Subject: [RFC PATCH v2 02/21] mm/memory_hotplug: add {add|release}_memory_pages

From: Jonathan Lemon <[email-masked]>
Date: Mon, 27 Jul 2020 15:44:25 -0700

These calls allows creation of system pages at a specific physical
address, which is useful for creating dummy backing pages which
correspond to unaddressable external memory at specific locations.

__add_memory_pages() adds the requested page range to /proc/iomem and
verifies that there are no overlaps.  Once this succeeds, then the page
section is initialized, which may overlap with a prior request, since
section sizes are large, so ignore the latter overlap.

Signed-off-by: Jonathan Lemon <[email-masked]>
---
 include/linux/memory_hotplug.h |  4 +++
 mm/memory_hotplug.c            | 65 ++++++++++++++++++++++++++++++++--
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 375515803cd8..05e012e1a203 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -138,6 +138,10 @@ extern void __remove_pages(unsigned long start_pfn, unsigned long nr_pages,
 extern int __add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
 		       struct mhp_params *params);
 
+struct resource *add_memory_pages(int nid, u64 start, u64 size,
+                                  struct mhp_params *params);
+void release_memory_pages(struct resource *res);
+
 #ifndef CONFIG_ARCH_HAS_ADD_PAGES
 static inline int add_pages(int nid, unsigned long start_pfn,
 		unsigned long nr_pages, struct mhp_params *params)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index da374cd3d45b..c1a923189869 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -125,8 +125,8 @@ static struct resource *register_memory_resource(u64 start, u64 size,
 			       resource_name, flags);
 
 	if (!res) {
-		pr_debug("Unable to reserve System RAM region: %016llx->%016llx\n",
-				start, start + size);
+		pr_debug("Unable to reserve %s region: %016llx->%016llx\n",
+				resource_name, start, start + size);
 		return ERR_PTR(-EEXIST);
 	}
 	return res;
@@ -1118,6 +1118,67 @@ int add_memory(int nid, u64 start, u64 size)
 }
 EXPORT_SYMBOL_GPL(add_memory);
 
+static int __ref add_memory_section(int nid, struct resource *res,
+				    struct mhp_params *params)
+{
+	u64 start, end, section_size;
+	int ret;
+
+	/* must align start/end with memory block size */
+	end = res->start + resource_size(res);
+	section_size = memory_block_size_bytes();
+	start = round_down(res->start, section_size);
+	end = round_up(end, section_size);
+
+	mem_hotplug_begin();
+	ret = __add_pages(nid,
+		PHYS_PFN(start), PHYS_PFN(end - start), params);
+	mem_hotplug_done();
+
+	return ret;
+}
+
+/* requires device_hotplug_lock, see add_memory_resource() */
+static struct resource * __ref __add_memory_pages(int nid, u64 start, u64 size,
+				    struct mhp_params *params)
+{
+	struct resource *res;
+	int ret;
+
+	res = register_memory_resource(start, size, "Private RAM");
+	if (IS_ERR(res))
+		return res;
+
+	ret = add_memory_section(nid, res, params);
+	if (ret < 0 && ret != -EEXIST) {
+		release_memory_resource(res);
+		return ERR_PTR(ret);
+	}
+
+	return res;
+}
+
+struct resource *add_memory_pages(int nid, u64 start, u64 size,
+				  struct mhp_params *params)
+{
+	struct resource *res;
+
+	lock_device_hotplug();
+	res = __add_memory_pages(nid, start, size, params);
+	unlock_device_hotplug();
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(add_memory_pages);
+
+void release_memory_pages(struct resource *res)
+{
+	lock_device_hotplug();
+	release_memory_resource(res);
+	unlock_device_hotplug();
+}
+EXPORT_SYMBOL_GPL(release_memory_pages);
+
 /*
  * Add special, driver-managed memory to the system as system RAM. Such
  * memory is not exposed via the raw firmware-provided memmap as system
-- 
2.24.1