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From:   Ralph Campbell <rcampbell@nvidia.com>
To:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
CC:     Jerome Glisse <jglisse@redhat.com>,
        Alistair Popple <apopple@nvidia.com>,
        Christoph Hellwig <hch@lst.de>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Bharata B Rao <bharata@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ralph Campbell <rcampbell@nvidia.com>
Subject: [PATCH 2/2] mm/migrate: preserve soft dirty in remove_migration_pte()
Date:   Mon, 31 Aug 2020 14:22:22 -0700
Message-ID: <20200831212222.22409-3-rcampbell@nvidia.com>
In-Reply-To: <20200831212222.22409-1-rcampbell@nvidia.com>
References: <20200831212222.22409-1-rcampbell@nvidia.com>
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The code to remove a migration PTE and replace it with a device private
PTE was not copying the soft dirty bit from the migration entry.
This could lead to page contents not being marked dirty when faulting
the page back from device private memory.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
---
 mm/migrate.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index fe339a847328..4f89360d9e77 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -249,6 +249,8 @@ static bool remove_migration_pte(struct page *page, str=
uct vm_area_struct *vma,
 		if (unlikely(is_device_private_page(new))) {
 			entry =3D make_device_private_entry(new, pte_write(pte));
 			pte =3D swp_entry_to_pte(entry);
+			if (pte_swp_soft_dirty(*pvmw.pte))
+				pte =3D pte_swp_mksoft_dirty(pte);
 			if (pte_swp_uffd_wp(*pvmw.pte))
 				pte =3D pte_swp_mkuffd_wp(pte);
 		}
--=20
2.20.1