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
Thu Dec 21 04:06:30 PST 2017
Hello Akashi,
On Thu, Dec 21, 2017 at 4:04 PM, AKASHI Takahiro
<takahiro.akashi at linaro.org> wrote:
> Bhupesh,
>
> Can you test the patch attached below, please?
>
> It is intended to retain already-reserved regions (ACPI reclaim memory
> in this case) in system ram (i.e. memblock.memory) without explicitly
> exporting them via usable-memory-range.
> (I still have to figure out what the side-effect of this patch is.)
>
> Thanks,
> -Takahiro AKASHI
>
> On Thu, Dec 21, 2017 at 01:30:43AM +0530, Bhupesh Sharma wrote:
>> On Tue, Dec 19, 2017 at 6:39 PM, Ard Biesheuvel
>> <ard.biesheuvel at linaro.org> wrote:
>> > On 19 December 2017 at 07:09, AKASHI Takahiro
>> > <takahiro.akashi at linaro.org> wrote:
>> >> On Mon, Dec 18, 2017 at 01:40:09PM +0800, Dave Young wrote:
>> >>> On 12/15/17 at 05:59pm, AKASHI Takahiro 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.
>> >>> >
>> >>> > 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.
>> >>> > -> Bhupesh?
>> >>>
>> >>> I forgot how arm64 kernel retrieve the memory ranges and initialize
>> >>> them. If no "e820" like interfaces shouldn't kernel reinitialize all
>> >>> the memory according to the efi memmap? For kdump kernel anything other
>> >>> than usable memory (which is from the dt node instead) should be
>> >>> reinitialized according to efi passed info, no?
>> >>
>> >> All the regions exported in efi memmap will be added to memblock.memory
>> >> in (u)efi_init() and then trimmed down to the exact range specified as
>> >> usable-memory-range by fdt_enforce_memory_region().
>> >>
>> >> Now I noticed that the current fdt_enforce_memory_region() may not work well
>> >> with multiple entries in usable-memory-range.
>> >>
>> >
>> > In any case, the root of the problem is that memory regions lose their
>> > 'memory' annotation due to the way the memory map is mangled before
>> > being supplied to the kexec kernel.
>> >
>> > Would it be possible to classify all memory that we want to hide from
>> > the kexec kernel as NOMAP instead? That way, it will not be mapped
>> > implicitly, but will still be mapped cacheable by acpi_os_ioremap(),
>> > so this seems to be the most appropriate way to deal with the host
>> > kernel's memory contents.
>>
>> Hmm. wouldn't appending the acpi reclaim regions to
>> 'linux,usable-memory-range' in the dtb being passed to the crashkernel
>> be better? Because its indirectly achieving a similar objective
>> (although may be a subset of all System RAM regions on the primary
>> kernel's memory).
>>
>> I am not aware of the background about the current kexec-tools
>> implementation where we add only the crashkernel range to the dtb
>> being passed to the crashkernel.
>>
>> Probably Akashi can answer better, as to how we arrived at this design
>> approach and why we didn't want to expose all System RAM regions (i.e.
>> ! NOMPAP regions) to the crashkernel.
>>
>> I am suspecting that some issues were seen/meet when the System RAM (!
>> NOMAP regions) were exposed to the crashkernel, and that's why we
>> finalized on this design approach, but this is something which is just
>> my guess.
>>
>> Regards,
>> Bhupesh
>>
>> >>> >
>> >>> > Just FYI, on x86, ACPI tables seems to be exposed to crash dump kernel
>> >>> > via a kernel command line parameter, "memmap=".
>> >>>
>> >>> memmap= is only used in old kexec-tools, now we are passing them via
>> >>> e820 table.
>> >>
>> >> Thanks. I remember that you have explained it before.
>> >>
>> >> -Takahiro AKASHI
>> >>
>> >>> [snip]
>> >>>
>> >>> Thanks
>> >>> Dave
>
> ===8<==
> From 74e2451fea83d546feae76160ba7de426913fe03 Mon Sep 17 00:00:00 2001
> From: AKASHI Takahiro <takahiro.akashi at linaro.org>
> Date: Thu, 21 Dec 2017 19:14:23 +0900
> Subject: [PATCH] arm64: kdump: mark unusable memory as NOMAP
>
> ---
> arch/arm64/mm/init.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 00e7b900ca41..8175db94257b 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -352,11 +352,17 @@ 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, ®);
>
> - if (reg.size)
> - memblock_cap_memory_range(reg.base, reg.size);
> + if (reg.size) {
> + for_each_free_mem_range(idx, NUMA_NO_NODE, MEMBLOCK_NONE,
> + &start, &end, NULL)
> + memblock_mark_nomap(start, end - start);
> + memblock_clear_nomap(reg.base, reg.size);
> + }
> }
>
> void __init arm64_memblock_init(void)
> --
> 2.15.1
>
Thanks for the patch. After applying this on top of
4.15.0-rc4-next-20171220, there seems to be a improvement and the
crashkernel boot no longer hangs while trying to access the acpi
tables.
However I notice a minor issue. Please see the log below for
reference, the following message keeps spamming the console but I see
the crashkernel boot proceed further.:
[ 0.000000] ACPI: NUMA: SRAT: PXM 3 -> MPIDR 0x70303 -> Node 3
[ 0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x3fffffff]
[ 0.000000] ACPI: SRAT: Node 1 PXM 1 [mem 0x2000000000-0x2fffffffff]
[ 0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x1000000000-0x1fffffffff]
[ 0.000000] ACPI: SRAT: Node 3 PXM 3 [mem 0xa000000000-0xafffffffff]
[ 0.000000] ACPI: SRAT: Node 2 PXM 2 [mem 0x9000000000-0x9fffffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x1ffbffe200-0x1ffbffffff]
[ 0.000000] NUMA: NODE_DATA [mem 0x1ffbffc400-0x1ffbffe1ff]
[ 0.000000] NUMA: NODE_DATA(1) on node 0
[ 0.000000] NUMA: NODE_DATA [mem 0x1ffbffa600-0x1ffbffc3ff]
[ 0.000000] NUMA: NODE_DATA(2) on node 0
[ 0.000000] NUMA: NODE_DATA [mem 0x1ffbff8800-0x1ffbffa5ff]
[ 0.000000] NUMA: NODE_DATA(3) on node 0
[ 0.000000] [ffff7fe008000000-ffff7fe00800ffff] potential offnode
page_structs
[ 0.000000] [ffff7fe008010000-ffff7fe00801ffff] potential offnode
page_structs
[ 0.000000] [ffff7fe008020000-ffff7fe00802ffff] potential offnode
page_structs
[ 0.000000] [ffff7fe008030000-ffff7fe00803ffff] potential offnode
page_structs
[ 0.000000] [ffff7fe008040000-ffff7fe00804ffff] potential offnode
page_structs
[ 0.000000] [ffff7fe008050000-ffff7fe00805ffff] potential offnode
page_structs
[snip..]
[ 0.000000] [ffff7fe0081f0000-ffff7fe0081fffff] potential offnode
page_structs
This WARNING message seems to come from vmemmap_verify() inside
'mm/sparse-vmemmap.c'
Regards,
Bhupesh
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