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authorWei Yang <richard.weiyang@linux.alibaba.com>2020-08-06 23:23:55 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 11:33:27 -0700
commitef69bc9f689de8380688be742f9b9df615d42429 (patch)
tree98c98d027785558f030cf8464fd8eaa92650f895 /mm/sparse-vmemmap.c
parent7a309195d11cde854eb75559fbd6b48f9e518f25 (diff)
mm/sparse: never partially remove memmap for early section
For early sections, its memmap is handled specially even sub-section is enabled. The memmap could only be populated as a whole. Quoted from the comment of section_activate(): * The early init code does not consider partially populated * initial sections, it simply assumes that memory will never be * referenced. If we hot-add memory into such a section then we * do not need to populate the memmap and can simply reuse what * is already there. While current section_deactivate() breaks this rule. When hot-remove a sub-section, section_deactivate() would depopulate its memmap. The consequence is if we hot-add this subsection again, its memmap never get proper populated. We can reproduce the case by following steps: 1. Hacking qemu to allow sub-section early section : diff --git a/hw/i386/pc.c b/hw/i386/pc.c : index 51b3050d01..c6a78d83c0 100644 : --- a/hw/i386/pc.c : +++ b/hw/i386/pc.c : @@ -1010,7 +1010,7 @@ void pc_memory_init(PCMachineState *pcms, : } : : machine->device_memory->base = : - ROUND_UP(0x100000000ULL + x86ms->above_4g_mem_size, 1 * GiB); : + 0x100000000ULL + x86ms->above_4g_mem_size; : : if (pcmc->enforce_aligned_dimm) { : /* size device region assuming 1G page max alignment per slot */ 2. Bootup qemu with PSE disabled and a sub-section aligned memory size Part of the qemu command would look like this: sudo x86_64-softmmu/qemu-system-x86_64 \ --enable-kvm -cpu host,pse=off \ -m 4160M,maxmem=20G,slots=1 \ -smp sockets=2,cores=16 \ -numa node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 \ -machine pc,nvdimm \ -nographic \ -object memory-backend-ram,id=mem0,size=8G \ -device nvdimm,id=vm0,memdev=mem0,node=0,addr=0x144000000,label-size=128k 3. Re-config a pmem device with sub-section size in guest ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M Then you would see the following call trace: pmem0: detected capacity change from 0 to 16777216 BUG: unable to handle page fault for address: ffffec73c51000b4 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 81ff8067 P4D 81ff8067 PUD 81ff7067 PMD 1437cb067 PTE 0 Oops: 0002 [#1] SMP NOPTI CPU: 16 PID: 1348 Comm: ndctl Kdump: loaded Tainted: G W 5.8.0-rc2+ #24 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.4 RIP: 0010:memmap_init_zone+0x154/0x1c2 Code: 77 16 f6 40 10 02 74 10 48 03 48 08 48 89 cb 48 c1 eb 0c e9 3a ff ff ff 48 89 df 48 c1 e7 06 48f RSP: 0018:ffffbdc7011a39b0 EFLAGS: 00010282 RAX: ffffec73c5100088 RBX: 0000000000144002 RCX: 0000000000144000 RDX: 0000000000000004 RSI: 007ffe0000000000 RDI: ffffec73c5100080 RBP: 027ffe0000000000 R08: 0000000000000001 R09: ffff9f8d38f6d708 R10: ffffec73c0000000 R11: 0000000000000000 R12: 0000000000000004 R13: 0000000000000001 R14: 0000000000144200 R15: 0000000000000000 FS: 00007efe6b65d780(0000) GS:ffff9f8d3f780000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffec73c51000b4 CR3: 000000007d718000 CR4: 0000000000340ee0 Call Trace: move_pfn_range_to_zone+0x128/0x150 memremap_pages+0x4e4/0x5a0 devm_memremap_pages+0x1e/0x60 dev_dax_probe+0x69/0x160 [device_dax] really_probe+0x298/0x3c0 driver_probe_device+0xe1/0x150 ? driver_allows_async_probing+0x50/0x50 bus_for_each_drv+0x7e/0xc0 __device_attach+0xdf/0x160 bus_probe_device+0x8e/0xa0 device_add+0x3b9/0x740 __devm_create_dev_dax+0x127/0x1c0 __dax_pmem_probe+0x1f2/0x219 [dax_pmem_core] dax_pmem_probe+0xc/0x1b [dax_pmem] nvdimm_bus_probe+0x69/0x1c0 [libnvdimm] really_probe+0x147/0x3c0 driver_probe_device+0xe1/0x150 device_driver_attach+0x53/0x60 bind_store+0xd1/0x110 kernfs_fop_write+0xce/0x1b0 vfs_write+0xb6/0x1a0 ksys_write+0x5f/0xe0 do_syscall_64+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: David Hildenbrand <david@redhat.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Dan Williams <dan.j.williams@intel.com> Link: http://lkml.kernel.org/r/20200625223534.18024-1-richard.weiyang@linux.alibaba.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/sparse-vmemmap.c')
0 files changed, 0 insertions, 0 deletions