vmm: Add 'hotplug_size' to memory zones

In anticipation for resizing support of an individual memory zone,
this commit introduces a new option 'hotplug_size' to '--memory-zone'
parameter. This defines the amount of memory that can be added through
each specific memory zone.

Because memory zone resize is tied to virtio-mem, make sure the user
selects 'virtio-mem' hotplug method, otherwise return an error.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

docs/memory.md

@@ -112,8 +112,7 @@ _Example_
 
 Amount of memory that can be dynamically added to the VM.
 
-Value is an unsigned integer of 64 bits. A value of 0 simply means that no
+Value is an unsigned integer of 64 bits. A value of 0 is invalid.
-memory can be added to the VM.
 
 _Example_
 
@@ -149,11 +148,12 @@ struct MemoryZoneConfig {
     shared: bool,
     hugepages: bool,
     host_numa_node: Option<u32>,
+    hotplug_size: Option<u64>,
 }
 ```
 
 ```
---memory-zone <memory-zone>	User defined memory zone parameters "size=<guest_memory_region_size>,file=<backing_file>,shared=on|off,hugepages=on|off,host_numa_node=<node_id>,id=<zone_identifier>"
+--memory-zone <memory-zone>	User defined memory zone parameters "size=<guest_memory_region_size>,file=<backing_file>,shared=on|off,hugepages=on|off,host_numa_node=<node_id>,id=<zone_identifier>,hotplug_size=<hotpluggable_memory_size>"
 ```
 
 This parameter expects one or more occurences, allowing for a list of memory
@@ -288,6 +288,21 @@ _Example_
 --memory-zone id=mem0,size=1G,host_numa_node=0
 ```
 
+### `hotplug_size`
+
+Amount of memory that can be dynamically added to the memory zone. Since
+`virtio-mem` is the only way of resizing a memory zone, one must specify
+the `hotplug_method=virtio-mem` to the `--memory` parameter.
+
+Value is an unsigned integer of 64 bits. A value of 0 is invalid.
+
+_Example_
+
+```
+--memory size=0,hotplug_method=virtio-mem
+--memory-zone id=mem0,size=1G,hotplug_size=1G
+```
+
 ## NUMA settings
 
 `NumaConfig` or what is known as `--numa` from the CLI perspective has been

src/main.rs

@@ -121,7 +121,7 @@ fn create_app<'a, 'b>(
                     "User defined memory zone parameters \
                      \"size=<guest_memory_region_size>,file=<backing_file>,\
                      shared=on|off,hugepages=on|off,host_numa_node=<node_id>,\
-                     id=<zone_identifier>\"",
+                     id=<zone_identifier>,hotplug_size=<hotpluggable_memory_size>\"",
                 )
                 .takes_value(true)
                 .min_values(1)

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -477,6 +477,9 @@ components:
         host_numa_node:
           type: integer
           format: uint32
+        hotplug_size:
+          type: integer
+          format: int64
 
     MemoryConfig:
       required:

vmm/src/config.rs

@@ -379,6 +379,8 @@ pub struct MemoryZoneConfig {
     pub hugepages: bool,
     #[serde(default)]
     pub host_numa_node: Option<u32>,
+    #[serde(default)]
+    pub hotplug_size: Option<u64>,
 }
 
 #[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
@@ -460,7 +462,8 @@ impl MemoryConfig {
                     .add("file")
                     .add("shared")
                     .add("hugepages")
-                    .add("host_numa_node");
+                    .add("host_numa_node")
+                    .add("hotplug_size");
                 parser.parse(memory_zone).map_err(Error::ParseMemoryZone)?;
 
                 let id = parser.get("id").ok_or(Error::ParseMemoryZoneIdMissing)?;
@@ -483,6 +486,10 @@ impl MemoryConfig {
                 let host_numa_node = parser
                     .convert::<u32>("host_numa_node")
                     .map_err(Error::ParseMemoryZone)?;
+                let hotplug_size = parser
+                    .convert::<ByteSized>("hotplug_size")
+                    .map_err(Error::ParseMemoryZone)?
+                    .map(|v| v.0);
 
                 zones.push(MemoryZoneConfig {
                     id,
@@ -491,6 +498,7 @@ impl MemoryConfig {
                     shared,
                     hugepages,
                     host_numa_node,
+                    hotplug_size,
                 });
             }
             Some(zones)

vmm/src/memory_manager.rs

@@ -215,6 +215,9 @@ pub enum Error {
 
     /// Invalid size for resizing. Can be anything except 0.
     InvalidHotplugSize,
+
+    /// Invalid hotplug method associated with memory zones resizing capability.
+    InvalidHotplugMethodWithMemoryZones,
 }
 
 const ENABLE_FLAG: usize = 0;
@@ -442,6 +445,7 @@ impl MemoryManager {
                 shared: config.shared,
                 hugepages: config.hugepages,
                 host_numa_node: None,
+                hotplug_size: config.hotplug_size,
             }];
 
             (config.size, zones)
@@ -472,6 +476,11 @@ impl MemoryManager {
                     );
                     return Err(Error::InvalidSharedMemoryZoneWithHostNuma);
                 }
+
+                if zone.hotplug_size.is_some() && config.hotplug_method == HotplugMethod::Acpi {
+                    error!("Invalid to set ACPI hotplug method for memory zones");
+                    return Err(Error::InvalidHotplugMethodWithMemoryZones);
+                }
             }
 
             (total_ram_size, zones)