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>]

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


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