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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 894CAC433C1 for ; Tue, 23 Mar 2021 12:41:21 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 2300E619A5 for ; Tue, 23 Mar 2021 12:41:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2300E619A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=w8j6zcj4ajNAZJCpg6zH+hh+47e+qwixeQXkBeK+CYo=; b=GNLXqpNDxTihKggoVVoNYghWI Ca4/w5QVeDk61YhK/vI1YHrumRFokiZAvoVt9bIWhgmPiBiHMYruWOOkzLk8MGDXNUX8r1rn2hRAx UaL8r32wMcNaPHAaHoD3uVGCwQh99CC97vG3oo/L3gdelgCSJDYSGB4jSE1AGKyzyP2W+l9koUzfZ yDdrESK0veCNvlD98Foc6kQie24ndY19o2t3eJwrgjGBZd6SxJKDMBWUTNd7hfGC7znerkgocEj0Q fE2CtDuzZUI8Wzb12zFr/294ze3JMqwUdjPZX5c0DxIDIXo/8bwqvDMjE9ICjWpYqk+AWTxuYnnZl w8UGe0oGA==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lOgJy-00EyRn-H5; Tue, 23 Mar 2021 12:39:42 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lOgJv-00EyRK-0U for linux-arm-kernel@lists.infradead.org; Tue, 23 Mar 2021 12:39:41 +0000 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id D9A1C20B5680; Tue, 23 Mar 2021 05:39:34 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com D9A1C20B5680 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1616503175; bh=ZM1TUjVtcj9fUDxiWHRBdCZdKbGib/ZLyhytDZGLoSg=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=h1zZOGQa1/jrejGFm5sp1vGyLjxQd/+bfF66G3dbpiTELhRdYlGmmXRsPeC6rR7Y4 vZGmX9wPMMjOYWjiRGW2m1pO3sJtTmhBGkaDkfRrTLZ/s6bN2dgy9MGeoLV3Iehrtl c4/5MQ35KyuHvvBnfqnJyHW5keQVecsQJNqwa3UU= Subject: Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record To: Mark Rutland Cc: Mark Brown , jpoimboe@redhat.com, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <5997dfe8d261a3a543667b83c902883c1e4bd270> <20210315165800.5948-1-madvenka@linux.microsoft.com> <20210315165800.5948-2-madvenka@linux.microsoft.com> <20210318150905.GL5469@sirena.org.uk> <8591e34a-c181-f3ff-e691-a6350225e5b4@linux.microsoft.com> <20210319123023.GC5619@sirena.org.uk> <5dbaf34f-b2fc-b9b8-3918-83356f2f752a@linux.microsoft.com> <6e3ac22b-99b8-7d99-59bd-6a2d1158b3c9@linux.microsoft.com> <254ed4a1-8342-d879-2fbc-3933118df949@linux.microsoft.com> <20210323102339.GA95840@C02TD0UTHF1T.local> From: "Madhavan T. Venkataraman" Message-ID: Date: Tue, 23 Mar 2021 07:39:34 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210323102339.GA95840@C02TD0UTHF1T.local> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210323_123939_483274_E75C8BE7 X-CRM114-Status: GOOD ( 29.90 ) 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 3/23/21 5:24 AM, Mark Rutland wrote: > On Fri, Mar 19, 2021 at 05:03:09PM -0500, Madhavan T. Venkataraman wrote: >> I solved this by using existing functions logically instead of inventing a >> dummy function. I initialize pt_regs->stackframe[1] to an existing function >> so that the stack trace will not show a 0x0 entry as well as the kernel and >> gdb will show identical stack traces. >> >> For all task stack traces including the idle tasks, the stack trace will >> end at copy_thread() as copy_thread() is the function that initializes the >> pt_regs and the first stack frame for a task. > > I don't think this is a good idea, as it will mean that copy_thread() > will appear to be live in every thread, and therefore will not be > patchable. > > There are other things people need to be aware of when using an external > debugger (e.g. during EL0<->ELx transitions there are periods when X29 > and X30 contain the EL0 values, and cannot be used to unwind), so I > don't think there's a strong need to make this look prettier to an > external debugger. > OK. >> For EL0 exceptions, the stack trace will end with vectors() as vectors >> entries call the EL0 handlers. >> >> Here are sample stack traces (I only show the ending of each trace): >> >> Idle task on primary CPU >> ======================== >> >> ... >> [ 0.022557] start_kernel+0x5b8/0x5f4 >> [ 0.022570] __primary_switched+0xa8/0xb8 >> [ 0.022578] copy_thread+0x0/0x188 >> >> Idle task on secondary CPU >> ========================== >> >> ... >> [ 0.023397] secondary_start_kernel+0x188/0x1e0 >> [ 0.023406] __secondary_switched+0x40/0x88 >> [ 0.023415] copy_thread+0x0/0x188 >> >> All other kernel threads >> ======================== >> >> ... >> [ 13.501062] ret_from_fork+0x10/0x18 >> [ 13.507998] copy_thread+0x0/0x188 >> >> User threads (EL0 exception) >> ============ >> >> write(2) system call example: >> >> ... >> [ 521.686148] vfs_write+0xc8/0x2c0 >> [ 521.686156] ksys_write+0x74/0x108 >> [ 521.686161] __arm64_sys_write+0x24/0x30 >> [ 521.686166] el0_svc_common.constprop.0+0x70/0x1a8 >> [ 521.686175] do_el0_svc+0x2c/0x98 >> [ 521.686180] el0_svc+0x2c/0x70 >> [ 521.686188] el0_sync_handler+0xb0/0xb8 >> [ 521.686193] el0_sync+0x17c/0x180 >> [ 521.686198] vectors+0x0/0x7d8 > > [...] > >> If you approve, the above will become RFC Patch v3 1/8 in the next version. > > As above, I don't think we should repurpose an existing function here, > and my preference is to use 0x0. > OK. >> Let me know. >> >> Also, I could introduce an extra frame in the EL1 exception stack trace that >> includes vectors so the stack trace would look like this (timer interrupt example): >> >> call_timer_fn >> run_timer_softirq >> __do_softirq >> irq_exit >> __handle_domain_irq >> gic_handle_irq >> el1_irq >> vectors >> >> This way, if the unwinder finds vectors, it knows that it is an exception frame. > > I can see this might make it simpler to detect exception boundaries, but > I suspect that we need other information anyway, so this doesn't become > all that helpful. For EL0<->EL1 exception boundaries we want to > successfully terminate a robust stacktrace whereas for EL1<->EL1 > exception boundaries we want to fail a robust stacktrace. > > I reckon we have to figure that out from the el1_* and el0_* entry > points (which I am working to reduce/simplify as part of the entry > assembly conversion to C). With that we can terminate unwind at the > el0_* parts, and reject unwinding across any other bit of .entry.text. > OK. That is fine. Thanks. Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel