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Message-ID: <20260111205820.830410-3-francois.dugast@intel.com>
Date: Sun, 11 Jan 2026 21:55:41 +0100
From: Francois Dugast <francois.dugast@...el.com>
To: intel-xe@...ts.freedesktop.org
Cc: dri-devel@...ts.freedesktop.org,
Matthew Brost <matthew.brost@...el.com>,
Zi Yan <ziy@...dia.com>,
David Hildenbrand <david@...nel.org>,
Oscar Salvador <osalvador@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Balbir Singh <balbirs@...dia.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Alistair Popple <apopple@...dia.com>,
linux-mm@...ck.org,
linux-cxl@...r.kernel.org,
linux-kernel@...r.kernel.org,
Francois Dugast <francois.dugast@...el.com>
Subject: [PATCH v4 2/7] mm/zone_device: Add free_zone_device_folio_prepare() helper
From: Matthew Brost <matthew.brost@...el.com>
Add free_zone_device_folio_prepare(), a helper that restores large
ZONE_DEVICE folios to a sane, initial state before freeing them.
Compound ZONE_DEVICE folios overwrite per-page state (e.g. pgmap and
compound metadata). Before returning such pages to the device pgmap
allocator, each constituent page must be reset to a standalone
ZONE_DEVICE folio with a valid pgmap and no compound state.
Use this helper prior to folio_free() for device-private and
device-coherent folios to ensure consistent device page state for
subsequent allocations.
Fixes: d245f9b4ab80 ("mm/zone_device: support large zone device private folios")
Cc: Zi Yan <ziy@...dia.com>
Cc: David Hildenbrand <david@...nel.org>
Cc: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Balbir Singh <balbirs@...dia.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Liam R. Howlett <Liam.Howlett@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Rapoport <rppt@...nel.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Alistair Popple <apopple@...dia.com>
Cc: linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Suggested-by: Alistair Popple <apopple@...dia.com>
Signed-off-by: Matthew Brost <matthew.brost@...el.com>
Signed-off-by: Francois Dugast <francois.dugast@...el.com>
---
include/linux/memremap.h | 1 +
mm/memremap.c | 55 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 56 insertions(+)
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 97fcffeb1c1e..88e1d4707296 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -230,6 +230,7 @@ static inline bool is_fsdax_page(const struct page *page)
#ifdef CONFIG_ZONE_DEVICE
void zone_device_page_init(struct page *page, unsigned int order);
+void free_zone_device_folio_prepare(struct folio *folio);
void *memremap_pages(struct dev_pagemap *pgmap, int nid);
void memunmap_pages(struct dev_pagemap *pgmap);
void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
diff --git a/mm/memremap.c b/mm/memremap.c
index 39dc4bd190d0..375a61e18858 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -413,6 +413,60 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn)
}
EXPORT_SYMBOL_GPL(get_dev_pagemap);
+/**
+ * free_zone_device_folio_prepare() - Prepare a ZONE_DEVICE folio for freeing.
+ * @folio: ZONE_DEVICE folio to prepare for release.
+ *
+ * ZONE_DEVICE pages/folios (e.g., device-private memory or fsdax-backed pages)
+ * can be compound. When freeing a compound ZONE_DEVICE folio, the tail pages
+ * must be restored to a sane ZONE_DEVICE state before they are released.
+ *
+ * This helper:
+ * - Clears @folio->mapping and, for compound folios, clears each page's
+ * compound-head state (ClearPageHead()/clear_compound_head()).
+ * - Resets the compound order metadata (folio_reset_order()) and then
+ * initializes each constituent page as a standalone ZONE_DEVICE folio:
+ * * clears ->mapping
+ * * restores ->pgmap (prep_compound_page() overwrites it)
+ * * clears ->share (only relevant for fsdax; unused for device-private)
+ *
+ * If @folio is order-0, only the mapping is cleared and no further work is
+ * required.
+ */
+void free_zone_device_folio_prepare(struct folio *folio)
+{
+ struct dev_pagemap *pgmap = page_pgmap(&folio->page);
+ int order, i;
+
+ VM_WARN_ON_FOLIO(!folio_is_zone_device(folio), folio);
+
+ folio->mapping = NULL;
+ order = folio_order(folio);
+ if (!order)
+ return;
+
+ folio_reset_order(folio);
+
+ for (i = 0; i < (1UL << order); i++) {
+ struct page *page = folio_page(folio, i);
+ struct folio *new_folio = (struct folio *)page;
+
+ ClearPageHead(page);
+ clear_compound_head(page);
+
+ new_folio->mapping = NULL;
+ /*
+ * Reset pgmap which was over-written by
+ * prep_compound_page().
+ */
+ new_folio->pgmap = pgmap;
+ new_folio->share = 0; /* fsdax only, unused for device private */
+ VM_WARN_ON_FOLIO(folio_ref_count(new_folio), new_folio);
+ VM_WARN_ON_FOLIO(!folio_is_zone_device(new_folio), new_folio);
+ }
+}
+EXPORT_SYMBOL_GPL(free_zone_device_folio_prepare);
+
void free_zone_device_folio(struct folio *folio)
{
struct dev_pagemap *pgmap = folio->pgmap;
@@ -454,6 +508,7 @@ void free_zone_device_folio(struct folio *folio)
case MEMORY_DEVICE_COHERENT:
if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->folio_free))
break;
+ free_zone_device_folio_prepare(folio);
pgmap->ops->folio_free(folio, order);
percpu_ref_put_many(&folio->pgmap->ref, nr);
break;
--
2.43.0
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