Re: [PATCH] arm64: kdump: retain reserved memory regions

From: James Morse <james.morse@arm.com>
To: AKASHI Takahiro <takahiro.akashi@linaro.org>,
	catalin.marinas@arm.com, will.deacon@arm.com
Cc: dyoung@redhat.com, bhsharma@redhat.com,
	kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org,
	ard.biesheuvel@linaro.org
Subject: Re: [PATCH] arm64: kdump: retain reserved memory regions
Date: Wed, 10 Jan 2018 11:26:55 +0000	[thread overview]
Message-ID: <5A55F87F.2080501@arm.com> (raw)
In-Reply-To: <20180110100943.6082-1-takahiro.akashi@linaro.org>

Hi Akashi,

On 10/01/18 10:09, 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."
> 
> 	<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.

Ugh, because acpi_os_ioremap() looks at the efi memory map through the prism of
what we pulled into memblock, which is different during kdump.

Is an alternative to teach acpi_os_ioremap() to ask
efi_mem_attributes() directly for the attributes to use?
(e.g. arch_apei_get_mem_attribute())

> * 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.

Thanks,

James

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec