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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5528C433F5 for ; Wed, 27 Oct 2021 09:50:02 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 70B7960EDF for ; Wed, 27 Oct 2021 09:50:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 70B7960EDF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org 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:MIME-Version:List-Subscribe:List-Help: List-Post:List-Archive:List-Unsubscribe:List-Id:Message-Id:Date:Subject:Cc:To :From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=ut9JK+jrL91vD44hoMc7sJWmFs45EjVyD0eTBtsmgBY=; b=OeTRCrUtXK4lmY nWODqfEOMRwxrKkicyF8WtMvYvki8KJGm5rJ74amKiebdWe4kKDp+ws7BcHqfWT+zYr6K5fhEGcUB n6jXUTLUv/7Qai4zcyhi2tfxDFuH9PSsMBIbnrmdiif/364DokShXK40Bm9/NMECg0TUST9xx91qI t59Vxt+iwvqBrbD7EkCxLyt7ox9ALkQNYugrDiku74LtJziBaCCjtcha4eJzKFVJwH9/aV5R64KzD ObSeFMsk73sqgqd8wBx+o7HBlZmlnD3DwaujKQwyDT38pfqpI1Dkuav2e9o0X7uCmcx07LW/JnZns GYG1gM6TdupFi++Az47g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mffY7-004TVS-Ob; Wed, 27 Oct 2021 09:48:47 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mffY3-004TTU-2w for linux-arm-kernel@lists.infradead.org; Wed, 27 Oct 2021 09:48:45 +0000 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 3A6461FB; Wed, 27 Oct 2021 02:48:39 -0700 (PDT) Received: from entos-thunderx2-desktop.shanghai.arm.com (entos-thunderx2-desktop.shanghai.arm.com [10.169.212.208]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 968C43F70D; Wed, 27 Oct 2021 02:48:35 -0700 (PDT) From: Jianyong Wu To: catalin.marinas@arm.com, will@kernel.org Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, maz@kernel.org, anshuman.khandual@arm.com, ardb@kernel.org, david@redhat.com, gshan@redhat.com, justin.he@arm.com, jianyong.wu@arm.com, nd@arm.com Subject: [PATCH v1] arm64/mm: avoid race condition of update page table when kernel init Date: Wed, 27 Oct 2021 17:48:28 +0800 Message-Id: <20211027094828.7629-1-jianyong.wu@arm.com> X-Mailer: git-send-email 2.17.1 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211027_024843_301036_FF5CE66C X-CRM114-Status: GOOD ( 15.03 ) 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: , MIME-Version: 1.0 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 Race condition of page table update can happen in kernel boot period as both of memory hotplug action when kernel init and the mark_rodata_ro can update page table. For virtio-mem, the function excute flow chart is: ------------------------- kernel_init kernel_init_freeable ... do_initcall ... module_init [A] ... mark_readonly mark_rodata_ro [B] ------------------------- virtio-mem can be initialized at [A] and spwan a workqueue to add memory, therefore the race of update page table can happen inside [B]. What's more, the race condition can happen even for ACPI based memory hotplug, as it can burst into kernel boot period while page table is updating inside mark_rodata_ro. That's why memory hotplug lock is needed to guard mark_rodata_ro to avoid the race condition. It may only happen in arm64. As fixmap, which is the global resource, is used in page table creating. So, the change is only for arm64. The error often occurs inside alloc_init_pud() in arch/arm64/mm/mmu.c the race condition flow is: *************** begin ************ kerenl_init virtio-mem workqueue ========= ======== 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 ************* I catch the related error when test virtio-mem (a new memory hotplug driver) on arm64. How to reproduce: (1) prepare a kernel with virtio-mem enabled on arm64 (2) start a VM using Cloud Hypervisor using the kernel above (3) hotplug memory, 20G in my case, with virtio-mem (4) reboot or start a new kernel using kexec Test for server times, you may find the error below: [ 1.131039] Unable to handle kernel paging request at virtual address fffffbfffda3b140 [ 1.134504] Mem abort info: [ 1.135722] ESR = 0x96000007 [ 1.136991] EC = 0x25: DABT (current EL), IL = 32 bits [ 1.139189] SET = 0, FnV = 0 [ 1.140467] EA = 0, S1PTW = 0 [ 1.141755] FSC = 0x07: level 3 translation fault [ 1.143787] Data abort info: [ 1.144976] ISV = 0, ISS = 0x00000007 [ 1.146554] CM = 0, WnR = 0 [ 1.147817] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000426f2000 [ 1.150551] [fffffbfffda3b140] pgd=0000000042ffd003, p4d=0000000042ffd003, pud=0000000042ffe003, pmd=0000000042fff003, pte=0000000000000000 [ 1.155728] Internal error: Oops: 96000007 [#1] SMP [ 1.157724] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G C 5.15.0-rc3+ #100 [ 1.161002] Hardware name: linux,dummy-virt (DT) [ 1.162939] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 1.165825] pc : alloc_init_pud+0x38c/0x550 [ 1.167610] lr : alloc_init_pud+0x394/0x550 [ 1.169358] sp : ffff80001001bd10 ...... [ 1.200527] Call trace: [ 1.201583] alloc_init_pud+0x38c/0x550 [ 1.203218] __create_pgd_mapping+0x94/0xe0 [ 1.204983] update_mapping_prot+0x50/0xd8 [ 1.206730] mark_rodata_ro+0x50/0x58 [ 1.208281] kernel_init+0x3c/0x120 [ 1.209760] ret_from_fork+0x10/0x20 [ 1.211298] Code: eb15003f 54000061 d5033a9f d5033fdf (f94000a1) [ 1.213856] ---[ end trace 59473413ffe3f52d ]--- [ 1.215850] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b We can see that the error derived from the l3 translation as the pte value is *0*. That is because the fixmap has been clear when access. Signed-off-by: Jianyong Wu --- arch/arm64/mm/mmu.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index cfd9deb347c3..567dfba8f08a 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -564,8 +564,10 @@ void mark_rodata_ro(void) * to cover NOTES and EXCEPTION_TABLE. */ section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata; + get_online_mems(); update_mapping_prot(__pa_symbol(__start_rodata), (unsigned long)__start_rodata, section_size, PAGE_KERNEL_RO); + put_online_mems(); debug_checkwx(); } -- 2.17.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel