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charset="UTF-8" X-Rspamd-Queue-Id: 2994880005 X-Stat-Signature: c8r755td3zut66yrrxa3hifxmfxfk3mw X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1670452846-408029 X-HE-Meta: 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 XR4C9dM0 iTEB5adRZdfOZgmUeAXbNlHLGmYIgFY19eGBBe8gAI1SYZvLuhtbL7J9E3yqTbrJDtbvE1A8ErL+4yiwinkcHh3wgKfzdkwv7d/Ye X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Dec 6, 2022 at 2:57 AM David Hildenbrand wrote: > > 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. Thanks for debugging this. IIUC this means even swap is actually broken on x86_32 + PAE? > > 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. > > Fixes: 0d206b5d2e0d ("mm/swap: add swp_offset_pfn() to fetch PFN from swap entry") > Cc: Andrew Morton > Cc: Peter Xu > Cc: Yang Shi > Cc: Hugh Dickins > Cc: Andrea Arcangeli > Signed-off-by: David Hildenbrand > --- > > v1 -> v2: > * Rely on sizeof(phys_addr_t) and min_t() instead. > * Survives my various cross compilations and testing on x86 PAE. Reviewed-by: Yang Shi > > --- > include/linux/swapops.h | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/include/linux/swapops.h b/include/linux/swapops.h > index 86b95ccb81bb..424d586ed1ca 100644 > --- a/include/linux/swapops.h > +++ b/include/linux/swapops.h > @@ -33,11 +33,13 @@ > * can use the extra bits to store other information besides PFN. > */ > #ifdef MAX_PHYSMEM_BITS > -#define SWP_PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT) > +#define SWP_PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT) > #else /* MAX_PHYSMEM_BITS */ > -#define SWP_PFN_BITS (BITS_PER_LONG - PAGE_SHIFT) > +#define SWP_PFN_BITS min_t(phys_addr_t, \ > + sizeof(phys_addr_t) * 8 - PAGE_SHIFT, \ > + SWP_TYPE_SHIFT) > #endif /* MAX_PHYSMEM_BITS */ > -#define SWP_PFN_MASK (BIT(SWP_PFN_BITS) - 1) > +#define SWP_PFN_MASK (BIT(SWP_PFN_BITS) - 1) > > /** > * Migration swap entry specific bitfield definitions. Layout: > > base-commit: 76dcd734eca23168cb008912c0f69ff408905235 > -- > 2.38.1 >