[PATCH] arm64: kdump: retain reserved memory regions

[AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>]

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@xxxxxxxxxx>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
---
 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);
+	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


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