[PATCH RCFv2 4/7] mm/memory_hotplug: allow to control onlining/offlining of memory by a driver

[David Hildenbrand]

Some devices (esp. paravirtualized) might want to control
- when to online/offline a memory block
- how to online memory (MOVABLE/NORMAL)
- in which granularity to online/offline memory

So let's add a new flag "driver_managed" and disallow to change the
state by user space. Device onlining/offlining will still work, however
the memory will not be actually onlined/offlined. That has to be handled
by the device driver that owns the memory.

Please note that we have to create user visible memory blocks after all
since this is required to trigger the right udevs events in order to
reload kexec/kdump. Also, it allows to see what is going on in the
system (e.g. which memory blocks are still around).

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Reza Arbab <arbab@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 drivers/base/memory.c          | 22 ++++++++++++++--------
 drivers/xen/balloon.c          |  2 +-
 include/linux/memory.h         |  1 +
 include/linux/memory_hotplug.h |  4 +++-
 mm/memory_hotplug.c            | 34 ++++++++++++++++++++++++++++++++--
 5 files changed, 51 insertions(+), 12 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index bffe8616bd55..3b8616551561 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -231,27 +231,28 @@ static bool pages_correctly_probed(unsigned long start_pfn)
  * Must already be protected by mem_hotplug_begin().
  */
 static int
-memory_block_action(unsigned long phys_index, unsigned long action, int online_type)
+memory_block_action(struct memory_block *mem, unsigned long action)
 {
-	unsigned long start_pfn;
+	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
-	int ret;
+	int ret = 0;
 
-	start_pfn = section_nr_to_pfn(phys_index);
+	if (mem->driver_managed)
+		return 0;
 
 	switch (action) {
 	case MEM_ONLINE:
 		if (!pages_correctly_probed(start_pfn))
 			return -EBUSY;
 
-		ret = online_pages(start_pfn, nr_pages, online_type);
+		ret = online_pages(start_pfn, nr_pages, mem->online_type);
 		break;
 	case MEM_OFFLINE:
 		ret = offline_pages(start_pfn, nr_pages);
 		break;
 	default:
 		WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
-		     "%ld\n", __func__, phys_index, action, action);
+		     "%ld\n", __func__, mem->start_section_nr, action, action);
 		ret = -EINVAL;
 	}
 
@@ -269,8 +270,7 @@ static int memory_block_change_state(struct memory_block *mem,
 	if (to_state == MEM_OFFLINE)
 		mem->state = MEM_GOING_OFFLINE;
 
-	ret = memory_block_action(mem->start_section_nr, to_state,
-				mem->online_type);
+	ret = memory_block_action(mem, to_state);
 
 	mem->state = ret ? from_state_req : to_state;
 
@@ -350,6 +350,11 @@ store_mem_state(struct device *dev,
 	 */
 	mem_hotplug_begin();
 
+	if (mem->driver_managed) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	switch (online_type) {
 	case MMOP_ONLINE_KERNEL:
 	case MMOP_ONLINE_MOVABLE:
@@ -364,6 +369,7 @@ store_mem_state(struct device *dev,
 		ret = -EINVAL; /* should never happen */
 	}
 
+out:
 	mem_hotplug_done();
 err:
 	unlock_device_hotplug();
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 065f0b607373..89981d573c06 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -401,7 +401,7 @@ static enum bp_state reserve_additional_memory(void)
 	 * callers drop the mutex before trying again.
 	 */
 	mutex_unlock(&balloon_mutex);
-	rc = add_memory_resource(nid, resource, memhp_auto_online);
+	rc = add_memory_resource(nid, resource, memhp_auto_online, false);
 	mutex_lock(&balloon_mutex);
 
 	if (rc) {
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 9f8cd856ca1e..018c5e5ecde1 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -29,6 +29,7 @@ struct memory_block {
 	unsigned long state;		/* serialized by the dev->lock */
 	int section_count;		/* serialized by mem_sysfs_mutex */
 	int online_type;		/* for passing data to online routine */
+	bool driver_managed;		/* driver handles online/offline */
 	int phys_device;		/* to which fru does this belong? */
 	void *hw;			/* optional pointer to fw/hw data */
 	int (*phys_callback)(struct memory_block *);
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index d71829d54360..497e28f5b000 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -326,7 +326,9 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
 extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
 		void *arg, int (*func)(struct memory_block *, void *));
 extern int add_memory(int nid, u64 start, u64 size);
-extern int add_memory_resource(int nid, struct resource *resource, bool online);
+extern int add_memory_driver_managed(int nid, u64 start, u64 size);
+extern int add_memory_resource(int nid, struct resource *resource, bool online,
+			       bool driver_managed);
 extern int arch_add_memory(int nid, u64 start, u64 size,
 		struct vmem_altmap *altmap, bool want_memblock);
 extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c971295a1100..4c7e0efff079 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1109,8 +1109,15 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 	return device_online(&mem->dev);
 }
 
+static int mark_memory_block_driver_managed(struct memory_block *mem, void *arg)
+{
+	mem->driver_managed = true;
+	return 0;
+}
+
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-int __ref add_memory_resource(int nid, struct resource *res, bool online)
+int __ref add_memory_resource(int nid, struct resource *res, bool online,
+			      bool driver_managed)
 {
 	u64 start, size;
 	pg_data_t *pgdat = NULL;
@@ -1118,6 +1125,9 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	bool new_node;
 	int ret;
 
+	if (online && driver_managed)
+		return -EINVAL;
+
 	start = res->start;
 	size = resource_size(res);
 
@@ -1189,6 +1199,9 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	if (online)
 		walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1),
 				  NULL, online_memory_block);
+	else if (driver_managed)
+		walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1),
+				  NULL, mark_memory_block_driver_managed);
 
 	goto out;
 
@@ -1213,13 +1226,30 @@ int __ref add_memory(int nid, u64 start, u64 size)
 	if (IS_ERR(res))
 		return PTR_ERR(res);
 
-	ret = add_memory_resource(nid, res, memhp_auto_online);
+	ret = add_memory_resource(nid, res, memhp_auto_online, false);
 	if (ret < 0)
 		release_memory_resource(res);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(add_memory);
 
+int __ref add_memory_driver_managed(int nid, u64 start, u64 size)
+{
+	struct resource *res;
+	int ret;
+
+	res = register_memory_resource(start, size);
+	if (IS_ERR(res))
+		return PTR_ERR(res);
+
+	ret = add_memory_resource(nid, res, false, true);
+	if (ret < 0)
+		release_memory_resource(res);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(add_memory_driver_managed);
+
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 /*
  * A free page on the buddy free lists (not the per-cpu lists) has PageBuddy
-- 
2.14.3