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Subject: [PATCH] mm: Re-allow pinning of zero pfns
From:   Alex Williamson <alex.williamson@redhat.com>
To:     akpm@linux-foundation.org, minchan@kernel.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        paulmck@kernel.org, jhubbard@nvidia.com, joaodias@google.com,
        jgg@ziepe.ca, david@redhat.com
Date:   Fri, 10 Jun 2022 16:35:13 -0600
Message-ID: <165490039431.944052.12458624139225785964.stgit@omen>
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The commit referenced below subtly and inadvertently changed the logic
to disallow pinning of zero pfns.  This breaks device assignment with
vfio and potentially various other users of gup.  Exclude the zero page
test from the negation.

Fixes: 1c563432588d ("mm: fix is_pinnable_page against a cma page")
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

At least I assume this was inadvertent...  If there's a better fix,
please run with it as I'm out of the office the 1st half of next
week and would like to see this fixed ASAP.  Thanks!

 include/linux/mm.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bc8f326be0ce..781fae17177d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1600,7 +1600,7 @@ static inline bool is_pinnable_page(struct page *page)
 	if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
 		return false;
 #endif
-	return !(is_zone_movable_page(page) || is_zero_pfn(page_to_pfn(page)));
+	return !is_zone_movable_page(page) || is_zero_pfn(page_to_pfn(page));
 }
 #else
 static inline bool is_pinnable_page(struct page *page)