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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C56DC5B57E for ; Sun, 30 Jun 2019 08:50:14 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8A6A62070D for ; Sun, 30 Jun 2019 08:50:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A6A62070D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45c42X0MnwzDqjV for ; Sun, 30 Jun 2019 18:50:12 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45c3lq6n4czDqp7 for ; Sun, 30 Jun 2019 18:37:27 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix, from userid 1034) id 45c3lq3P7hz9sCJ; Sun, 30 Jun 2019 18:37:27 +1000 (AEST) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: f474c28fbcbe42faca4eb415172c07d76adcb819 X-Patchwork-Hint: ignore In-Reply-To: <20190613033014.17496-1-ravi.bangoria@linux.ibm.com> To: Ravi Bangoria From: Michael Ellerman Subject: Re: [PATCH v2] Powerpc/Watchpoint: Restore nvgprs while returning from exception Message-Id: <45c3lq3P7hz9sCJ@ozlabs.org> Date: Sun, 30 Jun 2019 18:37:27 +1000 (AEST) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: ravi.bangoria@linux.ibm.com, mikey@neuling.org, aneesh.kumar@linux.ibm.com, linux-kernel@vger.kernel.org, npiggin@gmail.com, paulus@samba.org, mahesh@linux.vnet.ibm.com, naveen.n.rao@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, 2019-06-13 at 03:30:14 UTC, Ravi Bangoria wrote: > Powerpc hw triggers watchpoint before executing the instruction. To > make trigger-after-execute behavior, kernel emulates the instruction. > If the instruction is 'load something into non-volatile register', > exception handler should restore emulated register state while > returning back, otherwise there will be register state corruption. > Ex, Adding a watchpoint on a list can corrput the list: > > # cat /proc/kallsyms | grep kthread_create_list > c00000000121c8b8 d kthread_create_list > > Add watchpoint on kthread_create_list->prev: > > # perf record -e mem:0xc00000000121c8c0 > > Run some workload such that new kthread gets invoked. Ex, I just > logged out from console: > > list_add corruption. next->prev should be prev (c000000001214e00), \ > but was c00000000121c8b8. (next=c00000000121c8b8). > WARNING: CPU: 59 PID: 309 at lib/list_debug.c:25 __list_add_valid+0xb4/0xc0 > CPU: 59 PID: 309 Comm: kworker/59:0 Kdump: loaded Not tainted 5.1.0-rc7+ #69 > ... > NIP __list_add_valid+0xb4/0xc0 > LR __list_add_valid+0xb0/0xc0 > Call Trace: > __list_add_valid+0xb0/0xc0 (unreliable) > __kthread_create_on_node+0xe0/0x260 > kthread_create_on_node+0x34/0x50 > create_worker+0xe8/0x260 > worker_thread+0x444/0x560 > kthread+0x160/0x1a0 > ret_from_kernel_thread+0x5c/0x70 > > List corruption happened because it uses 'load into non-volatile > register' instruction: > > Snippet from __kthread_create_on_node: > > c000000000136be8: addis r29,r2,-19 > c000000000136bec: ld r29,31424(r29) > if (!__list_add_valid(new, prev, next)) > c000000000136bf0: mr r3,r30 > c000000000136bf4: mr r5,r28 > c000000000136bf8: mr r4,r29 > c000000000136bfc: bl c00000000059a2f8 <__list_add_valid+0x8> > > Register state from WARN_ON(): > > GPR00: c00000000059a3a0 c000007ff23afb50 c000000001344e00 0000000000000075 > GPR04: 0000000000000000 0000000000000000 0000001852af8bc1 0000000000000000 > GPR08: 0000000000000001 0000000000000007 0000000000000006 00000000000004aa > GPR12: 0000000000000000 c000007ffffeb080 c000000000137038 c000005ff62aaa00 > GPR16: 0000000000000000 0000000000000000 c000007fffbe7600 c000007fffbe7370 > GPR20: c000007fffbe7320 c000007fffbe7300 c000000001373a00 0000000000000000 > GPR24: fffffffffffffef7 c00000000012e320 c000007ff23afcb0 c000000000cb8628 > GPR28: c00000000121c8b8 c000000001214e00 c000007fef5b17e8 c000007fef5b17c0 > > Watchpoint hit at 0xc000000000136bec. > > addis r29,r2,-19 > => r29 = 0xc000000001344e00 + (-19 << 16) > => r29 = 0xc000000001214e00 > > ld r29,31424(r29) > => r29 = *(0xc000000001214e00 + 31424) > => r29 = *(0xc00000000121c8c0) > > 0xc00000000121c8c0 is where we placed a watchpoint and thus this > instruction was emulated by emulate_step. But because handle_dabr_fault > did not restore emulated register state, r29 still contains stale > value in above register state. > > Fixes: 5aae8a5370802 ("powerpc, hw_breakpoints: Implement hw_breakpoints for 64-bit server processors") > Signed-off-by: Ravi Bangoria > Cc: stable@vger.kernel.org # 2.6.36+ Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/f474c28fbcbe42faca4eb415172c07d76adcb819 cheers