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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 81E50C433E0 for ; Tue, 11 Aug 2020 13:51:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 51C2E204FD for ; Tue, 11 Aug 2020 13:51:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="F7HWNzuT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728516AbgHKNv3 (ORCPT ); Tue, 11 Aug 2020 09:51:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44796 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728721AbgHKNuo (ORCPT ); Tue, 11 Aug 2020 09:50:44 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E4C8EC061787 for ; Tue, 11 Aug 2020 06:50:39 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id 185so13580853ljj.7 for ; Tue, 11 Aug 2020 06:50:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=i4nkoFmCJzzL1SkDVNUF5LncMf3gqSptzGPM/hRINOw=; b=F7HWNzuTxoTo7n+A7nt9eRcE7ODxZuX8PPec8qjyEnaLtoJ6mTxyC8TkKoh1/Wc2JZ YL9py4gevaJ+/g17NW9EgLePULdGQrxquDHfvpCtkpZZyPZbs9JrB8b5bSwUXciqSc9e C9cCs60raxbZLt4fS0V2khQANzLfsQd231OIz3EkdBiD0Cl4G1YGAa9G3Y0o+abKPyqD oOH1XDgZDb21rxAT3TbRORsYYwF/wLaQkvTiByNcO+TYJmqNehylDdOuziLD0JX/oEtb F/If9/Ia6n+DoU9pO0Bm4nf99MoML1fDjfiS65QKU6qbt0w4QinY0Jmqo8d//1XRWWKu iC1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=i4nkoFmCJzzL1SkDVNUF5LncMf3gqSptzGPM/hRINOw=; b=EJh3AuwSzw4CwFNrjA6F5RkxAl/s5JhSSXlWy0Sy2tBezt7BXT5cc8OIB42IMrp2TO iU2TgKErHE+rcm+5DnV+4/s1+HjbNiC8cpJomsL1QzJ33je3CHSqM4aiIUTQNrMhMrdP 94hkrcMj7eGxJW3X4m63RWy50Y2bU4rRNqnPPkPTM2X4UEQa30lrBQYjWBdW75VMzAid LS9dc0qNKlAdNE+rie9ewO488pKw4wE6C5sAdvko7uYzLGim+6r6nnrvQ381TO6LMUpw ZZuWqivehHtB/QLBReMsQjIh79qrXM2wboAMzZdAyGc/mPvNG5iR12oZTMBZWpN5UETf BBKQ== X-Gm-Message-State: AOAM533BZFgFyhnU7MMPPJpgwVBdQ9G41JaWAbcm3s5Rp+0BkOhteIhw fmuL8D9yNlsypq87h1TJGFMXaEMEeK3YPoSuoIKk2A== X-Google-Smtp-Source: ABdhPJxveGqBC6naFwxbBb/tftPi4ZI9ehibmsHubBYae/7EuAKXoEmf7JSw+kxTu+hUqP/WNud9nUKgzXFLU1zm2sY= X-Received: by 2002:a05:651c:1293:: with SMTP id 19mr2935439ljc.427.1597153837662; Tue, 11 Aug 2020 06:50:37 -0700 (PDT) MIME-Version: 1.0 References: <1595333413-30052-1-git-send-email-sumit.garg@linaro.org> In-Reply-To: <1595333413-30052-1-git-send-email-sumit.garg@linaro.org> From: Sumit Garg Date: Tue, 11 Aug 2020 19:20:26 +0530 Message-ID: Subject: Re: [RFC 0/5] Introduce NMI aware serial drivers To: Greg Kroah-Hartman , Daniel Thompson , Douglas Anderson , linux-serial@vger.kernel.org, kgdb-bugreport@lists.sourceforge.net Cc: Jiri Slaby , Russell King - ARM Linux admin , Jason Wessel , Linux Kernel Mailing List , linux-arm-kernel Content-Type: text/plain; charset="UTF-8" Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Tue, 21 Jul 2020 at 17:40, Sumit Garg wrote: > > Make it possible for UARTs to trigger magic sysrq from an NMI. With the > advent of pseudo NMIs on arm64 it became quite generic to request serial > device interrupt as an NMI rather than IRQ. And having NMI driven serial > RX will allow us to trigger magic sysrq as an NMI and hence drop into > kernel debugger in NMI context. > > The major use-case is to add NMI debugging capabilities to the kernel > in order to debug scenarios such as: > - Primary CPU is stuck in deadlock with interrupts disabled and hence > doesn't honor serial device interrupt. So having magic sysrq triggered > as an NMI is helpful for debugging. > - Always enabled NMI based magic sysrq irrespective of whether the serial > TTY port is active or not. > > Currently there is an existing kgdb NMI serial driver which provides > partial implementation in upstream to have a separate ttyNMI0 port but > that remained in silos with the serial core/drivers which made it a bit > odd to enable using serial device interrupt and hence remained unused. It > seems to be clearly intended to avoid almost all custom NMI changes to > the UART driver. > > But this patch-set allows the serial core/drivers to be NMI aware which > in turn provides NMI debugging capabilities via magic sysrq and hence > there is no specific reason to keep this special driver. So remove it > instead. > > Approach: > --------- > > The overall idea is to intercept serial RX characters in NMI context, if > those are specific to magic sysrq then allow corresponding handler to run > in NMI context. Otherwise, defer all other RX and TX operations onto IRQ > work queue in order to run those in normal interrupt context. > > This approach is demonstrated using amba-pl011 driver. > > Patch-wise description: > ----------------------- > > Patch #1 prepares magic sysrq handler to be NMI aware. > Patch #2 adds NMI framework to serial core. > Patch #3 and #4 demonstrates NMI aware uart port using amba-pl011 driver. > Patch #5 removes kgdb NMI serial driver. > > Goal of this RFC: > ----------------- > > My main reason for sharing this as an RFC is to help decide whether or > not to continue with this approach. The next step for me would to port > the work to a system with an 8250 UART. > A gentle reminder to seek feedback on this series. -Sumit > Usage: > ------ > > This RFC has been developed on top of 5.8-rc3 and if anyone is interested > to give this a try on QEMU, just enable following config options > additional to arm64 defconfig: > > CONFIG_KGDB=y > CONFIG_KGDB_KDB=y > CONFIG_ARM64_PSEUDO_NMI=y > > Qemu command line to test: > > $ qemu-system-aarch64 -nographic -machine virt,gic-version=3 -cpu cortex-a57 \ > -smp 2 -kernel arch/arm64/boot/Image -append 'console=ttyAMA0,38400 \ > keep_bootcon root=/dev/vda2 irqchip.gicv3_pseudo_nmi=1 kgdboc=ttyAMA0' \ > -initrd rootfs-arm64.cpio.gz > > NMI entry into kgdb via sysrq: > - Ctrl a + b + g > > Reference: > ---------- > > For more details about NMI/FIQ debugger, refer to this blog post [1]. > > [1] https://www.linaro.org/blog/debugging-arm-kernels-using-nmifiq/ > > I do look forward to your comments and feedback. > > Sumit Garg (5): > tty/sysrq: Make sysrq handler NMI aware > serial: core: Add framework to allow NMI aware serial drivers > serial: amba-pl011: Re-order APIs definition > serial: amba-pl011: Enable NMI aware uart port > serial: Remove KGDB NMI serial driver > > drivers/tty/serial/Kconfig | 19 -- > drivers/tty/serial/Makefile | 1 - > drivers/tty/serial/amba-pl011.c | 232 +++++++++++++++++------- > drivers/tty/serial/kgdb_nmi.c | 383 --------------------------------------- > drivers/tty/serial/kgdboc.c | 8 - > drivers/tty/serial/serial_core.c | 120 +++++++++++- > drivers/tty/sysrq.c | 33 +++- > include/linux/kgdb.h | 10 - > include/linux/serial_core.h | 67 +++++++ > include/linux/sysrq.h | 1 + > kernel/debug/debug_core.c | 1 + > 11 files changed, 386 insertions(+), 489 deletions(-) > delete mode 100644 drivers/tty/serial/kgdb_nmi.c > > -- > 2.7.4 >