Subject: [Bug 216183] [bisected] Kernel 5.19-rc4 boots ok with CONFIG_PPC_RADIX_MMU=y but fails to boot with CONFIG_PPC_HASH_MMU_NATIVE=y

From: [email-masked]
Date: Thu, 14 Jul 2022 12:57:21 +0000

https://bugzilla.kernel.org/show_bug.cgi?id=216183

--- Comment #8 from Erhard F. ([email-masked]) ---
Created attachment 301425
  --> https://bugzilla.kernel.org/attachment.cgi?id=301425&action=edit
bisect.log

Successfully did a bisect which revealed this commit:

 # git bisect good
a008f8f9fd67ffb13d906ef4ea6235a3d62dfdb6 is the first bad commit
commit a008f8f9fd67ffb13d906ef4ea6235a3d62dfdb6
Author: Nicholas Piggin <[email-masked]>
Date:   Sat Jan 30 23:08:41 2021 +1000

    powerpc/64s/hash: improve context tracking of hash faults

    This moves the 64s/hash context tracking from hash_page_mm() to
    __do_hash_fault(), so it's no longer called by OCXL / SPU
    accelerators, which was certainly the wrong thing to be doing,
    because those callers are not low level interrupt handlers, so
    should have entered a kernel context tracking already.

    Then remain in kernel context for the duration of the fault,
    rather than enter/exit for the hash fault then enter/exit for
    the page fault, which is pointless.

    Even still, calling exception_enter/exit in __do_hash_fault seems
    questionable because that's touching per-cpu variables, tracing,
    etc., which might have been interrupted by this hash fault or
    themselves cause hash faults. But maybe I miss something because
    hash_page_mm very deliberately calls trace_hash_fault too, for
    example. So for now go with it, it's no worse than before, in this
    regard.

    Signed-off-by: Nicholas Piggin <[email-masked]>
    Signed-off-by: Michael Ellerman <[email-masked]>
    Link: https://lore.kernel.org/r/[email-masked]

 arch/powerpc/include/asm/bug.h        |  1 +
 arch/powerpc/mm/book3s64/hash_utils.c |  7 ++++---
 arch/powerpc/mm/fault.c               | 39 +++++++++++++++++++++++++----------
 3 files changed, 33 insertions(+), 14 deletions(-)

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