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>
projects / platform / kernel / linux-starfive.git / commitdiff