[PATCH v4 0/5] arm64: Add framework to turn an IPI as NMI

Fri Sep 11 09:28:39 EDT 2020

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