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 CA1C2ECAAA3 for ; Fri, 26 Aug 2022 03:27:02 +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: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=cW5uhI+PEcGYfsGSM8YdkbJxxs4INZz5wP0p3wftD/Q=; b=GF+cBuhhCiv++VdjRGVyEQN0Cr 70XzssNmCH2kfM2yyni0C0FYbxUOfqxS5wrqDX8iMvroSWFiHskmSp9l4ZMF4cNnaKoK3AVIeewou ayWlNx5suR3Ssubo4sbmd0hiP3Do3Gte27numND/9VFO/P+Og2ePOZr8z1j6jUzYnV+X/r5EdZhTT ecCAHrZAi7eSXSyiWw7Cv9K0Sy9nasFZehaRWDos99miRyatIR36bXH7xDGj2lNwTcrq6P0FTddjp 9rFSEqVuhcNDJvrzXdsjIFD5blybJ+yOS+BChtCoXxYpVoMEST8gDmZwbN70b7G3ouOY3G6nNta2u L16l9WHQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oRPyg-008DAv-No; Fri, 26 Aug 2022 03:25:50 +0000 Received: from szxga08-in.huawei.com ([45.249.212.255]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oRPyc-008C6p-TO for linux-arm-kernel@lists.infradead.org; Fri, 26 Aug 2022 03:25:49 +0000 Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4MDQ9r3GR0z1N7MS; Fri, 26 Aug 2022 11:22:08 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 26 Aug 2022 11:25:40 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 26 Aug 2022 11:25:40 +0800 Subject: Re: [PATCH 1/2] arm64/traps: Replace this_cpu_* with raw_cpu_* in panic_bad_stack() To: Mark Rutland CC: Catalin Marinas , Will Deacon , Russell King , , , References: <20220825063154.69-1-thunder.leizhen@huawei.com> <20220825063154.69-2-thunder.leizhen@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <569fd51d-aca2-f1c0-d90e-2ae34e4f6f99@huawei.com> Date: Fri, 26 Aug 2022 11:25:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220825_202547_320722_FC30E8A0 X-CRM114-Status: GOOD ( 23.51 ) 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 2022/8/25 21:29, Mark Rutland wrote: > On Thu, Aug 25, 2022 at 02:31:53PM +0800, Zhen Lei wrote: >> The hardware automatically disable the IRQ interrupt before jumping to the >> interrupt or exception vector. Therefore, the preempt_disable() operation >> in this_cpu_read() after macro expansion is unnecessary. In fact, before >> commit 8168f098867f ("arm64: entry: split bad stack entry"), the operation >> this_cpu_read() precedes arm64_enter_nmi(). If set_preempt_need_resched() >> is called before stack overflow, this_cpu_read() may trigger scheduling, >> see pseudocode below. >> >> Pseudocode of this_cpu_read(xx) when CONFIG_PREEMPTION=y: >> preempt_disable_notrace(); >> raw_cpu_read(xx); >> if (unlikely(__preempt_count_dec_and_test())) >> __preempt_schedule_notrace(); > > Ok, but in mainline we have commit 8168f098867f; so we cannot reach here > without having fiddled with the preempt count. > > Are you saying that some stable kernel is broken because it lacks commit > 8168f098867f? Is so, I think the right fix is to backport commit 8168f098867f, > and that is then irrelevant to this change. Yes, after backport commit 8168f098867f, the risk is gone. > >> Therefore, use raw_cpu_* instead of this_cpu_* to eliminate potential >> hazards. At the very least, it reduces a few lines of assembly code. > > I'm happy to use raw_cpu_*() here, to minimize the work we have to do, any any > risks with e.g. instrumentation, but as above I don't think the case mentioned > in the commit message is relevant. OK, I will delete the description about risk. > > Thanks, > Mark. > >> >> Signed-off-by: Zhen Lei >> --- >> arch/arm64/kernel/traps.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c >> index b7fed33981f7b76..e6b6f4650e3d895 100644 >> --- a/arch/arm64/kernel/traps.c >> +++ b/arch/arm64/kernel/traps.c >> @@ -871,8 +871,8 @@ DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack) >> void panic_bad_stack(struct pt_regs *regs, unsigned long esr, unsigned long far) >> { >> unsigned long tsk_stk = (unsigned long)current->stack; >> - unsigned long irq_stk = (unsigned long)this_cpu_read(irq_stack_ptr); >> - unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack); >> + unsigned long irq_stk = (unsigned long)raw_cpu_read(irq_stack_ptr); >> + unsigned long ovf_stk = (unsigned long)raw_cpu_ptr(overflow_stack); >> >> console_verbose(); >> pr_emerg("Insufficient stack space to handle exception!"); >> -- >> 2.25.1 >> > . > -- Regards, Zhen Lei _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel