linux-kernel - [PATCH v2 07/17] mm/page_vma_mapped: device-exclusive entries are not migration entries

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Message-ID: <20250210193801.781278-8-david@redhat.com>
Date: Mon, 10 Feb 2025 20:37:49 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-doc@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linux-mm@...ck.org,
	nouveau@...ts.freedesktop.org,
	linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	damon@...ts.linux.dev,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jérôme Glisse <jglisse@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Alex Shi <alexs@...nel.org>,
	Yanteng Si <si.yanteng@...ux.dev>,
	Karol Herbst <kherbst@...hat.com>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...nel.org>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	SeongJae Park <sj@...nel.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jann Horn <jannh@...gle.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Peter Xu <peterx@...hat.com>,
	Alistair Popple <apopple@...dia.com>,
	Jason Gunthorpe <jgg@...dia.com>
Subject: [PATCH v2 07/17] mm/page_vma_mapped: device-exclusive entries are not migration entries

It's unclear why they would be considered migration entries; they are
not.

Likely we'll never really trigger that case in practice, because
migration (including folio split) of a folio that has device-exclusive
entries is never started, as we would detect "additional references":
device-exclusive entries adjust the mapcount, but not the refcount.

Fixes: b756a3b5e7ea ("mm: device exclusive memory access")
Reviewed-by: Alistair Popple <apopple@...dia.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/page_vma_mapped.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 81839a9e74f16..32679be22d30c 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -111,8 +111,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
 			return false;
 		entry = pte_to_swp_entry(ptent);
 
-		if (!is_migration_entry(entry) &&
-		    !is_device_exclusive_entry(entry))
+		if (!is_migration_entry(entry))
 			return false;
 
 		pfn = swp_offset_pfn(entry);
-- 
2.48.1