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commit 36b78402d97a3b9aeab136feb9b00d8647ec2c20 upstream. H_PAGE_THP_HUGE is used to differentiate between a THP hugepage and hugetlb hugepage entries. The difference is WRT how we handle hash fault on these address. THP address enables MPSS in segments. We want to manage devmap hugepage entries similar to THP pt entries. Hence use H_PAGE_THP_HUGE for devmap huge PTE entries. With current code while handling hash PTE fault, we do set is_thp = true when finding devmap PTE huge PTE entries. Current code also does the below sequence we setting up huge devmap entries. entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); if (pfn_t_devmap(pfn)) entry = pmd_mkdevmap(entry); In that case we would find both H_PAGE_THP_HUGE and PAGE_DEVMAP set for huge devmap PTE entries. This results in false positive error like below. kernel BUG at /home/kvaneesh/src/linux/mm/memory.c:4321! Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Modules linked in: CPU: 56 PID: 67996 Comm: t_mmap_dio Not tainted 5.6.0-rc4-59640-g371c804dedbc #128 .... NIP [c00000000044c9e4] __follow_pte_pmd+0x264/0x900 LR [c0000000005d45f8] dax_writeback_one+0x1a8/0x740 Call Trace: str_spec.74809+0x22ffb4/0x2d116c (unreliable) dax_writeback_one+0x1a8/0x740 dax_writeback_mapping_range+0x26c/0x700 ext4_dax_writepages+0x150/0x5a0 do_writepages+0x68/0x180 __filemap_fdatawrite_range+0x138/0x180 file_write_and_wait_range+0xa4/0x110 ext4_sync_file+0x370/0x6e0 vfs_fsync_range+0x70/0xf0 sys_msync+0x220/0x2e0 system_call+0x5c/0x68 This is because our pmd_trans_huge check doesn't exclude _PAGE_DEVMAP. To make this all consistent, update pmd_mkdevmap to set H_PAGE_THP_HUGE and pmd_trans_huge check now excludes _PAGE_DEVMAP correctly. Fixes: ebd31197931d ("powerpc/mm: Add devmap support for ppc64") Cc: stable@vger.kernel.org # v4.13+ Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200313094842.351830-1-aneesh.kumar@linux.ibm.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.