On 24.08.22 00:11, Peter Xu wrote: > Yu Zhao reported a bug after the commit "mm/swap: Add swp_offset_pfn() to > fetch PFN from swap entry" added a check in swp_offset_pfn() for swap type [1]: > > kernel BUG at include/linux/swapops.h:117! > CPU: 46 PID: 5245 Comm: EventManager_De Tainted: G S O L 6.0.0-dbg-DEV #2 > RIP: 0010:pfn_swap_entry_to_page+0x72/0xf0 > Code: c6 48 8b 36 48 83 fe ff 74 53 48 01 d1 48 83 c1 08 48 8b 09 f6 > c1 01 75 7b 66 90 48 89 c1 48 8b 09 f6 c1 01 74 74 5d c3 eb 9e <0f> 0b > 48 ba ff ff ff ff 03 00 00 00 eb ae a9 ff 0f 00 00 75 13 48 > RSP: 0018:ffffa59e73fabb80 EFLAGS: 00010282 > RAX: 00000000ffffffe8 RBX: 0c00000000000000 RCX: ffffcd5440000000 > RDX: 1ffffffffff7a80a RSI: 0000000000000000 RDI: 0c0000000000042b > RBP: ffffa59e73fabb80 R08: ffff9965ca6e8bb8 R09: 0000000000000000 > R10: ffffffffa5a2f62d R11: 0000030b372e9fff R12: ffff997b79db5738 > R13: 000000000000042b R14: 0c0000000000042b R15: 1ffffffffff7a80a > FS: 00007f549d1bb700(0000) GS:ffff99d3cf680000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000440d035b3180 CR3: 0000002243176004 CR4: 00000000003706e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > change_pte_range+0x36e/0x880 > change_p4d_range+0x2e8/0x670 > change_protection_range+0x14e/0x2c0 > mprotect_fixup+0x1ee/0x330 > do_mprotect_pkey+0x34c/0x440 > __x64_sys_mprotect+0x1d/0x30 > > It triggers because pfn_swap_entry_to_page() could be called upon e.g. a > genuine swap entry. > > Fix it by only calling it when it's a write migration entry where the page* > is used. > > [1] https://lore.kernel.org/lkml/CAOUHufaVC2Za-p8m0aiHw6YkheDcrO-C3wRGixwDS32VTS+k1w@xxxxxxxxxxxxxx/ > > Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Reported-by: Yu Zhao <yuzhao@xxxxxxxxxx> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > --- > mm/mprotect.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index f2b9b1da9083..4549f5945ebe 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -203,10 +203,11 @@ static unsigned long change_pte_range(struct mmu_gather *tlb, > pages++; > } else if (is_swap_pte(oldpte)) { > swp_entry_t entry = pte_to_swp_entry(oldpte); > - struct page *page = pfn_swap_entry_to_page(entry); > pte_t newpte; > > if (is_writable_migration_entry(entry)) { > + struct page *page = pfn_swap_entry_to_page(entry); > + > /* > * A protection check is difficult so > * just be safe and disable write Stumbling over the THP code, I was wondering if we also want to adjust change_huge_pmd() and hugetlb_change_protection. There are no actual swap entries, so I assume we're fine. diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 482c1826e723..466364e7fc5f 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1798,10 +1798,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION if (is_swap_pmd(*pmd)) { swp_entry_t entry = pmd_to_swp_entry(*pmd); - struct page *page = pfn_swap_entry_to_page(entry); VM_BUG_ON(!is_pmd_migration_entry(*pmd)); if (is_writable_migration_entry(entry)) { + struct page *page = pfn_swap_entry_to_page(entry); pmd_t newpmd; /* * A protection check is difficult so diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2480ba627aa5..559465fae5cd 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6370,9 +6370,9 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, } if (unlikely(is_hugetlb_entry_migration(pte))) { swp_entry_t entry = pte_to_swp_entry(pte); - struct page *page = pfn_swap_entry_to_page(entry); if (!is_readable_migration_entry(entry)) { + struct page *page = pfn_swap_entry_to_page(entry); pte_t newpte; if (PageAnon(page)) @Peter, what's your thought? -- Thanks, David / dhildenb
