630dc25e43
We use "unsigned long" to store a PFN in the kernel and phys_addr_t to store a physical address. On a 64bit system, both are 64bit wide. However, on a 32bit system, the latter might be 64bit wide. This is, for example, the case on x86 with PAE: phys_addr_t and PTEs are 64bit wide, while "unsigned long" only spans 32bit. The current definition of SWP_PFN_BITS without MAX_PHYSMEM_BITS misses that case, and assumes that the maximum PFN is limited by an 32bit phys_addr_t. This implies, that SWP_PFN_BITS will currently only be able to cover 4 GiB - 1 on any 32bit system with 4k page size, which is wrong. Let's rely on the number of bits in phys_addr_t instead, but make sure to not exceed the maximum swap offset, to not make the BUILD_BUG_ON() in is_pfn_swap_entry() unhappy. Note that swp_entry_t is effectively an unsigned long and the maximum swap offset shares that value with the swap type. For example, on an 8 GiB x86 PAE system with a kernel config based on Debian 11.5 (-> CONFIG_FLATMEM=y, CONFIG_X86_PAE=y), we will currently fail removing migration entries (remove_migration_ptes()), because mm/page_vma_mapped.c:check_pte() will fail to identify a PFN match as swp_offset_pfn() wrongly masks off PFN bits. For example, split_huge_page_to_list()->...->remap_page() will leave migration entries in place and continue to unlock the page. Later, when we stumble over these migration entries (e.g., via /proc/self/pagemap), pfn_swap_entry_to_page() will BUG_ON() because these migration entries shouldn't exist anymore and the page was unlocked. [ 33.067591] kernel BUG at include/linux/swapops.h:497! [ 33.067597] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI [ 33.067602] CPU: 3 PID: 742 Comm: cow Tainted: G E 6.1.0-rc8+ #16 [ 33.067605] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014 [ 33.067606] EIP: pagemap_pmd_range+0x644/0x650 [ 33.067612] Code: 00 00 00 00 66 90 89 ce b9 00 f0 ff ff e9 ff fb ff ff 89 d8 31 db e8 48 c6 52 00 e9 23 fb ff ff e8 61 83 56 00 e9 b6 fe ff ff <0f> 0b bf 00 f0 ff ff e9 38 fa ff ff 3e 8d 74 26 00 55 89 e5 57 31 [ 33.067615] EAX: ee394000 EBX: 00000002 ECX: ee394000 EDX: 00000000 [ 33.067617] ESI: c1b0ded4 EDI: 00024a00 EBP: c1b0ddb4 ESP: c1b0dd68 [ 33.067619] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00010246 [ 33.067624] CR0: 80050033 CR2: b7a00000 CR3: 01bbbd20 CR4: 00350ef0 [ 33.067625] Call Trace: [ 33.067628] ? madvise_free_pte_range+0x720/0x720 [ 33.067632] ? smaps_pte_range+0x4b0/0x4b0 [ 33.067634] walk_pgd_range+0x325/0x720 [ 33.067637] ? mt_find+0x1d6/0x3a0 [ 33.067641] ? mt_find+0x1d6/0x3a0 [ 33.067643] __walk_page_range+0x164/0x170 [ 33.067646] walk_page_range+0xf9/0x170 [ 33.067648] ? __kmem_cache_alloc_node+0x2a8/0x340 [ 33.067653] pagemap_read+0x124/0x280 [ 33.067658] ? default_llseek+0x101/0x160 [ 33.067662] ? smaps_account+0x1d0/0x1d0 [ 33.067664] vfs_read+0x90/0x290 [ 33.067667] ? do_madvise.part.0+0x24b/0x390 [ 33.067669] ? debug_smp_processor_id+0x12/0x20 [ 33.067673] ksys_pread64+0x58/0x90 [ 33.067675] __ia32_sys_ia32_pread64+0x1b/0x20 [ 33.067680] __do_fast_syscall_32+0x4c/0xc0 [ 33.067683] do_fast_syscall_32+0x29/0x60 [ 33.067686] do_SYSENTER_32+0x15/0x20 [ 33.067689] entry_SYSENTER_32+0x98/0xf1 Decrease the indentation level of SWP_PFN_BITS and SWP_PFN_MASK to keep it readable and consistent. [david@redhat.com: rely on sizeof(phys_addr_t) and min_t() instead] Link: https://lkml.kernel.org/r/20221206105737.69478-1-david@redhat.com [david@redhat.com: use "int" for comparison, as we're only comparing numbers < 64] Link: https://lkml.kernel.org/r/1f157500-2676-7cef-a84e-9224ed64e540@redhat.com Link: https://lkml.kernel.org/r/20221205150857.167583-1-david@redhat.com Fixes: 0d206b5d2e0d ("mm/swap: add swp_offset_pfn() to fetch PFN from swap entry") Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Reviewed-by: Yang Shi <shy828301@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.