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

[takahiro.akashi@linaro.org (AKASHI Takahiro)]

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?

Just FYI, on x86, ACPI tables seems to be exposed to crash dump kernel
via a kernel command line parameter, "memmap=".

Thanks,
-Takahiro AKASHI


> >
> >>
> >> >> 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