Re: [PATCH v2] mm: re-allow pinning of zero pfns (again)

Andrew Morton
2022-08-28T01:40:26Z

On Sat, 27 Aug 2022 17:59:32 -0700 John Hubbard <jhubbard@nvidia.com> wrote:

>
> /* The zero page is always allowed to be pinned. */

Wow, that's really verbose :)

--- a/include/linux/mm.h~mm-re-allow-pinning-of-zero-pfns-again-fix
+++ a/include/linux/mm.h
@@ -1544,11 +1544,7 @@ static inline bool is_longterm_pinnable_
if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
return false;
#endif
- /*
- * The zero page might reside in a movable zone, however it may not
- * be migrated and can therefore be pinned. The vfio subsystem pins
- * user mappings including the zero page for IOMMU translation.
- */
+ /* The zero page may always be pinned */
if (is_zero_pfn(page_to_pfn(page)))
return true;

_