linux-kernel - [PATCH] mm: re-allow pinning of zero pfns (again)

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Date:   Mon, 08 Aug 2022 22:42:24 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     alex.sierra@....com, akpm@...ux-foundation.org
Cc:     hch@....de, Felix.Kuehling@....com, apopple@...dia.com,
        david@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm: re-allow pinning of zero pfns (again)

The below referenced commit makes the same error as 1c563432588d ("mm: fix
is_pinnable_page against a cma page"), re-interpreting the logic to exclude
pinning of the zero page, which breaks device assignment with vfio.

Link: https://lore.kernel.org/all/165490039431.944052.12458624139225785964.stgit@omen
Fixes: f25cbb7a95a2 ("mm: add zone device coherent type memory support")
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---
 include/linux/mm.h |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 18e01474cf6b..772279ed7010 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1544,9 +1544,8 @@ static inline bool is_longterm_pinnable_page(struct page *page)
 	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
 		return false;
 #endif
-	return !(is_device_coherent_page(page) ||
-		 is_zone_movable_page(page) ||
-		 is_zero_pfn(page_to_pfn(page)));
+	return !(is_device_coherent_page(page) || is_zone_movable_page(page)) ||
+	       is_zero_pfn(page_to_pfn(page));
 }
 #else
 static inline bool is_longterm_pinnable_page(struct page *page)