[HMM v15 03/16] mm/ZONE_DEVICE/devmem_pages_remove: allow early removal of device memory

["Jérôme Glisse" <jglisse@redhat.com>]

Some device driver manage multiple physical devices memory from a single
fake device driver. In that case the fake device might outlive the real
device and ZONE_DEVICE and its resource allocated for a real device would
waste resources in the meantime.

This patch allow early removal of ZONE_DEVICE and associated resource,
before device driver is tear down.

Signed-off-by: JA(C)rA'me Glisse <jglisse@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 include/linux/memremap.h |  7 +++++++
 kernel/memremap.c        | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index f7e0609..32314d2 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -53,6 +53,7 @@ struct dev_pagemap {
 void *devm_memremap_pages(struct device *dev, struct resource *res,
 		struct percpu_ref *ref, struct vmem_altmap *altmap);
 struct dev_pagemap *find_dev_pagemap(resource_size_t phys);
+int devm_memremap_pages_remove(struct device *dev, struct dev_pagemap *pgmap);
 
 static inline bool dev_page_allow_migrate(const struct page *page)
 {
@@ -78,6 +79,12 @@ static inline struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
 	return NULL;
 }
 
+static inline int devm_memremap_pages_remove(struct device *dev,
+					     struct dev_pagemap *pgmap)
+{
+	return -EINVAL;
+}
+
 static inline bool dev_page_allow_migrate(const struct page *page)
 {
 	return false;
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 07665eb..250ef25 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -387,6 +387,20 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
 }
 EXPORT_SYMBOL(devm_memremap_pages);
 
+static int devm_page_map_match(struct device *dev, void *data, void *match_data)
+{
+	struct page_map *page_map = data;
+
+	return &page_map->pgmap == match_data;
+}
+
+int devm_memremap_pages_remove(struct device *dev, struct dev_pagemap *pgmap)
+{
+	return devres_release(dev, &devm_memremap_pages_release,
+			      &devm_page_map_match, pgmap);
+}
+EXPORT_SYMBOL(devm_memremap_pages_remove);
+
 unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
 {
 	/* number of pfns from base where pfn_to_page() is valid */
-- 
2.4.3

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