[PATCH] arm64: kdump: retain reserved memory regions

[Ard Biesheuvel]

On 10 January 2018 at 10:09, AKASHI Takahiro <takahiro.akashi at linaro.org> 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."
>
>         <kicking off kdump after panic>
>         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' attribute were changed
>   removing NOMAP bit and they are instead "memblock-reserved".
> * When crash dump kernel boots up, it tries to accesses ACPI tables by
>   ioremap'ing them (through acpi_os_ioremap()).
> * Since those regions are not included in device tree's
>   "usable-memory-range" and so not recognized as part of crash dump
>   kernel's system ram, ioremap() will create a non-cacheable mapping here.
> * ACPI accessor/helper functions are compiled in without unaligned access
>   support (ACPI_MISALIGNMENT_NOT_SUPPORTED), eventually ending up a fatal
>   panic when accessing ACPI tables.
>
> With this patch, all the reserved memory regions, as well as NOMAP-
> attributed ones which are presumably ACPI runtime code and data, are set
> to be retained in system ram even if they are outside of usable memory
> range specified by device tree blob. Accordingly, ACPI tables are mapped
> as cacheable and can be safely accessed without causing unaligned access
> faults.
>
> Reported-by: Bhupesh Sharma <bhsharma at redhat.com>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
>  arch/arm64/mm/init.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 2d5a443b205c..e4a8b64a09b1 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -352,11 +352,23 @@ static void __init fdt_enforce_memory_region(void)
>         struct memblock_region reg = {
>                 .size = 0,
>         };
> +       u64 idx;
> +       phys_addr_t start, end;
>
>         of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
>
> -       if (reg.size)
> -               memblock_cap_memory_range(reg.base, reg.size);

Given that memblock_cap_memory_range() was introduced by you for
kdump, is there any way to handle it there?
If not, should we remove it?

> +       if (reg.size) {
> +retry:
> +               /* exclude usable & !reserved memory */
> +               for_each_free_mem_range(idx, NUMA_NO_NODE, MEMBLOCK_NONE,
> +                                       &start, &end, NULL) {
> +                       memblock_remove(start, end - start);
> +                       goto retry;
> +               }
> +
> +               /* add back fdt's usable memory */
> +               memblock_add(reg.base, reg.size);
> +       }
>  }
>
>  void __init arm64_memblock_init(void)
> --
> 2.15.1
>