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

[Dave Young]

Fix the kexec list address.

On 12/18/17 at 01:40pm, 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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?
> 
> > 
> > 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.
> 
> [snip]
> 
> Thanks
> Dave