On Tuesday, 23 March 2021 9:26:43 PM AEDT David Hildenbrand wrote: > On 20.03.21 10:36, Miaohe Lin wrote: > > If the zone device page does not belong to un-addressable device memory, > > the variable entry will be uninitialized and lead to indeterminate pte > > entry ultimately. Fix this unexpectant case and warn about it. > > s/unexpectant/unexpected/ > > > > > Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache coherent with CPU") > > Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> > > --- > > mm/migrate.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 20a3bf75270a..271081b014cb 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -2972,6 +2972,13 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate, > > > > swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE); > > entry = swp_entry_to_pte(swp_entry); > > + } else { > > + /* > > + * For now we only support migrating to un-addressable > > + * device memory. > > + */ > > + WARN_ON(1); > > + goto abort; > > Fix it by crashing the kernel with panic_on_warn? :) > > If this case can actual happen, than no WARN_ON() - rather a > pr_warn_once(). If this case cannot happen, why do we even care (it's > not a fix then)? There is also already a check for this case in migrate_vma_pages(). The problem is it happens after the call to migrate_vma_insert_page(). I wonder if instead it would be better just to move the existing check to before that call?