On Fri, Jun 07, 2024 at 02:23:53PM +0200, David Hildenbrand wrote: > Relying on the mapcount for non-present PTEs that reference pages > doesn't make any sense: they are not accounted in the mapcount, so > page_mapcount() == 1 won't return the result we actually want to know. > > While we don't check the mapcount for migration entries already, we > could end up checking it for swap, hwpoison, device exclusive, ... > entries, which we really shouldn't. > > There is one exception: device private entries, which we consider > fake-present (e.g., incremented the mapcount). But we won't care about > that for now for PM_MMAP_EXCLUSIVE, because indicating PM_SWAP for them > although they are fake-present already sounds suspiciously wrong. > > Let's never indicate PM_MMAP_EXCLUSIVE without PM_PRESENT. > > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Forgot to comment on something: > @@ -1517,14 +1514,13 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, > if (pmd_swp_uffd_wp(pmd)) > flags |= PM_UFFD_WP; > VM_BUG_ON(!is_pmd_migration_entry(pmd)); > - migration = is_migration_entry(entry); > page = pfn_swap_entry_to_page(entry); We do not really need to get the page anymore here as that is the non-present part. Then we could get away without checking the flags as only page != NULL would mean a present pmd. Not that we gain much as this is far from being a hot-path, but just saying.. -- Oscar Salvador SUSE Labs
