. > > Suggested-by: Macro Elver > Signed-off-by: Qian Cai > --- > arch/x86/mm/pat/set_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index c4aedd00c1ba..ea0b6df950ee 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -128,7 +128,7 @@ static inline void cpa_inc_2m_checked(void) > > static inline void cpa_inc_4k_install(void) > { > - cpa_4k_install++; > + data_race(cpa_4k_install++); > } > > static inline void cpa_inc_lp_sameprot(int level) > -- Acked-by: Borislav Petkov -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette