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03dfee6d5f
Recently in commitf6eedbba7a("powerpc/mm/hash: Increase VA range to 128TB"), we increased H_PGD_INDEX_SIZE to 15 when we're building with 64K pages. This makes it larger than RADIX_PGD_INDEX_SIZE (13), which means the logic to calculate MAX_PGD_INDEX_SIZE in book3s/64/pgtable.h is wrong. The end result is that the PGD (Page Global Directory, ie top level page table) of the kernel (aka. swapper_pg_dir), is too small. This generally doesn't lead to a crash, as we don't use the full range in normal operation. However if we try to dump the kernel pagetables we can trigger a crash because we walk off the end of the pgd into other memory and eventually try to dereference something bogus: $ cat /sys/kernel/debug/kernel_pagetables Unable to handle kernel paging request for data at address 0xe8fece0000000000 Faulting instruction address: 0xc000000000072314 cpu 0xc: Vector: 380 (Data SLB Access) at [c0000000daa13890] pc: c000000000072314: ptdump_show+0x164/0x430 lr: c000000000072550: ptdump_show+0x3a0/0x430 dar: e802cf0000000000 seq_read+0xf8/0x560 full_proxy_read+0x84/0xc0 __vfs_read+0x6c/0x1d0 vfs_read+0xbc/0x1b0 SyS_read+0x6c/0x110 system_call+0x38/0xfc The root cause is that MAX_PGD_INDEX_SIZE isn't actually computed to be the max of H_PGD_INDEX_SIZE or RADIX_PGD_INDEX_SIZE. To fix that move the calculation into asm-offsets.c where we can do it easily using max(). Fixes:f6eedbba7a("powerpc/mm/hash: Increase VA range to 128TB") Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.