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But how vmemmap > mappings are created are architecture specific. For example, powerpc with hash > translation doesn't have vmemmap mappings in init_mm page table instead they are > bolted table entries in the hardware page table > > vmemmap_populate_compound_pages() used by vmemmap optimization code is not aware > of these architecture-specific mapping. Hence allow architecture to opt for this > feature. I selected architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP > option as also supporting this feature. I added vmemmap_can_optimize() even > though page_vmemmap_nr(pgmap) > 1 check should filter architecture not > supporting this. IMHO that brings clarity to the code where we are populating > vmemmap. > > This patch fixes the below crash on ppc64. > > BUG: Unable to handle kernel data access on write at 0xc00c000100400038 > Faulting instruction address: 0xc000000001269d90 > Oops: Kernel access of bad area, sig: 11 [#1] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries > Modules linked in: > CPU: 7 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc5-150500.34-default+ #2 5c90a668b6bbd142599890245c2fb5de19d7d28a > Hardware name: IBM,9009-42G POWER9 (raw) 0x4e0202 0xf000005 of:IBM,FW950.40 (VL950_099) hv:phyp pSeries > NIP: c000000001269d90 LR: c0000000004c57d4 CTR: 0000000000000000 > REGS: c000000003632c30 TRAP: 0300 Not tainted (6.3.0-rc5-150500.34-default+) > MSR: 8000000000009033 CR: 24842228 XER: 00000000 > CFAR: c0000000004c57d0 DAR: c00c000100400038 DSISR: 42000000 IRQMASK: 0 > .... > NIP [c000000001269d90] __init_single_page.isra.74+0x14/0x4c > LR [c0000000004c57d4] __init_zone_device_page+0x44/0xd0 > Call Trace: > [c000000003632ed0] [c000000003632f60] 0xc000000003632f60 (unreliable) > [c000000003632f10] [c0000000004c5ca0] memmap_init_zone_device+0x170/0x250 > [c000000003632fe0] [c0000000005575f8] memremap_pages+0x2c8/0x7f0 > [c0000000036330c0] [c000000000557b5c] devm_memremap_pages+0x3c/0xa0 > [c000000003633100] [c000000000d458a8] dev_dax_probe+0x108/0x3e0 > [c0000000036331a0] [c000000000d41430] dax_bus_probe+0xb0/0x140 > [c0000000036331d0] [c000000000cef27c] really_probe+0x19c/0x520 > [c000000003633260] [c000000000cef6b4] __driver_probe_device+0xb4/0x230 > [c0000000036332e0] [c000000000cef888] driver_probe_device+0x58/0x120 > [c000000003633320] [c000000000cefa6c] __device_attach_driver+0x11c/0x1e0 > [c0000000036333a0] [c000000000cebc58] bus_for_each_drv+0xa8/0x130 > [c000000003633400] [c000000000ceefcc] __device_attach+0x15c/0x250 > [c0000000036334a0] [c000000000ced458] bus_probe_device+0x108/0x110 > [c0000000036334f0] [c000000000ce92dc] device_add+0x7fc/0xa10 > [c0000000036335b0] [c000000000d447c8] devm_create_dev_dax+0x1d8/0x530 > [c000000003633640] [c000000000d46b60] __dax_pmem_probe+0x200/0x270 > [c0000000036337b0] [c000000000d46bf0] dax_pmem_probe+0x20/0x70 > [c0000000036337d0] [c000000000d2279c] nvdimm_bus_probe+0xac/0x2b0 > [c000000003633860] [c000000000cef27c] really_probe+0x19c/0x520 > [c0000000036338f0] [c000000000cef6b4] __driver_probe_device+0xb4/0x230 > [c000000003633970] [c000000000cef888] driver_probe_device+0x58/0x120 > [c0000000036339b0] [c000000000cefd08] __driver_attach+0x1d8/0x240 > [c000000003633a30] [c000000000cebb04] bus_for_each_dev+0xb4/0x130 > [c000000003633a90] [c000000000cee564] driver_attach+0x34/0x50 > [c000000003633ab0] [c000000000ced878] bus_add_driver+0x218/0x300 > [c000000003633b40] [c000000000cf1144] driver_register+0xa4/0x1b0 > [c000000003633bb0] [c000000000d21a0c] __nd_driver_register+0x5c/0x100 > [c000000003633c10] [c00000000206a2e8] dax_pmem_init+0x34/0x48 > [c000000003633c30] [c0000000000132d0] do_one_initcall+0x60/0x320 > [c000000003633d00] [c0000000020051b0] kernel_init_freeable+0x360/0x400 > [c000000003633de0] [c000000000013764] kernel_init+0x34/0x1d0 > [c000000003633e50] [c00000000000de14] ret_from_kernel_thread+0x5c/0x64 > > Fixes: c4386bd8ee3a ("mm/memremap: add ZONE_DEVICE support for compound pages") > Cc: Joao Martins > Cc: Muchun Song > Cc: Dan Williams > Reported-by: Tarun Sahu > Signed-off-by: Aneesh Kumar K.V Looks good to me, Reviewed-by: Dan Williams ...I guess device-dax is not often used on ppc if this has been lingering since v5.17.