Message-Id: <1599830924-13990-1-git-send-email-sumit.garg@linaro.org>
Date:   Fri, 11 Sep 2020 18:58:39 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     maz@...nel.org, catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        jason@...edaemon.net, mark.rutland@....com,
        julien.thierry.kdev@...il.com, dianders@...omium.org,
        daniel.thompson@...aro.org, jason.wessel@...driver.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH v4 0/5] arm64: Add framework to turn an IPI as NMI

With pseudo NMIs support available its possible to configure SGIs to be
triggered as pseudo NMIs running in NMI context. And kernel features
such as:
- NMI backtrace can leverage IPI turned as NMI to get a backtrace of CPU
  stuck in hard lockup using magic SYSRQ.
- kgdb relies on NMI support to round up CPUs which are stuck in hard
  lockup state with interrupts disabled.

This patch-set adds framework to turn an IPI as NMI which can be triggered
as a pseudo NMI which in turn invokes registered NMI handlers.

After this patch-set we should be able to get a backtrace for a CPU
stuck in HARDLOCKUP. Have a look at an examples below from a hard lockup
testcase run on Developerbox:

$ echo HARDLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT

NMI backtrace:
==============

# Issue Magic SysRq to dump backtrace

[  376.894502] NMI backtrace for cpu 8
[  376.894506] CPU: 8 PID: 555 Comm: bash Not tainted 5.9.0-rc3-00740-g06ff047-dirty #242
[  376.894510] Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #73 Apr  6 2020
[  376.894514] pstate: 40000005 (nZcv daif -PAN -UAO BTYPE=--)
[  376.894517] pc : lkdtm_HARDLOCKUP+0x8/0x18
[  376.894520] lr : lkdtm_do_action+0x24/0x30
[  376.894524] sp : ffff800012cebd20
[  376.894527] pmr_save: 00000060
[  376.894530] x29: ffff800012cebd20 x28: ffff000875ae8000 
[  376.894540] x27: 0000000000000000 x26: 0000000000000000 
[  376.894550] x25: 000000000000001a x24: ffff800012cebe40 
[  376.894560] x23: 000000000000000b x22: ffff800010fc5040 
[  376.894569] x21: ffff000878b61000 x20: ffff8000113b2870 
[  376.894579] x19: 000000000000001b x18: 0000000000000010 
[  376.894588] x17: 0000000000000000 x16: 0000000000000000 
[  376.894598] x15: ffff000875ae8470 x14: 00000000000002ad 
[  376.894613] x13: 0000000000000000 x12: 0000000000000000 
[  376.894622] x11: 0000000000000007 x10: 00000000000009c0 
[  376.894631] x9 : ffff800012ceba80 x8 : ffff000875ae8a20 
[  376.894641] x7 : ffff00087f6b3280 x6 : ffff00087f6b3200 
[  376.894651] x5 : 0000000000000000 x4 : ffff00087f6a91f8 
[  376.894660] x3 : ffff00087f6b0120 x2 : 1aa310cec69eb500 
[  376.894670] x1 : 0000000000000000 x0 : 0000000000000060 
[  376.894679] Call trace:
[  376.894683]  lkdtm_HARDLOCKUP+0x8/0x18
[  376.894686]  direct_entry+0x124/0x1c0
[  376.894689]  full_proxy_write+0x60/0xb0
[  376.894693]  vfs_write+0xf0/0x230
[  376.894696]  ksys_write+0x6c/0xf8
[  376.894699]  __arm64_sys_write+0x1c/0x28
[  376.894703]  el0_svc_common.constprop.0+0x74/0x1f0
[  376.894707]  do_el0_svc+0x24/0x90
[  376.894710]  el0_sync_handler+0x180/0x2f8
[  376.894713]  el0_sync+0x158/0x180

KGDB:
=====

# Enter kdb via Magic SysRq

[6]kdb> btc
btc: cpu status: Currently on cpu 6
Available cpus: 0-5(I), 6, 7(I), 8, 9-23(I)
<snip>
Stack traceback for pid 555
0xffff000875ae8000      555      554  1    8   R  0xffff000875ae89c0  bash
CPU: 8 PID: 555 Comm: bash Not tainted 5.9.0-rc3-00740-g06ff047-dirty #242
Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #73 Apr  6 2020
Call trace:
 dump_backtrace+0x0/0x1a0
 show_stack+0x18/0x28
 dump_stack+0xc0/0x11c
 kgdb_cpu_enter+0x648/0x660
 kgdb_nmicallback+0xa0/0xa8
 ipi_kgdb_nmicallback+0x24/0x30
 ipi_nmi_handler+0x48/0x60
 handle_percpu_devid_fasteoi_ipi+0x74/0x88
 generic_handle_irq+0x30/0x48
 handle_domain_nmi+0x48/0x80
 gic_handle_irq+0x18c/0x34c
 el1_irq+0xcc/0x180
 lkdtm_HARDLOCKUP+0x8/0x18
 direct_entry+0x124/0x1c0
 full_proxy_write+0x60/0xb0
 vfs_write+0xf0/0x230
 ksys_write+0x6c/0xf8
 __arm64_sys_write+0x1c/0x28
 el0_svc_common.constprop.0+0x74/0x1f0
 do_el0_svc+0x24/0x90
 el0_sync_handler+0x180/0x2f8
 el0_sync+0x158/0x180
<snip>

Changes in v4:
- Move IPI NMI framework to a separate file.
- Get rid of hard-coded IPI_CALL_NMI_FUNC allocation.
- Add NMI backtrace support leveraged via magic SYSRQ.

Changes in v3:
- Rebased to Marc's latest IPIs patch-set [1].

[1] https://lkml.org/lkml/2020/9/1/603

Changes since RFC version [1]:
- Switch to use generic interrupt framework to turn an IPI as NMI.
- Dependent on Marc's patch-set [2] which turns IPIs into normal
  interrupts.
- Addressed misc. comments from Doug on patch #4.
- Posted kgdb NMI printk() fixup separately which has evolved since
  to be solved using different approach via changing kgdb interception
  of printk() in common printk() code (see patch [3]).

[1] https://lkml.org/lkml/2020/4/24/328
[2] https://lkml.org/lkml/2020/5/19/710
[3] https://lkml.org/lkml/2020/5/20/418

Sumit Garg (5):
  arm64: Add framework to turn IPI as NMI
  irqchip/gic-v3: Enable support for SGIs to act as NMIs
  arm64: smp: Allocate and setup IPI as NMI
  arm64: kgdb: Round up cpus using IPI as NMI
  arm64: ipi_nmi: Add support for NMI backtrace

 arch/arm64/include/asm/irq.h  |  6 +++
 arch/arm64/include/asm/kgdb.h |  8 ++++
 arch/arm64/include/asm/nmi.h  | 16 ++++++++
 arch/arm64/kernel/Makefile    |  2 +-
 arch/arm64/kernel/ipi_nmi.c   | 93 +++++++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/kgdb.c      | 21 ++++++++++
 arch/arm64/kernel/smp.c       |  8 ++++
 drivers/irqchip/irq-gic-v3.c  | 13 +++++-
 8 files changed, 164 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/nmi.h
 create mode 100644 arch/arm64/kernel/ipi_nmi.c

-- 
2.7.4

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