+ mm-re-allow-pinning-of-zero-pfns-again.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: re-allow pinning of zero pfns (again)
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-re-allow-pinning-of-zero-pfns-again.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-re-allow-pinning-of-zero-pfns-again.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alex Williamson <alex.williamson@redhat.com>
Subject: mm: re-allow pinning of zero pfns (again)
Date: Wed, 10 Aug 2022 10:53:59 -0600

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.

To avoid further subtle mistakes, split the logic into discrete tests.

Link: https://lkml.kernel.org/r/166015037385.760108.16881097713975517242.stgit@omen
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@redhat.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Suggested-by: Felix Kuehling <felix.kuehling@amd.com>
Cc: Alex Sierra <alex.sierra@amd.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

--- a/include/linux/mm.h~mm-re-allow-pinning-of-zero-pfns-again
+++ a/include/linux/mm.h
@@ -1544,9 +1544,20 @@ static inline bool is_longterm_pinnable_
 	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)));
+	/*
+	 * 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.
+	 */
+	if (is_zero_pfn(page_to_pfn(page)))
+		return true;
+
+	/* Coherent device memory must always allow eviction. */
+	if (is_device_coherent_page(page))
+		return false;
+
+	/* Otherwise, non-movable zone pages can be pinned. */
+	return !is_zone_movable_page(page);
 }
 #else
 static inline bool is_longterm_pinnable_page(struct page *page)
_

Patches currently in -mm which might be from alex.williamson@redhat.com are

mm-re-allow-pinning-of-zero-pfns-again.patch