arm64 crashkernel fails to boot on acpi-only machines due to ACPI regions being no longer mapped as NOMAP
Bhupesh Sharma
bhsharma at redhat.com
Sun Dec 17 13:01:27 PST 2017
On Fri, Dec 15, 2017 at 3:05 PM, Ard Biesheuvel
<ard.biesheuvel at linaro.org> wrote:
> On 15 December 2017 at 09:59, AKASHI Takahiro
> <takahiro.akashi at linaro.org> wrote:
>> On Wed, Dec 13, 2017 at 12:17:22PM +0000, Ard Biesheuvel wrote:
>>> On 13 December 2017 at 12:16, AKASHI Takahiro
>>> <takahiro.akashi at linaro.org> wrote:
>>> > On Wed, Dec 13, 2017 at 10:49:27AM +0000, Ard Biesheuvel wrote:
>>> >> On 13 December 2017 at 10:26, AKASHI Takahiro
>>> >> <takahiro.akashi at linaro.org> wrote:
>>> >> > Bhupesh, Ard,
>>> >> >
>>> >> > On Wed, Dec 13, 2017 at 03:21:59AM +0530, Bhupesh Sharma wrote:
>>> >> >> Hi Ard, Akashi
>>> >> >>
>>> >> > (snip)
>>> >> >
>>> >> >> Looking deeper into the issue, since the arm64 kexec-tools uses the
>>> >> >> 'linux,usable-memory-range' dt property to allow crash dump kernel to
>>> >> >> identify its own usable memory and exclude, at its boot time, any
>>> >> >> other memory areas that are part of the panicked kernel's memory.
>>> >> >> (see https://www.kernel.org/doc/Documentation/devicetree/bindings/chosen.txt
>>> >> >> , for details)
>>> >> >
>>> >> > Right.
>>> >> >
>>> >> >> 1). Now when 'kexec -p' is executed, this node is patched up only
>>> >> >> with the crashkernel memory range:
>>> >> >>
>>> >> >> /* add linux,usable-memory-range */
>>> >> >> nodeoffset = fdt_path_offset(new_buf, "/chosen");
>>> >> >> result = fdt_setprop_range(new_buf, nodeoffset,
>>> >> >> PROP_USABLE_MEM_RANGE, &crash_reserved_mem,
>>> >> >> address_cells, size_cells);
>>> >> >>
>>> >> >> (see https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git/tree/kexec/arch/arm64/kexec-arm64.c#n465
>>> >> >> , for details)
>>> >> >>
>>> >> >> 2). This excludes the ACPI reclaim regions irrespective of whether
>>> >> >> they are marked as System RAM or as RESERVED. As,
>>> >> >> 'linux,usable-memory-range' dt node is patched up only with
>>> >> >> 'crash_reserved_mem' and not 'system_memory_ranges'
>>> >> >>
>>> >> >> 3). As a result when the crashkernel boots up it doesn't find this
>>> >> >> ACPI memory and crashes while trying to access the same:
>>> >> >>
>>> >> >> # kexec -p /boot/vmlinuz-`uname -r` --initrd=/boot/initramfs-`uname
>>> >> >> -r`.img --reuse-cmdline -d
>>> >> >>
>>> >> >> [snip..]
>>> >> >>
>>> >> >> Reserved memory range
>>> >> >> 000000000e800000-000000002e7fffff (0)
>>> >> >>
>>> >> >> Coredump memory ranges
>>> >> >> 0000000000000000-000000000e7fffff (0)
>>> >> >> 000000002e800000-000000003961ffff (0)
>>> >> >> 0000000039d40000-000000003ed2ffff (0)
>>> >> >> 000000003ed60000-000000003fbfffff (0)
>>> >> >> 0000001040000000-0000001ffbffffff (0)
>>> >> >> 0000002000000000-0000002ffbffffff (0)
>>> >> >> 0000009000000000-0000009ffbffffff (0)
>>> >> >> 000000a000000000-000000affbffffff (0)
>>> >> >>
>>> >> >> 4). So if we revert Ard's patch or just comment the fixing up of the
>>> >> >> memory cap'ing passed to the crash kernel inside
>>> >> >> 'arch/arm64/mm/init.c' (see below):
>>> >> >>
>>> >> >> static void __init fdt_enforce_memory_region(void)
>>> >> >> {
>>> >> >> struct memblock_region reg = {
>>> >> >> .size = 0,
>>> >> >> };
>>> >> >>
>>> >> >> of_scan_flat_dt(early_init_dt_scan_usablemem, ®);
>>> >> >>
>>> >> >> if (reg.size)
>>> >> >> //memblock_cap_memory_range(reg.base, reg.size); /*
>>> >> >> comment this out */
>>> >> >> }
>>> >> >
>>> >> > Please just don't do that. It can cause a fatal damage on
>>> >> > memory contents of the *crashed* kernel.
>>> >> >
>>> >> >> 5). Both the above temporary solutions fix the problem.
>>> >> >>
>>> >> >> 6). However exposing all System RAM regions to the crashkernel is not
>>> >> >> advisable and may cause the crashkernel or some crashkernel drivers to
>>> >> >> fail.
>>> >> >>
>>> >> >> 6a). I am trying an approach now, where the ACPI reclaim regions are
>>> >> >> added to '/proc/iomem' separately as ACPI reclaim regions by the
>>> >> >> kernel code and on the other hand the user-space 'kexec-tools' will
>>> >> >> pick up the ACPI reclaim regions from '/proc/iomem' and add it to the
>>> >> >> dt node 'linux,usable-memory-range'
>>> >> >
>>> >> > I still don't understand why we need to carry over the information
>>> >> > about "ACPI Reclaim memory" to crash dump kernel. In my understandings,
>>> >> > such regions are free to be reused by the kernel after some point of
>>> >> > initialization. Why does crash dump kernel need to know about them?
>>> >> >
>>> >>
>>> >> Not really. According to the UEFI spec, they can be reclaimed after
>>> >> the OS has initialized, i.e., when it has consumed the ACPI tables and
>>> >> no longer needs them. Of course, in order to be able to boot a kexec
>>> >> kernel, those regions needs to be preserved, which is why they are
>>> >> memblock_reserve()'d now.
>>> >
>>> > For my better understandings, who is actually accessing such regions
>>> > during boot time, uefi itself or efistub?
>>> >
>>>
>>> No, only the kernel. This is where the ACPI tables are stored. For
>>> instance, on QEMU we have
>>>
>>> ACPI: RSDP 0x0000000078980000 000024 (v02 BOCHS )
>>> ACPI: XSDT 0x0000000078970000 000054 (v01 BOCHS BXPCFACP 00000001
>>> 01000013)
>>> ACPI: FACP 0x0000000078930000 00010C (v05 BOCHS BXPCFACP 00000001
>>> BXPC 00000001)
>>> ACPI: DSDT 0x0000000078940000 0011DA (v02 BOCHS BXPCDSDT 00000001
>>> BXPC 00000001)
>>> ACPI: APIC 0x0000000078920000 000140 (v03 BOCHS BXPCAPIC 00000001
>>> BXPC 00000001)
>>> ACPI: GTDT 0x0000000078910000 000060 (v02 BOCHS BXPCGTDT 00000001
>>> BXPC 00000001)
>>> ACPI: MCFG 0x0000000078900000 00003C (v01 BOCHS BXPCMCFG 00000001
>>> BXPC 00000001)
>>> ACPI: SPCR 0x00000000788F0000 000050 (v02 BOCHS BXPCSPCR 00000001
>>> BXPC 00000001)
>>> ACPI: IORT 0x00000000788E0000 00007C (v00 BOCHS BXPCIORT 00000001
>>> BXPC 00000001)
>>>
>>> covered by
>>>
>>> efi: 0x0000788e0000-0x00007894ffff [ACPI Reclaim Memory ...]
>>> ...
>>> efi: 0x000078970000-0x00007898ffff [ACPI Reclaim Memory ...]
>>
>> OK. I mistakenly understood those regions could be freed after exiting
>> UEFI boot services.
>>
>>>
>>> >> So it seems that kexec does not honour the memblock_reserve() table
>>> >> when booting the next kernel.
>>> >
>>> > not really.
>>> >
>>> >> > (In other words, can or should we skip some part of ACPI-related init code
>>> >> > on crash dump kernel?)
>>> >> >
>>> >>
>>> >> I don't think so. And the change to the handling of ACPI reclaim
>>> >> regions only revealed the bug, not created it (given that other
>>> >> memblock_reserve regions may be affected as well)
>>> >
>>> > As whether we should honor such reserved regions over kexec'ing
>>> > depends on each one's specific nature, we will have to take care one-by-one.
>>> > As a matter of fact, no information about "reserved" memblocks is
>>> > exposed to user space (via proc/iomem).
>>> >
>>>
>>> That is why I suggested (somewhere in this thread?) to not expose them
>>> as 'System RAM'. Do you think that could solve this?
>>
>> Memblock-reserv'ing them is necessary to prevent their corruption and
>> marking them under another name in /proc/iomem would also be good in order
>> not to allocate them as part of crash kernel's memory.
>>
>
> I agree. However, this may not be entirely trivial, since iterating
> over the memblock_reserved table and creating iomem entries may result
> in collisions.
I found a method (using the patch I shared earlier in this thread) to mark these
entries as 'ACPI reclaim memory' ranges rather than System RAM or
reserved regions.
>> But I'm not still convinced that we should export them in useable-
>> memory-range to crash dump kernel. They will be accessed through
>> acpi_os_map_memory() and so won't be required to be part of system ram
>> (or memblocks), I guess.
>
> Agreed. They will be covered by the linear mapping in the boot kernel,
> and be mapped explicitly via ioremap_cache() in the kexec kernel,
> which is exactly what we want in this case.
Now this is what is confusing me. I don't see the above happening.
I see that the primary kernel boots up and adds the ACPI regions via:
acpi_os_ioremap
-> ioremap_cache
But during the crashkernel boot, ''acpi_os_ioremap' calls
'ioremap' for the ACPI Reclaim Memory regions and not the _cache
variant.
And it fails while accessing the ACPI tables:
[ 0.039205] ACPI: Core revision 20170728
pud=000000002e7d0003, *pmd=000000002e7c0003, *pte=00e8000039710707
[ 0.095098] Internal error: Oops: 96000021 [#1] SMP
[ 0.100022] Modules linked in:
[ 0.103102] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc6 #1
[ 0.109432] task: ffff000008d05180 task.stack: ffff000008cc0000
[ 0.115414] PC is at acpi_ns_lookup+0x25c/0x3c0
[ 0.119987] LR is at acpi_ds_load1_begin_op+0xa4/0x294
[ 0.125175] pc : [<ffff0000084a6764>] lr : [<ffff00000849b4f8>]
pstate: 60000045
[ 0.132647] sp : ffff000008ccfb40
[ 0.135989] x29: ffff000008ccfb40 x28: ffff000008a9f2a4
[ 0.141354] x27: ffff0000088be820 x26: 0000000000000000
[ 0.146718] x25: 000000000000001b x24: 0000000000000001
[ 0.152083] x23: 0000000000000001 x22: ffff000009710027
[ 0.157447] x21: ffff000008ccfc50 x20: 0000000000000001
[ 0.162812] x19: 000000000000001b x18: 0000000000000005
[ 0.168176] x17: 0000000000000000 x16: 0000000000000000
[ 0.173541] x15: 0000000000000000 x14: 000000000000038e
[ 0.178905] x13: ffffffff00000000 x12: ffffffffffffffff
[ 0.184270] x11: 0000000000000006 x10: 00000000ffffff76
[ 0.189634] x9 : 000000000000005f x8 : ffff8000126d0140
[ 0.194998] x7 : 0000000000000000 x6 : ffff000008ccfc50
[ 0.200362] x5 : ffff80000fe62c00 x4 : 0000000000000001
[ 0.205727] x3 : ffff000008ccfbe0 x2 : ffff0000095e3980
[ 0.211091] x1 : ffff000009710027 x0 : 0000000000000000
[ 0.216456] Process swapper/0 (pid: 0, stack limit = 0xffff000008cc0000)
[ 0.223224] Call trace:
[ 0.225688] Exception stack(0xffff000008ccfa00 to 0xffff000008ccfb40)
[ 0.232194] fa00: 0000000000000000 ffff000009710027
ffff0000095e3980 ffff000008ccfbe0
[ 0.240106] fa20: 0000000000000001 ffff80000fe62c00
ffff000008ccfc50 0000000000000000
[ 0.248018] fa40: ffff8000126d0140 000000000000005f
00000000ffffff76 0000000000000006
[ 0.255931] fa60: ffffffffffffffff ffffffff00000000
000000000000038e 0000000000000000
[ 0.263843] fa80: 0000000000000000 0000000000000000
0000000000000005 000000000000001b
[ 0.271754] faa0: 0000000000000001 ffff000008ccfc50
ffff000009710027 0000000000000001
[ 0.279667] fac0: 0000000000000001 000000000000001b
0000000000000000 ffff0000088be820
[ 0.287579] fae0: ffff000008a9f2a4 ffff000008ccfb40
ffff00000849b4f8 ffff000008ccfb40
[ 0.295491] fb00: ffff0000084a6764 0000000060000045
ffff000008ccfb40 ffff000008260a18
[ 0.303403] fb20: ffffffffffffffff ffff0000087f3fb0
ffff000008ccfb40 ffff0000084a6764
[ 0.311316] [<ffff0000084a6764>] acpi_ns_lookup+0x25c/0x3c0
[ 0.316943] [<ffff00000849b4f8>] acpi_ds_load1_begin_op+0xa4/0x294
[ 0.323186] [<ffff0000084ad4ac>] acpi_ps_build_named_op+0xc4/0x198
[ 0.329428] [<ffff0000084ad6cc>] acpi_ps_create_op+0x14c/0x270
[ 0.335319] [<ffff0000084acfa8>] acpi_ps_parse_loop+0x188/0x5c8
[ 0.341298] [<ffff0000084ae048>] acpi_ps_parse_aml+0xb0/0x2b8
[ 0.347101] [<ffff0000084a8e10>] acpi_ns_one_complete_parse+0x144/0x184
[ 0.353783] [<ffff0000084a8e98>] acpi_ns_parse_table+0x48/0x68
[ 0.359675] [<ffff0000084a82cc>] acpi_ns_load_table+0x4c/0xdc
[ 0.365479] [<ffff0000084b32f8>] acpi_tb_load_namespace+0xe4/0x264
[ 0.371723] [<ffff000008baf9b4>] acpi_load_tables+0x48/0xc0
[ 0.377350] [<ffff000008badc20>] acpi_early_init+0x9c/0xd0
[ 0.382891] [<ffff000008b70d50>] start_kernel+0x3b4/0x43c
[ 0.388343] Code: b9008fb9 2a000318 36380054 32190318 (b94002c0)
[ 0.394500] ---[ end trace c46ed37f9651c58e ]---
[ 0.399160] Kernel panic - not syncing: Fatal exception
[ 0.404437] Rebooting in 10 seconds.
So, I think the linear mapping done by the primary kernel does not
make these accessible in the crash kernel directly.
Any pointers?
Regards,
Bhupesh
>> Just FYI, on x86, ACPI tables seems to be exposed to crash dump kernel
>> via a kernel command line parameter, "memmap=".
>>
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