On Fri, Dec 15, 2017 at 3:05 PM, Ard Biesheuvel
<ard.biesheuvel(a)linaro.org> wrote:
On 15 December 2017 at 09:59, AKASHI Takahiro
<takahiro.akashi(a)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(a)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(a)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/ke...
>> >> >> , 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=".
>>