When booting an ACPI enabled kernel with 'mem=x', there is the
possibility that ACPI data regions from the firmware will lie above the
memory limit.  Ordinarily these will be removed by
memblock_enforce_memory_limit(.).

Unfortunately, this means that these regions will then be mapped by
acpi_os_ioremap(.) as device memory (instead of normal) thus unaligned
accessess will then provoke alignment faults.

In this patch we adopt memblock_mem_limit_remove_map instead, and this
preserves these ACPI data regions (marked NOMAP) thus ensuring that
these regions are not mapped as device memory.

For example, below is an alignment exception observed on ARM platform
when booting the kernel with 'acpi=on mem=8G':

  ...
  Unable to handle kernel paging request at virtual address ffff0000080521e7
  pgd = ffff000008aa0000
  [ffff0000080521e7] *pgd=000000801fffe003, *pud=000000801fffd003, *pmd=000000801fffc003, *pte=00e80083ff1c1707
  Internal error: Oops: 96000021 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc3-next-20160616+ #172
  Hardware name: AMD Overdrive/Supercharger/Default string, BIOS ROD1001A 02/09/2016
  task: ffff800001ef0000 ti: ffff800001ef8000 task.ti: ffff800001ef8000
  PC is at acpi_ns_lookup+0x520/0x734
  LR is at acpi_ns_lookup+0x4a4/0x734
  pc : [<ffff0000083b8b10>] lr : [<ffff0000083b8a94>] pstate: 60000045
  sp : ffff800001efb8b0
  x29: ffff800001efb8c0 x28: 000000000000001b
  x27: 0000000000000001 x26: 0000000000000000
  x25: ffff800001efb9e8 x24: ffff000008a10000
  x23: 0000000000000001 x22: 0000000000000001
  x21: ffff000008724000 x20: 000000000000001b
  x19: ffff0000080521e7 x18: 000000000000000d
  x17: 00000000000038ff x16: 0000000000000002
  x15: 0000000000000007 x14: 0000000000007fff
  x13: ffffff0000000000 x12: 0000000000000018
  x11: 000000001fffd200 x10: 00000000ffffff76
  x9 : 000000000000005f x8 : ffff000008725fa8
  x7 : ffff000008a8df70 x6 : ffff000008a8df70
  x5 : ffff000008a8d000 x4 : 0000000000000010
  x3 : 0000000000000010 x2 : 000000000000000c
  x1 : 0000000000000006 x0 : 0000000000000000
  ...
    acpi_ns_lookup+0x520/0x734
    acpi_ds_load1_begin_op+0x174/0x4fc
    acpi_ps_build_named_op+0xf8/0x220
    acpi_ps_create_op+0x208/0x33c
    acpi_ps_parse_loop+0x204/0x838
    acpi_ps_parse_aml+0x1bc/0x42c
    acpi_ns_one_complete_parse+0x1e8/0x22c
    acpi_ns_parse_table+0x8c/0x128
    acpi_ns_load_table+0xc0/0x1e8
    acpi_tb_load_namespace+0xf8/0x2e8
    acpi_load_tables+0x7c/0x110
    acpi_init+0x90/0x2c0
    do_one_initcall+0x38/0x12c
    kernel_init_freeable+0x148/0x1ec
    kernel_init+0x10/0xec
    ret_from_fork+0x10/0x40
  Code: b9009fbc 2a00037b 36380057 3219037b (b9400260)
  ---[ end trace 03381e5eb0a24de4 ]---
  Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

With 'efi=debug', we can see those ACPI regions loaded by firmware on
that board as:

  efi:   0x0083ff185000-0x0083ff1b4fff [Reserved           |   |  |  |  |  |  |  |   |WB|WT|WC|UC]*
  efi:   0x0083ff1b5000-0x0083ff1c2fff [ACPI Reclaim Memory|   |  |  |  |  |  |  |   |WB|WT|WC|UC]*
  efi:   0x0083ff223000-0x0083ff224fff [ACPI Memory NVS    |   |  |  |  |  |  |  |   |WB|WT|WC|UC]*

Link: http://lkml.kernel.org/r/1468475036-5852-3-git-send-email-dennis.chen@arm.com


Acked-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Dennis Chen <dennis.chen@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Kaly Xin <kaly.xin@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>