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

[Andrew Morton]

On Sat, 27 Aug 2022 17:59:32 -0700 John Hubbard <jhubbard@xxxxxxxxxx> 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;
 
_