[RFC Patch v1 0/4] arm64: Introduce new IPI as IPI_CALL_NMI_FUNC

[Sumit Garg]

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 kgdb relies on NMI support to round up CPUs which are stuck in
hard lockup state with interrupts disabled.

This patch-set adds support for IPI_CALL_NMI_FUNC which can be triggered
as a pseudo NMI which in turn is leveraged via kgdb to round up CPUs.

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

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

# Enter kdb via Magic SysRq

[11]kdb> btc
btc: cpu status: Currently on cpu 11
Available cpus: 0-10(I), 11, 12(I), 13, 14-23(I)
<snip>
Stack traceback for pid 623
0xffff00086a644600      623      622  1   13   R  0xffff00086a644fc0  bash
CPU: 13 PID: 623 Comm: bash Not tainted 5.7.0-rc2 #27
Hardware name: Socionext SynQuacer E-series DeveloperBox, BIOS build #73 Apr  6 2020
Call trace:
 dump_backtrace+0x0/0x198
 show_stack+0x18/0x28
 dump_stack+0xb8/0x100
 kgdb_cpu_enter+0x5c0/0x5f8
 kgdb_nmicallback+0xa0/0xa8
 handle_IPI+0x190/0x200
 gic_handle_irq+0x2b8/0x2d8
 el1_irq+0xcc/0x180
 lkdtm_HARDLOCKUP+0x8/0x18
 direct_entry+0x124/0x1c0
 full_proxy_write+0x60/0xb0
 __vfs_write+0x1c/0x48
 vfs_write+0xe4/0x1d0
 ksys_write+0x6c/0xf8
 __arm64_sys_write+0x1c/0x28
 el0_svc_common.constprop.0+0x74/0x1f0
 do_el0_svc+0x24/0x90
 el0_sync_handler+0x178/0x2b8
 el0_sync+0x158/0x180
<snip>

Looking forward to your comments/feedback.

Sumit Garg (4):
  arm64: smp: Introduce a new IPI as IPI_CALL_NMI_FUNC
  irqchip/gic-v3: Add support to handle SGI as pseudo NMI
  irqchip/gic-v3: Enable arch specific IPI as pseudo NMI
  arm64: kgdb: Round up cpus using IPI_CALL_NMI_FUNC

 arch/arm64/include/asm/hardirq.h |  2 +-
 arch/arm64/include/asm/smp.h     |  1 +
 arch/arm64/kernel/kgdb.c         | 15 +++++++++++++++
 arch/arm64/kernel/smp.c          | 36 +++++++++++++++++++++++++++++++++++-
 drivers/irqchip/irq-gic-v3.c     | 36 +++++++++++++++++++++++++++++++-----
 5 files changed, 83 insertions(+), 7 deletions(-)

-- 
2.7.4