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identity=mailfrom; envelope-from=""; helo=NAM10-MW2-obe.outbound.protection.outlook.com; client-ip=40.107.94.68 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617132758-944492 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 Fri, Mar 26, 2021 at 11:08:02AM +1100, Alistair Popple wrote: > diff --git a/mm/memory.c b/mm/memory.c > index 3a5705cfc891..33d11527ef77 100644 > +++ b/mm/memory.c > @@ -781,6 +781,27 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pte = pte_swp_mkuffd_wp(pte); > set_pte_at(src_mm, addr, src_pte, pte); > } > + } else if (is_device_exclusive_entry(entry)) { > + page = pfn_swap_entry_to_page(entry); > + > + get_page(page); > + rss[mm_counter(page)]++; > + > + if (is_writable_device_exclusive_entry(entry) && > + is_cow_mapping(vm_flags)) { > + /* > + * COW mappings require pages in both > + * parent and child to be set to read. > + */ > + entry = make_readable_device_exclusive_entry( > + swp_offset(entry)); > + pte = swp_entry_to_pte(entry); > + if (pte_swp_soft_dirty(*src_pte)) > + pte = pte_swp_mksoft_dirty(pte); > + if (pte_swp_uffd_wp(*src_pte)) > + pte = pte_swp_mkuffd_wp(pte); > + set_pte_at(src_mm, addr, src_pte, pte); > + } This needs to have the same logic as we now have in copy_present_page(). The page *is* present and we can't copy the PTE value hidden in a swap entry if we can't copy the PTE normally. The code should be shared because nobody is going to remember about this corner case. Jason