[PATCH v1 07/15] memory-device: Support memory devices that statically consume multiple memslots

[David Hildenbrand <david@redhat.com>]

We want to support memory devices that have a memory region container as
device memory region where they statically map multiple RAM memory
regions.

We already have one device that uses a container as device memory region:
NVDIMMs. However, a NVDIMM always ends up consuming exactly one memslot.

Let's add support for that by asking the memory device via a new
callback how many memslots it consumes.

While at it in memory_device_check_addable(), perform the region size
check first and don't check separately for KVM and vhost, both things will
come in handy later.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/mem/memory-device.c         | 46 +++++++++++++++++++++++-----------
 include/hw/mem/memory-device.h | 18 +++++++++++++
 2 files changed, 49 insertions(+), 15 deletions(-)

diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
index 2f19183a25..a9dcc0c4ef 100644
--- a/hw/mem/memory-device.c
+++ b/hw/mem/memory-device.c
@@ -82,6 +82,12 @@ static unsigned int get_max_memslots(void)
     return MIN(vhost_get_max_memslots(), kvm_get_max_memslots());
 }
 
+/* Overall number of free memslots */
+static unsigned int get_free_memslots(void)
+{
+    return MIN(vhost_get_free_memslots(), kvm_get_free_memslots());
+}
+
 /*
  * The memslot soft limit for memory devices. The soft limit might change at
  * runtime in corner cases (that should certainly be avoided), for example, when
@@ -126,21 +132,23 @@ void memory_devices_notify_vhost_device_added(void)
     memory_devices_check_memslot_soft_limit(ms);
 }
 
-static void memory_device_check_addable(MachineState *ms, MemoryRegion *mr,
-                                        Error **errp)
+static unsigned int memory_device_get_memslots(MemoryDeviceState *md)
 {
-    const uint64_t used_region_size = ms->device_memory->used_region_size;
-    const uint64_t size = memory_region_size(mr);
+    const MemoryDeviceClass *mdc = MEMORY_DEVICE_GET_CLASS(md);
 
-    /* we will need a new memory slot for kvm and vhost */
-    if (!kvm_get_free_memslots()) {
-        error_setg(errp, "hypervisor has no free memory slots left");
-        return;
-    }
-    if (!vhost_get_free_memslots()) {
-        error_setg(errp, "a used vhost backend has no free memory slots left");
-        return;
+    if (mdc->get_memslots) {
+        return mdc->get_memslots(md);
     }
+    return 1;
+}
+
+static void memory_device_check_addable(MachineState *ms, MemoryDeviceState *md,
+                                        MemoryRegion *mr, Error **errp)
+{
+    const uint64_t used_region_size = ms->device_memory->used_region_size;
+    const unsigned int available_memslots = get_free_memslots();
+    const uint64_t size = memory_region_size(mr);
+    unsigned int required_memslots;
 
     /* will we exceed the total amount of memory specified */
     if (used_region_size + size < used_region_size ||
@@ -151,6 +159,14 @@ static void memory_device_check_addable(MachineState *ms, MemoryRegion *mr,
         return;
     }
 
+    /* ... are there still sufficient memslots available? */
+    required_memslots = memory_device_get_memslots(md);
+    if (available_memslots < required_memslots) {
+        error_setg(errp, "Insufficient memory slots for memory device"
+                   "available. Available: %u, Required: %u",
+                   available_memslots, required_memslots);
+        return;
+    }
 }
 
 static uint64_t memory_device_get_free_addr(MachineState *ms,
@@ -307,7 +323,7 @@ void memory_device_pre_plug(MemoryDeviceState *md, MachineState *ms,
         goto out;
     }
 
-    memory_device_check_addable(ms, mr, &local_err);
+    memory_device_check_addable(ms, md, mr, &local_err);
     if (local_err) {
         goto out;
     }
@@ -349,7 +365,7 @@ void memory_device_plug(MemoryDeviceState *md, MachineState *ms)
     g_assert(ms->device_memory);
 
     ms->device_memory->used_region_size += memory_region_size(mr);
-    ms->device_memory->required_memslots++;
+    ms->device_memory->required_memslots += memory_device_get_memslots(md);
     memory_devices_check_memslot_soft_limit(ms);
     memory_region_add_subregion(&ms->device_memory->mr,
                                 addr - ms->device_memory->base, mr);
@@ -370,7 +386,7 @@ void memory_device_unplug(MemoryDeviceState *md, MachineState *ms)
 
     memory_region_del_subregion(&ms->device_memory->mr, mr);
     ms->device_memory->used_region_size -= memory_region_size(mr);
-    ms->device_memory->required_memslots--;
+    ms->device_memory->required_memslots -= memory_device_get_memslots(md);
     trace_memory_device_unplug(DEVICE(md)->id ? DEVICE(md)->id : "",
                                mdc->get_addr(md));
 }
diff --git a/include/hw/mem/memory-device.h b/include/hw/mem/memory-device.h
index 813c3b9da6..755f6304c6 100644
--- a/include/hw/mem/memory-device.h
+++ b/include/hw/mem/memory-device.h
@@ -42,6 +42,11 @@ typedef struct MemoryDeviceState MemoryDeviceState;
  * successive memory regions are used, a covering memory region has to
  * be provided. Scattered memory regions are not supported for single
  * devices.
+ *
+ * The device memory region returned via @get_memory_region may either be a
+ * single RAM/ROM memory region or a memory region container with subregions
+ * that are RAM/ROM memory regions or aliases to RAM/ROM memory regions. Other
+ * memory regions or subregions are not supported.
  */
 struct MemoryDeviceClass {
     /* private */
@@ -89,6 +94,19 @@ struct MemoryDeviceClass {
      */
     MemoryRegion *(*get_memory_region)(MemoryDeviceState *md, Error **errp);
 
+    /*
+     * Optional for memory devices that consume only a single memslot,
+     * required for all other memory devices: Return the number of memslots
+     * (distinct RAM memory regions in the device memory region) that are
+     * required by the device.
+     *
+     * If this function is not implemented, the assumption is "1".
+     *
+     * Called when (un)plugging the memory device, to check if the requirements
+     * can be satisfied, and to do proper accounting.
+     */
+    unsigned int (*get_memslots)(MemoryDeviceState *md);
+
     /*
      * Optional: Return the desired minimum alignment of the device in guest
      * physical address space. The final alignment is computed based on this
-- 
2.40.1