[PATCH 7/7] powerpc/eeh: Add eeh_force_recover to debugfs

[Oliver]

On Fri, Feb 8, 2019 at 11:32 PM Michael Ellerman <mpe at ellerman.id.au> wrote:
>
> Oliver O'Halloran <oohall at gmail.com> writes:
>
> > This patch adds a debugfs interface to force scheduling a recovery event.
> > This can be used to recover a specific PE or schedule a "special" recovery
> > even that checks for errors at the PHB level.
> > To force a recovery of a normal PE, use:
> >
> >  echo '<#pe>:<#phb>' > /sys/kernel/debug/powerpc/eeh_force_recover
> >
> > To force a scan broken PHBs:
> >
> >  echo 'null' > /sys/kernel/debug/powerpc/eeh_force_recover
>
> Why 'null', that seems like an odd choice. Why not "all" or "scan" or
> something?

When an EEH event occurs the bit that is sent to the event handler is
just a pointer the the struct eeh_pe. If the pointer is null it's then
treated as a special event which indicates a PHB failure. I agree it's
a bit dumb, but I don't really expect anyone except me or samb to use
this interface so I went with what would make sense to someone
familiar with the internals.

>
> Also it oopsed on me:
>
> [   76.323164] sending failure event
> [   76.323421] BUG: Unable to handle kernel instruction fetch (NULL pointer?)
> [   76.323655] Faulting instruction address: 0x00000000
> [   76.323856] Oops: Kernel access of bad area, sig: 11 [#1]
> [   76.323946] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> [   76.324295] Modules linked in: vmx_crypto kvm binfmt_misc ip_tables x_tables autofs4 crc32c_vpmsum
> [   76.324669] CPU: 2 PID: 97 Comm: eehd Not tainted 5.0.0-rc2-gcc-8.2.0-00080-gfacc0d1d9517 #435
> [   76.325054] NIP:  0000000000000000 LR: c0000000000451f8 CTR: 0000000000000000
> [   76.325402] REGS: c0000000fec779c0 TRAP: 0400   Not tainted  (5.0.0-rc2-gcc-8.2.0-00080-gfacc0d1d9517)
> [   76.325768] MSR:  800000014280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 24000482  XER: 20000000
> [   76.326243] CFAR: c000000000002528 IRQMASK: 0
> [   76.326243] GPR00: c000000000045edc c0000000fec77c50 c000000001574000 c0000000fec77cb0
> [   76.326243] GPR04: 0000000000000000 00177d76e3e321bc 00177d76e4293a1f 5deadbeef0000100
> [   76.326243] GPR08: 5deadbeef0000200 0000000000000000 0000000000000000 00177d76e3e3216b
> [   76.326243] GPR12: 0000000000000000 c00000003fffdf00 c0000000001438a8 c0000000fe211700
> [   76.326243] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> [   76.326243] GPR20: 0000000000000000 0000000000000000 0000000000000000 c000000000e814e8
> [   76.326243] GPR24: c000000000e814c0 5deadbeef0000100 c000000001622480 0000000100000000
> [   76.326243] GPR28: c000000001413310 c0000000016244e0 c0000000014132f0 c0000001f84246a0
> [   76.329073] NIP [0000000000000000]           (null)
> [   76.329285] LR [c0000000000451f8] eeh_handle_special_event+0x78/0x348
> [   76.329602] Call Trace:
> [   76.329762] [c0000000fec77c50] [c0000000fec77ce0] 0xc0000000fec77ce0 (unreliable)
> [   76.330113] [c0000000fec77d00] [c000000000045edc] eeh_event_handler+0x10c/0x1c0
> [   76.330464] [c0000000fec77db0] [c000000000143a4c] kthread+0x1ac/0x1c0
> [   76.330681] [c0000000fec77e20] [c00000000000bdc4] ret_from_kernel_thread+0x5c/0x78
> [   76.331026] Instruction dump:
> [   76.331197] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
> [   76.331550] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
> [   76.331803] ---[ end trace dc73d37df5bb9ecd ]---
>
>
> cheers

This is probably a side effect of special events being a PowerNV
specific concept. For a pseries guest there should never be any PHB
PEs since (hardware) PHBs are a concept that is hidden to to a guest.
It's like EEH is poorly thought out and full of layering violations or
something...