# Re: \[PATCH v1\] powerpc/64s: Fix unrecoverable MCE crash

- From: Ganesh \<hidden\>
- Date: 2021-09-23 21:37:02 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/09/9524505
- Thread: https://ratatoskr.run/linuxppc-dev/2021/09/9524463/t.md

```text
On 9/22/21 7:32 AM, Nicholas Piggin wrote:

> The machine check handler is not considered NMI on 64s. The early
> handler is the true NMI handler, and then it schedules the
> machine_check_exception handler to run when interrupts are enabled.
>
> This works fine except the case of an unrecoverable MCE, where the true
> NMI is taken when MSR[RI] is clear, it can not recover to schedule the
> next handler, so it calls machine_check_exception directly so something
> might be done about it.
>
> Calling an async handler from NMI context can result in irq state and
> other things getting corrupted. This can also trigger the BUG at
> arch/powerpc/include/asm/interrupt.h:168.
>
> Fix this by just making the 64s machine_check_exception handler an NMI
> like it is on other subarchs.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---

Hi Nick,

If I inject control memory access error in LPAR on top of this patch
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210906084303.183921-1-ganeshgr@linux.ibm.com/

I see the following warning trace

WARNING: CPU: 130 PID: 7122 at arch/powerpc/include/asm/interrupt.h:319 machine_check_exception+0x310/0x340
 Modules linked in:
 CPU: 130 PID: 7122 Comm: inj_access_err Kdump: loaded Tainted: G   M              5.15.0-rc2-cma-00054-g4a0d59fbaf71-dirty #22
 NIP:  c00000000002f980 LR: c00000000002f7e8 CTR: c000000000a31860
 REGS: c0000039fe51bb20 TRAP: 0700   Tainted: G   M               (5.15.0-rc2-cma-00054-g4a0d59fbaf71-dirty)
 MSR:  8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 88000222  XER: 20040000
 CFAR: c00000000002f844 IRQMASK: 0
 GPR00: c00000000002f798 c0000039fe51bdc0 c0000000020d0000 0000000000000001
 GPR04: 0000000000000000 4000000000000002 4000000000000000 00000000000019af
 GPR08: 00000077e5ad0000 0000000000000000 c0000077ee16c700 0000000000000080
 GPR12: 0000000088000222 c0000077ee16c700 0000000000000000 0000000000000000
 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR24: 0000000000000000 0000000000000000 c0000000020fecd8 0000000000000000
 GPR28: 0000000000000000 0000000000000001 0000000000000001 c0000039fe51be80
 NIP [c00000000002f980] machine_check_exception+0x310/0x340
 LR [c00000000002f7e8] machine_check_exception+0x178/0x340
 Call Trace:
 [c0000039fe51bdc0] [c00000000002f798] machine_check_exception+0x128/0x340 (unreliable)
 [c0000039fe51be10] [c0000000000086ec] machine_check_common+0x1ac/0x1b0
 --- interrupt: 200 at 0x10000968
 NIP:  0000000010000968 LR: 0000000010000958 CTR: 0000000000000000
 REGS: c0000039fe51be80 TRAP: 0200   Tainted: G   M               (5.15.0-rc2-cma-00054-g4a0d59fbaf71-dirty)
 MSR:  8000000002a0f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 22000824  XER: 00000000
 CFAR: 000000000000021c DAR: 00007fffb00c0000 DSISR: 02000008 IRQMASK: 0
 GPR00: 0000000022000824 00007fffc9647770 0000000010027f00 00007fffb00c0000
 GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR08: 0000000000000000 00007fffb00c0000 0000000000000001 0000000000000000
 GPR12: 0000000000000000 00007fffb015a330 0000000000000000 0000000000000000
 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 GPR24: 0000000000000000 0000000000000000 0000000000000000 000000001000085c
 GPR28: 00007fffc9647d18 0000000000000001 00000000100009b0 00007fffc9647770
 NIP [0000000010000968] 0x10000968
 LR [0000000010000958] 0x10000958
 --- interrupt: 200

```