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

[Ard Biesheuvel]

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, &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 ...]


>> 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?

>
>>
>> >> 6b). The kernel code currently looks like the following:
>> >>
>> >> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> >> index 30ad2f085d1f..867bdec7c692 100644
>> >> --- a/arch/arm64/kernel/setup.c
>> >> +++ b/arch/arm64/kernel/setup.c
>> >> @@ -206,6 +206,7 @@ static void __init request_standard_resources(void)
>> >>  {
>> >>      struct memblock_region *region;
>> >>      struct resource *res;
>> >> +    phys_addr_t addr_start, addr_end;
>> >>
>> >>      kernel_code.start   = __pa_symbol(_text);
>> >>      kernel_code.end     = __pa_symbol(__init_begin - 1);
>> >> @@ -218,9 +219,17 @@ static void __init request_standard_resources(void)
>> >>              res->name  = "reserved";
>> >>              res->flags = IORESOURCE_MEM;
>> >>          } else {
>> >> -            res->name  = "System RAM";
>> >> -            res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>> >> +            addr_start =
>> >> __pfn_to_phys(memblock_region_reserved_base_pfn(region));
>> >> +            addr_end =
>> >> __pfn_to_phys(memblock_region_reserved_end_pfn(region)) - 1;
>> >> +            if ((efi_mem_type(addr_start) == EFI_ACPI_RECLAIM_MEMORY)
>> >> || (efi_mem_type(addr_end) == EFI_ACPI_RECLAIM_MEMORY)) {
>> >> +                res->name  = "ACPI reclaim region";
>> >> +                res->flags = IORESOURCE_MEM;
>> >> +            } else {
>> >> +                res->name  = "System RAM";
>> >> +                res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>> >> +            }
>> >>          }
>> >> +
>> >>          res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
>> >>          res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1;
>> >>
>> >> @@ -292,6 +301,7 @@ void __init setup_arch(char **cmdline_p)
>> >>
>> >>      request_standard_resources();
>> >>
>> >> +    efi_memmap_unmap();
>> >>      early_ioremap_reset();
>> >>
>> >>      if (acpi_disabled)
>> >> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
>> >> index 80d1a885def5..a7c522eac640 100644
>> >> --- a/drivers/firmware/efi/arm-init.c
>> >> +++ b/drivers/firmware/efi/arm-init.c
>> >> @@ -259,7 +259,6 @@ void __init efi_init(void)
>> >>
>> >>      reserve_regions();
>> >>      efi_esrt_init();
>> >> -    efi_memmap_unmap();
>> >>
>> >>      memblock_reserve(params.mmap & PAGE_MASK,
>> >>               PAGE_ALIGN(params.mmap_size +
>> >>
>> >>
>> >> After this change the ACPI reclaim regions are properly recognized in
>> >> '/proc/iomem':
>> >>
>> >> # cat /proc/iomem | grep -i ACPI
>> >> 396c0000-3975ffff : ACPI reclaim region
>> >> 39770000-397affff : ACPI reclaim region
>> >> 398a0000-398bffff : ACPI reclaim region
>> >>
>> >> 6c). I am currently changing the 'kexec-tools' and will finish the
>> >> testing over the next few days.
>> >>
>> >> I just wanted to know your opinion on this issue, so that I will be
>> >> able to propose a fix on the above lines.
>> >>
>> >> Also Cc'ing kexec mailing list for more inputs on changes proposed to
>> >> kexec-tools.
>> >>
>> >> Thanks,
>> >> Bhupesh