On Fri, Dec 15, 2017 at 3:05 PM, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > On 15 December 2017 at 09:59, AKASHI Takahiro > <takahiro.akashi@xxxxxxxxxx> 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, ®); >>> >> >> >>> >> >> 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. >> > > I agree. However, this may not be entirely trivial, since iterating > over the memblock_reserved table and creating iomem entries may result > in collisions. I found a method (using the patch I shared earlier in this thread) to mark these entries as 'ACPI reclaim memory' ranges rather than System RAM or reserved regions. >> 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. > > Agreed. They will be covered by the linear mapping in the boot kernel, > and be mapped explicitly via ioremap_cache() in the kexec kernel, > which is exactly what we want in this case. Now this is what is confusing me. I don't see the above happening. I see that the primary kernel boots up and adds the ACPI regions via: acpi_os_ioremap -> ioremap_cache But during the crashkernel boot, ''acpi_os_ioremap' calls 'ioremap' for the ACPI Reclaim Memory regions and not the _cache variant. And it fails while accessing the ACPI tables: [ 0.039205] ACPI: Core revision 20170728 pud=000000002e7d0003, *pmd=000000002e7c0003, *pte=00e8000039710707 [ 0.095098] Internal error: Oops: 96000021 [#1] SMP [ 0.100022] Modules linked in: [ 0.103102] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc6 #1 [ 0.109432] task: ffff000008d05180 task.stack: ffff000008cc0000 [ 0.115414] PC is at acpi_ns_lookup+0x25c/0x3c0 [ 0.119987] LR is at acpi_ds_load1_begin_op+0xa4/0x294 [ 0.125175] pc : [<ffff0000084a6764>] lr : [<ffff00000849b4f8>] pstate: 60000045 [ 0.132647] sp : ffff000008ccfb40 [ 0.135989] x29: ffff000008ccfb40 x28: ffff000008a9f2a4 [ 0.141354] x27: ffff0000088be820 x26: 0000000000000000 [ 0.146718] x25: 000000000000001b x24: 0000000000000001 [ 0.152083] x23: 0000000000000001 x22: ffff000009710027 [ 0.157447] x21: ffff000008ccfc50 x20: 0000000000000001 [ 0.162812] x19: 000000000000001b x18: 0000000000000005 [ 0.168176] x17: 0000000000000000 x16: 0000000000000000 [ 0.173541] x15: 0000000000000000 x14: 000000000000038e [ 0.178905] x13: ffffffff00000000 x12: ffffffffffffffff [ 0.184270] x11: 0000000000000006 x10: 00000000ffffff76 [ 0.189634] x9 : 000000000000005f x8 : ffff8000126d0140 [ 0.194998] x7 : 0000000000000000 x6 : ffff000008ccfc50 [ 0.200362] x5 : ffff80000fe62c00 x4 : 0000000000000001 [ 0.205727] x3 : ffff000008ccfbe0 x2 : ffff0000095e3980 [ 0.211091] x1 : ffff000009710027 x0 : 0000000000000000 [ 0.216456] Process swapper/0 (pid: 0, stack limit = 0xffff000008cc0000) [ 0.223224] Call trace: [ 0.225688] Exception stack(0xffff000008ccfa00 to 0xffff000008ccfb40) [ 0.232194] fa00: 0000000000000000 ffff000009710027 ffff0000095e3980 ffff000008ccfbe0 [ 0.240106] fa20: 0000000000000001 ffff80000fe62c00 ffff000008ccfc50 0000000000000000 [ 0.248018] fa40: ffff8000126d0140 000000000000005f 00000000ffffff76 0000000000000006 [ 0.255931] fa60: ffffffffffffffff ffffffff00000000 000000000000038e 0000000000000000 [ 0.263843] fa80: 0000000000000000 0000000000000000 0000000000000005 000000000000001b [ 0.271754] faa0: 0000000000000001 ffff000008ccfc50 ffff000009710027 0000000000000001 [ 0.279667] fac0: 0000000000000001 000000000000001b 0000000000000000 ffff0000088be820 [ 0.287579] fae0: ffff000008a9f2a4 ffff000008ccfb40 ffff00000849b4f8 ffff000008ccfb40 [ 0.295491] fb00: ffff0000084a6764 0000000060000045 ffff000008ccfb40 ffff000008260a18 [ 0.303403] fb20: ffffffffffffffff ffff0000087f3fb0 ffff000008ccfb40 ffff0000084a6764 [ 0.311316] [<ffff0000084a6764>] acpi_ns_lookup+0x25c/0x3c0 [ 0.316943] [<ffff00000849b4f8>] acpi_ds_load1_begin_op+0xa4/0x294 [ 0.323186] [<ffff0000084ad4ac>] acpi_ps_build_named_op+0xc4/0x198 [ 0.329428] [<ffff0000084ad6cc>] acpi_ps_create_op+0x14c/0x270 [ 0.335319] [<ffff0000084acfa8>] acpi_ps_parse_loop+0x188/0x5c8 [ 0.341298] [<ffff0000084ae048>] acpi_ps_parse_aml+0xb0/0x2b8 [ 0.347101] [<ffff0000084a8e10>] acpi_ns_one_complete_parse+0x144/0x184 [ 0.353783] [<ffff0000084a8e98>] acpi_ns_parse_table+0x48/0x68 [ 0.359675] [<ffff0000084a82cc>] acpi_ns_load_table+0x4c/0xdc [ 0.365479] [<ffff0000084b32f8>] acpi_tb_load_namespace+0xe4/0x264 [ 0.371723] [<ffff000008baf9b4>] acpi_load_tables+0x48/0xc0 [ 0.377350] [<ffff000008badc20>] acpi_early_init+0x9c/0xd0 [ 0.382891] [<ffff000008b70d50>] start_kernel+0x3b4/0x43c [ 0.388343] Code: b9008fb9 2a000318 36380054 32190318 (b94002c0) [ 0.394500] ---[ end trace c46ed37f9651c58e ]--- [ 0.399160] Kernel panic - not syncing: Fatal exception [ 0.404437] Rebooting in 10 seconds. So, I think the linear mapping done by the primary kernel does not make these accessible in the crash kernel directly. Any pointers? Regards, Bhupesh >> Just FYI, on x86, ACPI tables seems to be exposed to crash dump kernel >> via a kernel command line parameter, "memmap=". >> -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
