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    SubjectRe: [PATCH v2 4/4] arm64: acpi: fix alignment fault in accessing ACPI
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    Hi Akashi,

    On 19/06/18 07:44, AKASHI Takahiro wrote:
    > This is a fix against the issue that crash dump kernel may hang up
    > during booting, which can happen on any ACPI-based system with "ACPI
    > Reclaim Memory."
    >
    > (kernel messages after panic kicked off kdump)
    > (snip...)
    > Bye!
    > (snip...)
    > ACPI: Core revision 20170728
    > pud=000000002e7d0003, *pmd=000000002e7c0003, *pte=00e8000039710707
    > Internal error: Oops: 96000021 [#1] SMP
    > Modules linked in:
    > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc6 #1
    > task: ffff000008d05180 task.stack: ffff000008cc0000
    > PC is at acpi_ns_lookup+0x25c/0x3c0
    > LR is at acpi_ds_load1_begin_op+0xa4/0x294
    > (snip...)
    > Process swapper/0 (pid: 0, stack limit = 0xffff000008cc0000)
    > Call trace:
    > (snip...)
    > [<ffff0000084a6764>] acpi_ns_lookup+0x25c/0x3c0
    > [<ffff00000849b4f8>] acpi_ds_load1_begin_op+0xa4/0x294
    > [<ffff0000084ad4ac>] acpi_ps_build_named_op+0xc4/0x198
    > [<ffff0000084ad6cc>] acpi_ps_create_op+0x14c/0x270
    > [<ffff0000084acfa8>] acpi_ps_parse_loop+0x188/0x5c8
    > [<ffff0000084ae048>] acpi_ps_parse_aml+0xb0/0x2b8
    > [<ffff0000084a8e10>] acpi_ns_one_complete_parse+0x144/0x184
    > [<ffff0000084a8e98>] acpi_ns_parse_table+0x48/0x68
    > [<ffff0000084a82cc>] acpi_ns_load_table+0x4c/0xdc
    > [<ffff0000084b32f8>] acpi_tb_load_namespace+0xe4/0x264
    > [<ffff000008baf9b4>] acpi_load_tables+0x48/0xc0
    > [<ffff000008badc20>] acpi_early_init+0x9c/0xd0
    > [<ffff000008b70d50>] start_kernel+0x3b4/0x43c
    > Code: b9008fb9 2a000318 36380054 32190318 (b94002c0)
    > ---[ end trace c46ed37f9651c58e ]---
    > Kernel panic - not syncing: Fatal exception
    > Rebooting in 10 seconds..
    >
    > (diagnosis)
    > * This fault is a data abort, alignment fault (ESR=0x96000021)
    > during reading out ACPI table.
    > * Initial ACPI tables are normally stored in system ram and marked as
    > "ACPI Reclaim memory" by the firmware.
    > * After the commit f56ab9a5b73c ("efi/arm: Don't mark ACPI reclaim
    > memory as MEMBLOCK_NOMAP"), those regions are differently handled
    > as they are "memblock-reserved", without NOMAP bit.
    > * So they are now excluded from device tree's "usable-memory-range"
    > which kexec-tools determines based on a current view of /proc/iomem.
    > * When crash dump kernel boots up, it tries to accesses ACPI tables by
    > mapping them with ioremap(), not ioremap_cache(), in acpi_os_ioremap()
    > since they are no longer part of mapped system ram.
    > * Given that ACPI accessor/helper functions are compiled in without
    > unaligned access support (ACPI_MISALIGNMENT_NOT_SUPPORTED),
    > any unaligned access to ACPI tables can cause a fatal panic.
    >
    > With this patch, acpi_os_ioremap() always honors memory attribute
    > information provided by the firmware (EFI) and retaining cacheability
    > allows the kernel safe access to ACPI tables.

    Reviewed-by: James Morse <james.morse@arm.com>


    Thanks,

    James

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