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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 30ED1C433F5 for ; Fri, 10 Dec 2021 11:24:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=BeOm8BFwB4Whdz9/cEjrCip4ZYio5AlAfxkXPbxfrE4=; b=r3vJ5V/4ejel4W 4wbssNPJ1WfHA/jyyWJnPh0dEGVc4ccsRRXstLMV2Bbueh/Rl6XjTrZQOQMoEdVD5gAjI5cDWlJ/U PFAQ+pBVpmI/de5c3uhY7BGxEEyPLl6zfK0s8+YUHZ3qGutQJF0nvA0NoMF/FDJX1LfV/OWNgUXCT tL3ONdqqgAQs9tsrPy0z/2uVGenyyxDGCczRFMJYYH4m6HnQOZ2cc9Z0HwHbsHlDxiGSJs/Z17TFS uMMVRn8x4EPY+9nhmtMjAtbNbubC/kEIyNHaWyTdWFOACOWn4E9Tl6SlMH9wRlovokKnB+ps2etQv dJm6lLA7BPfqkY04rAlA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvdzR-001e7b-FU; Fri, 10 Dec 2021 11:23:01 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvdyj-001dsZ-2x for linux-arm-kernel@lists.infradead.org; Fri, 10 Dec 2021 11:22:18 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id C4499B827CA; Fri, 10 Dec 2021 11:22:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C061C00446; Fri, 10 Dec 2021 11:22:12 +0000 (UTC) Date: Fri, 10 Dec 2021 11:22:09 +0000 From: Catalin Marinas To: Jianyong Wu Cc: will@kernel.org, anshuman.khandual@arm.com, akpm@linux-foundation.org, ardb@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, david@redhat.com, gshan@redhat.com, justin.he@arm.com, nd@arm.com, Mark Rutland Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Message-ID: References: <20211210095432.51798-1-jianyong.wu@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211210095432.51798-1-jianyong.wu@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211210_032217_299501_FD51FB50 X-CRM114-Status: GOOD ( 13.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Dec 10, 2021 at 05:54:32PM +0800, Jianyong Wu wrote: > fixmap is a global resource and is used recursively in create pud mapping. > It may lead to race condition when alloc_init_pud is called concurrently. > > Fox example: > alloc_init_pud is called when kernel_init. If memory hotplug > thread, which will also call alloc_init_pud, happens during > kernel_init, the race for fixmap occurs. > > The race condition flow can be: > > *************** begin ************** > > kerenl_init thread virtio-mem workqueue thread > ================== ======== ================== > alloc_init_pud(...) > pudp = pud_set_fixmap_offset(..) alloc_init_pud(...) > ... ... > READ_ONCE(*pudp) //OK! pudp = pud_set_fixmap_offset( > ... ... > pud_clear_fixmap() //fixmap break > READ_ONCE(*pudp) //CRASH! > > **************** end *************** > > Hence, a spin lock is introduced to protect the fixmap during create pdg > mapping. > > Signed-off-by: Jianyong Wu It looks fine to me: Reviewed-by: Catalin Marinas Do we need a cc stable? Fixmap was introduced in 4.6, so usually: Fixes: f4710445458c ("arm64: mm: use fixmap when creating page tables") Cc: # 4.6.x but I haven't checked when memory hotplug was added to be able to trigger the race. It may not need to go back that far. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 0032EC433EF for ; Fri, 10 Dec 2021 11:22:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240172AbhLJLZx (ORCPT ); Fri, 10 Dec 2021 06:25:53 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:48976 "EHLO sin.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237570AbhLJLZw (ORCPT ); Fri, 10 Dec 2021 06:25:52 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 75F4ECE2AB7 for ; Fri, 10 Dec 2021 11:22:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C061C00446; Fri, 10 Dec 2021 11:22:12 +0000 (UTC) Date: Fri, 10 Dec 2021 11:22:09 +0000 From: Catalin Marinas To: Jianyong Wu Cc: will@kernel.org, anshuman.khandual@arm.com, akpm@linux-foundation.org, ardb@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, david@redhat.com, gshan@redhat.com, justin.he@arm.com, nd@arm.com, Mark Rutland Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Message-ID: References: <20211210095432.51798-1-jianyong.wu@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211210095432.51798-1-jianyong.wu@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 10, 2021 at 05:54:32PM +0800, Jianyong Wu wrote: > fixmap is a global resource and is used recursively in create pud mapping. > It may lead to race condition when alloc_init_pud is called concurrently. > > Fox example: > alloc_init_pud is called when kernel_init. If memory hotplug > thread, which will also call alloc_init_pud, happens during > kernel_init, the race for fixmap occurs. > > The race condition flow can be: > > *************** begin ************** > > kerenl_init thread virtio-mem workqueue thread > ================== ======== ================== > alloc_init_pud(...) > pudp = pud_set_fixmap_offset(..) alloc_init_pud(...) > ... ... > READ_ONCE(*pudp) //OK! pudp = pud_set_fixmap_offset( > ... ... > pud_clear_fixmap() //fixmap break > READ_ONCE(*pudp) //CRASH! > > **************** end *************** > > Hence, a spin lock is introduced to protect the fixmap during create pdg > mapping. > > Signed-off-by: Jianyong Wu It looks fine to me: Reviewed-by: Catalin Marinas Do we need a cc stable? Fixmap was introduced in 4.6, so usually: Fixes: f4710445458c ("arm64: mm: use fixmap when creating page tables") Cc: # 4.6.x but I haven't checked when memory hotplug was added to be able to trigger the race. It may not need to go back that far. -- Catalin