linux-ext4 - [PATCH v1 04/15] mm: add device coherent checker to remove migration pte

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Date:   Thu, 5 May 2022 16:34:27 -0500
From:   Alex Sierra <alex.sierra@....com>
To:     <jgg@...dia.com>
CC:     <david@...hat.com>, <Felix.Kuehling@....com>, <linux-mm@...ck.org>,
        <rcampbell@...dia.com>, <linux-ext4@...r.kernel.org>,
        <linux-xfs@...r.kernel.org>, <amd-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <hch@....de>,
        <jglisse@...hat.com>, <apopple@...dia.com>, <willy@...radead.org>,
        <akpm@...ux-foundation.org>
Subject: [PATCH v1 04/15] mm: add device coherent checker to remove migration pte

During remove_migration_pte(), entries for device coherent type pages
that were not created through special migration ptes, ignore _PAGE_RW
flag. This path can be found at migrate_device_page(), where valid
vma is not required. In this case, migrate_vma_collect_pmd() is not
called and special migration ptes are not set.

Signed-off-by: Alex Sierra <alex.sierra@....com>
---
 mm/migrate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 6c31ee1e1c9b..e18ddee56f37 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -206,7 +206,8 @@ static bool remove_migration_pte(struct folio *folio,
 		 * Recheck VMA as permissions can change since migration started
 		 */
 		entry = pte_to_swp_entry(*pvmw.pte);
-		if (is_writable_migration_entry(entry))
+		if (is_writable_migration_entry(entry) ||
+		    is_device_coherent_page(pfn_to_page(pvmw.pfn)))
 			pte = maybe_mkwrite(pte, vma);
 		else if (pte_swp_uffd_wp(*pvmw.pte))
 			pte = pte_mkuffd_wp(pte);
-- 
2.32.0