[PATCH v6 2/2] arm64:acpi Fix the acpi alignment exception when 'mem=' specified

[Dennis Chen]

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 un-aligned
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':
...
[    0.542475] Unable to handle kernel paging request at virtual address ffff0000080521e7
[    0.550457] pgd = ffff000008aa0000
[    0.553880] [ffff0000080521e7] *pgd=000000801fffe003, *pud=000000801fffd003, *pmd=000000801fffc003, *pte=00e80083ff1c1707
[    0.564939] Internal error: Oops: 96000021 [#1] PREEMPT SMP
[    0.570553] Modules linked in:
[    0.573626] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc3-next-20160616+ #172
[    0.581344] Hardware name: AMD Overdrive/Supercharger/Default string, BIOS ROD1001A 02/09/2016
[    0.590025] task: ffff800001ef0000 ti: ffff800001ef8000 task.ti: ffff800001ef8000
[    0.597571] PC is at acpi_ns_lookup+0x520/0x734
[    0.602134] LR is at acpi_ns_lookup+0x4a4/0x734
[    0.606693] pc : [<ffff0000083b8b10>] lr : [<ffff0000083b8a94>] pstate: 60000045
[    0.614145] sp : ffff800001efb8b0
[    0.617478] x29: ffff800001efb8c0 x28: 000000000000001b
[    0.622829] x27: 0000000000000001 x26: 0000000000000000
[    0.628181] x25: ffff800001efb9e8 x24: ffff000008a10000
[    0.633531] x23: 0000000000000001 x22: 0000000000000001
[    0.638881] x21: ffff000008724000 x20: 000000000000001b
[    0.644230] x19: ffff0000080521e7 x18: 000000000000000d
[    0.649580] x17: 00000000000038ff x16: 0000000000000002
[    0.654929] x15: 0000000000000007 x14: 0000000000007fff
[    0.660278] x13: ffffff0000000000 x12: 0000000000000018
[    0.665627] x11: 000000001fffd200 x10: 00000000ffffff76
[    0.670978] x9 : 000000000000005f x8 : ffff000008725fa8
[    0.676328] x7 : ffff000008a8df70 x6 : ffff000008a8df70
[    0.681679] x5 : ffff000008a8d000 x4 : 0000000000000010
[    0.687027] x3 : 0000000000000010 x2 : 000000000000000c
[    0.692378] x1 : 0000000000000006 x0 : 0000000000000000
...
[    1.262235] [<ffff0000083b8b10>] acpi_ns_lookup+0x520/0x734
[    1.267845] [<ffff0000083a7160>] acpi_ds_load1_begin_op+0x174/0x4fc
[    1.274156] [<ffff0000083c1f4c>] acpi_ps_build_named_op+0xf8/0x220
[    1.280380] [<ffff0000083c227c>] acpi_ps_create_op+0x208/0x33c
[    1.286254] [<ffff0000083c1820>] acpi_ps_parse_loop+0x204/0x838
[    1.292215] [<ffff0000083c2fd4>] acpi_ps_parse_aml+0x1bc/0x42c
[    1.298090] [<ffff0000083bc6e8>] acpi_ns_one_complete_parse+0x1e8/0x22c
[    1.304753] [<ffff0000083bc7b8>] acpi_ns_parse_table+0x8c/0x128
[    1.310716] [<ffff0000083bb8fc>] acpi_ns_load_table+0xc0/0x1e8
[    1.316591] [<ffff0000083c9068>] acpi_tb_load_namespace+0xf8/0x2e8
[    1.322818] [<ffff000008984128>] acpi_load_tables+0x7c/0x110
[    1.328516] [<ffff000008982ea4>] acpi_init+0x90/0x2c0
[    1.333603] [<ffff0000080819fc>] do_one_initcall+0x38/0x12c
[    1.339215] [<ffff000008960cd4>] kernel_init_freeable+0x148/0x1ec
[    1.345353] [<ffff0000086b7d30>] kernel_init+0x10/0xec
[    1.350529] [<ffff000008084e10>] ret_from_fork+0x10/0x40
[    1.355878] Code: b9009fbc 2a00037b 36380057 3219037b (b9400260)
[    1.362035] ---[ end trace 03381e5eb0a24de4 ]---
[    1.366691] 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:
[    0.000000] efi:   0x0083ff185000-0x0083ff1b4fff [Reserved           |   |  |  |  |  |  |  |   |WB|WT|WC|UC]*
[    0.000000] efi:   0x0083ff1b5000-0x0083ff1c2fff [ACPI Reclaim Memory|   |  |  |  |  |  |  |   |WB|WT|WC|UC]*
[    0.000000] efi:   0x0083ff223000-0x0083ff224fff [ACPI Memory NVS    |   |  |  |  |  |  |  |   |WB|WT|WC|UC]*

Acked-by: Steve Capper <steve.capper at arm.com>
Signed-off-by: Dennis Chen <dennis.chen at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Pekka Enberg <penberg at kernel.org>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Tang Chen <tangchen at cn.fujitsu.com>
Cc: Tony Luck <tony.luck at intel.com>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Rafael J. Wysocki <rafael at kernel.org>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Matt Fleming <matt at codeblueprint.co.uk>
Cc: Kaly Xin <kaly.xin at arm.com>
Cc: linux-mm at kvack.org
Cc: linux-acpi at vger.kernel.org
Cc: linux-efi at vger.kernel.org
---
 arch/arm64/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 7d25b4d..9482b45 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -226,7 +226,7 @@ void __init arm64_memblock_init(void)
 	 * via the linear mapping.
 	 */
 	if (memory_limit != (phys_addr_t)ULLONG_MAX) {
-		memblock_enforce_memory_limit(memory_limit);
+		memblock_mem_limit_remove_map(memory_limit);
 		memblock_add(__pa(_text), (u64)(_end - _text));
 	}
 
-- 
2.7.4