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 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, ®); > > > >> >> > > > >> >> 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
