Re: arm64 crashkernel fails to boot on acpi-only machines due to ACPI regions being no longer mapped as NOMAP

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Sun, Dec 24, 2017 at 01:21:02AM +0530, Bhupesh Sharma wrote:
> On Fri, Dec 22, 2017 at 2:03 PM, AKASHI Takahiro
> <takahiro.akashi@linaro.org> wrote:
> > On Thu, Dec 21, 2017 at 05:36:30PM +0530, Bhupesh Sharma wrote:
> >> Hello Akashi,
> >>
> >> On Thu, Dec 21, 2017 at 4:04 PM, AKASHI Takahiro
> >> <takahiro.akashi@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@linaro.org> wrote:
> >> >> > On 19 December 2017 at 07:09, AKASHI Takahiro
> >> >> > <takahiro.akashi@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@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@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, &reg);
> >> >> >>> > > >> >>
> >> >> >>> > > >> >>         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@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, &reg);
> >> >
> >> > -       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
> >
> > These messages shows that some "struct page" data are allocated on remote
> > (numa) nodes.
> > Since on your crash dump kernel, all the usable system memory (starting
> > 0x0e800000) belongs to Node#0, we can't avoid such non-local allocations.
> >
> > In my best guess, you can ingore them except for some performance penality.
> > This may be one side-effect.
> >
> > So does your crash dump kernel now boot successfully?
> >
> 
> Indeed. The crash dump kernel now boots successfully and the crash
> dump core can be saved properly as well (I tried saving it to local
> disk).

Thank you for the confirmation.
(I'd like to suggest you to examine the core dump with crash utility.)

> However, the 'potential offnode page_structs' WARN messages hog the
> console and delay crashkernel boot for a significant duration, which
> can be irritating.
> 
> Can we also consider ratelimiting this WARNING message [which seems to
> come from vmemmap_verify()] if invoked in the context of crash kernel,
> in addition to making the above change suggested by  you.

Well, we may be able to change pr_warn() to pr_warn_once() here, but
I hope that adding "numa=off" to kernel command line should also work.

Thanks,
-Takahiro AKASHI


> Thanks for the help.
> 
> Regards,
> Bhupesh

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