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From: Alistair Popple <apopple@nvidia.com>
To: <linux-mm@kvack.org>, <nouveau@lists.freedesktop.org>,
	<bskeggs@redhat.com>, <akpm@linux-foundation.org>
Cc: rcampbell@nvidia.com, linux-doc@vger.kernel.org,
	Alistair Popple <apopple@nvidia.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	kvm-ppc@vger.kernel.org
Subject: [Nouveau] [PATCH 1/9] mm/migrate.c: Always allow device private pages to migrate
Date: Tue, 9 Feb 2021 12:07:14 +1100
Message-ID: <20210209010722.13839-2-apopple@nvidia.com> (raw)
In-Reply-To: <20210209010722.13839-1-apopple@nvidia.com>

Device private pages are used to represent device memory that is not
directly accessible from the CPU. Extra references to a device private
page are only used to ensure the struct page itself remains valid whilst
waiting for migration entries. Therefore extra references should not
prevent device private page migration as this can lead to failures to
migrate pages back to the CPU which are fatal to the user process.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 mm/migrate.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 20ca887ea769..053228559fd3 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -405,8 +405,13 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	int nr = thp_nr_pages(page);
 
 	if (!mapping) {
-		/* Anonymous page without mapping */
-		if (page_count(page) != expected_count)
+		/*
+		 * Anonymous page without mapping. Device private pages should
+		 * never have extra references except during migration, but it
+		 * is safe to ignore these.
+		 */
+		if (!is_device_private_page(page) &&
+			page_count(page) != expected_count)
 			return -EAGAIN;
 
 		/* No turning back from here */
-- 
2.20.1

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Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09  1:07 [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau Alistair Popple
2021-02-09  1:07 ` Alistair Popple [this message]
2021-02-09 13:39   ` [Nouveau] [PATCH 1/9] mm/migrate.c: Always allow device private pages to migrate Jason Gunthorpe
2021-02-10  3:40     ` Alistair Popple
2021-02-10 12:56       ` Jason Gunthorpe
2021-02-09  1:07 ` [Nouveau] [PATCH 2/9] mm/migrate.c: Allow pfn flags to be passed to migrate_vma_setup() Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 3/9] mm/migrate: Add a unmap and pin migration mode Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 4/9] Documentation: Add unmap and pin to HMM Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 5/9] hmm-tests: Add test for unmap and pin Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 6/9] nouveau/dmem: Only map migrating pages Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 7/9] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 8/9] nouveau/dmem: Add support for multiple page types Alistair Popple
2021-02-09  1:07 ` [Nouveau] [PATCH 9/9] nouveau/svm: Implement atomic SVM access Alistair Popple
2021-02-09 10:27 ` [Nouveau] [PATCH 0/9] Add support for SVM atomics in Nouveau Daniel Vetter
2021-02-09 12:57   ` Alistair Popple
2021-02-09 13:35     ` Jason Gunthorpe
2021-02-09 13:39       ` Daniel Vetter
2021-02-09 13:44         ` Jason Gunthorpe
2021-02-09 21:17       ` Jerome Glisse
2021-02-10 17:56         ` Jason Gunthorpe
2021-02-09 13:37     ` Daniel Vetter
2021-02-09 20:53       ` John Hubbard
2021-02-10 12:59         ` Daniel Vetter
2021-02-11  2:26           ` John Hubbard
2021-02-10 17:59         ` Jason Gunthorpe
2021-02-11  7:55           ` Christoph Hellwig
2021-02-17 23:00             ` Alistair Popple

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