On Fri, Aug 26, 2022 at 12:49:37PM +0200, David Hildenbrand wrote: > 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? IMHO they're not needed? The rule is simple in my mind: we should only pass in a pfn-typed swap entry into pfn_swap_entry_to_page() (or the new swp_offset_pfn()), or it's a violation of the API. In these two cases they do not violate the API and they're always safe because they're guaranteed to be pfn swap entries when calling. Thanks, -- Peter Xu
