Alex Sierra alex.sierra@amd.com writes:
[...]
diff --git a/mm/rmap.c b/mm/rmap.c index fedb82371efe..d57102cd4b43 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1995,7 +1995,8 @@ void try_to_migrate(struct folio *folio, enum ttu_flags flags) TTU_SYNC))) return;
- if (folio_is_zone_device(folio) && !folio_is_device_private(folio))
if (folio_is_zone_device(folio) &&
(!folio_is_device_private(folio) && !folio_is_device_coherent(folio)))return;
/*
I vaguely recall commenting on this previously, or at least intending to. In try_to_migrate_one() we have this:
if (folio_is_zone_device(folio)) { unsigned long pfn = folio_pfn(folio); swp_entry_t entry; pte_t swp_pte;
/* * Store the pfn of the page in a special migration * pte. do_swap_page() will wait until the migration * pte is removed and then restart fault handling. */ entry = pte_to_swp_entry(pteval); if (is_writable_device_private_entry(entry)) entry = make_writable_migration_entry(pfn); else entry = make_readable_migration_entry(pfn); swp_pte = swp_entry_to_pte(entry);
The check in try_to_migrate() guarantees that if folio_is_zone_device() is true this must be a DEVICE_PRIVATE page and it treats it as such by assuming there is a special device private swap entry there.
Relying on that assumption seems bad, and I have no idea why I didn't just use is_device_private_page() originally but I think the fix is just to change this to:
if (folio_is_device_private(folio))
And let DEVICE_COHERENT pages fall through to normal page processing.
- Alistair