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 B27A4C433EF for ; Sat, 14 May 2022 02:54:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230217AbiENCyu (ORCPT ); Fri, 13 May 2022 22:54:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55722 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230484AbiENCyk (ORCPT ); Fri, 13 May 2022 22:54:40 -0400 X-Greylist: delayed 5901 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Fri, 13 May 2022 18:11:27 PDT Received: from outgoing-stata.csail.mit.edu (outgoing-stata.csail.mit.edu [128.30.2.210]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6591E37B8CB for ; Fri, 13 May 2022 18:11:27 -0700 (PDT) Received: from [128.177.82.146] (helo=srivatsab-a02.vmware.com) by outgoing-stata.csail.mit.edu with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1npemM-000Vex-0L; Fri, 13 May 2022 19:33:02 -0400 To: Elliot Berman , Juergen Gross , Alexey Makhalov , Catalin Marinas , Will Deacon Cc: Prakruthi Deepak Heragu , virtualization@lists.linux-foundation.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Murali Nalajala References: <20220513174654.362169-1-quic_eberman@quicinc.com> From: "Srivatsa S. Bhat" Subject: Re: [PATCH v3] arm64: paravirt: Use RCU read locks to guard stolen_time Message-ID: Date: Fri, 13 May 2022 16:32:53 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20220513174654.362169-1-quic_eberman@quicinc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/13/22 10:46 AM, Elliot Berman wrote: > From: Prakruthi Deepak Heragu > > During hotplug, the stolen time data structure is unmapped and memset. > There is a possibility of the timer IRQ being triggered before memset > and stolen time is getting updated as part of this timer IRQ handler. This > causes the below crash in timer handler - > > [ 3457.473139][ C5] Unable to handle kernel paging request at virtual address ffffffc03df05148 > ... > [ 3458.154398][ C5] Call trace: > [ 3458.157648][ C5] para_steal_clock+0x30/0x50 > [ 3458.162319][ C5] irqtime_account_process_tick+0x30/0x194 > [ 3458.168148][ C5] account_process_tick+0x3c/0x280 > [ 3458.173274][ C5] update_process_times+0x5c/0xf4 > [ 3458.178311][ C5] tick_sched_timer+0x180/0x384 > [ 3458.183164][ C5] __run_hrtimer+0x160/0x57c > [ 3458.187744][ C5] hrtimer_interrupt+0x258/0x684 > [ 3458.192698][ C5] arch_timer_handler_virt+0x5c/0xa0 > [ 3458.198002][ C5] handle_percpu_devid_irq+0xdc/0x414 > [ 3458.203385][ C5] handle_domain_irq+0xa8/0x168 > [ 3458.208241][ C5] gic_handle_irq.34493+0x54/0x244 > [ 3458.213359][ C5] call_on_irq_stack+0x40/0x70 > [ 3458.218125][ C5] do_interrupt_handler+0x60/0x9c > [ 3458.223156][ C5] el1_interrupt+0x34/0x64 > [ 3458.227560][ C5] el1h_64_irq_handler+0x1c/0x2c > [ 3458.232503][ C5] el1h_64_irq+0x7c/0x80 > [ 3458.236736][ C5] free_vmap_area_noflush+0x108/0x39c > [ 3458.242126][ C5] remove_vm_area+0xbc/0x118 > [ 3458.246714][ C5] vm_remove_mappings+0x48/0x2a4 > [ 3458.251656][ C5] __vunmap+0x154/0x278 > [ 3458.255796][ C5] stolen_time_cpu_down_prepare+0xc0/0xd8 > [ 3458.261542][ C5] cpuhp_invoke_callback+0x248/0xc34 > [ 3458.266842][ C5] cpuhp_thread_fun+0x1c4/0x248 > [ 3458.271696][ C5] smpboot_thread_fn+0x1b0/0x400 > [ 3458.276638][ C5] kthread+0x17c/0x1e0 > [ 3458.280691][ C5] ret_from_fork+0x10/0x20 > > As a fix, introduce rcu lock to update stolen time structure. > > Suggested-by: Will Deacon > Signed-off-by: Prakruthi Deepak Heragu > Signed-off-by: Elliot Berman > --- Looks good to me, but one quick question though (see below). Reviewed-by: Srivatsa S. Bhat (VMware) > > static int stolen_time_cpu_down_prepare(unsigned int cpu) > { > + struct pvclock_vcpu_stolen_time *kaddr = NULL; > struct pv_time_stolen_time_region *reg; > > reg = this_cpu_ptr(&stolen_time_region); > if (!reg->kaddr) > return 0; > > - memunmap(reg->kaddr); > - memset(reg, 0, sizeof(*reg)); > + kaddr = rcu_replace_pointer(reg->kaddr, NULL, true); > + synchronize_rcu(); > + memunmap(kaddr); > The original code used to memset the stolen time region, but this patch seems to drop it. Was that change intentional? Regards, Srivatsa