From 052f38fa96e19dcd4d2a1545227b181b4c761ef9 Mon Sep 17 00:00:00 2001
From: Sebastien Boeuf <sebastien.boeuf@intel.com>
Date: Thu, 10 Feb 2022 14:47:33 +0100
Subject: [PATCH] vmm: Enable guest to report free pages through virtio-balloon

Adding a new parameter free_page_reporting=on|off to the balloon device
so that we can enable the corresponding feature from virtio-balloon.

Running a VM with a balloon device where this feature is enabled allows
the guest to report pages that are free from guest's perspective. This
information is used by the VMM to release the corresponding pages on the
host.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
---
 virtio-devices/src/balloon.rs             |  1 +
 vmm/src/api/openapi/cloud-hypervisor.yaml |  6 +++++-
 vmm/src/config.rs                         | 14 +++++++++++++-
 vmm/src/device_manager.rs                 |  1 +
 4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/virtio-devices/src/balloon.rs b/virtio-devices/src/balloon.rs
index d03be1cc8..ab85ab363 100644
--- a/virtio-devices/src/balloon.rs
+++ b/virtio-devices/src/balloon.rs
@@ -392,6 +392,7 @@ impl Balloon {
         id: String,
         size: u64,
         deflate_on_oom: bool,
+        _free_page_reporting: bool,
         seccomp_action: SeccompAction,
         exit_evt: EventFd,
     ) -> io::Result<Self> {
diff --git a/vmm/src/api/openapi/cloud-hypervisor.yaml b/vmm/src/api/openapi/cloud-hypervisor.yaml
index 77706e80a..6bb8e989b 100644
--- a/vmm/src/api/openapi/cloud-hypervisor.yaml
+++ b/vmm/src/api/openapi/cloud-hypervisor.yaml
@@ -800,7 +800,11 @@ components:
         deflate_on_oom:
           type: boolean
           default: false
-          description: Whether the balloon should deflate when the guest is under memory pressure.
+          description: Deflate balloon when the guest is under memory pressure.
+        free_page_reporting:
+          type: boolean
+          default: false
+          description: Enable guest to report free pages.
 
     FsConfig:
       required:
diff --git a/vmm/src/config.rs b/vmm/src/config.rs
index 8bd8e9747..6616f2bd7 100644
--- a/vmm/src/config.rs
+++ b/vmm/src/config.rs
@@ -1383,16 +1383,21 @@ pub struct BalloonConfig {
     /// Option to deflate the balloon in case the guest is out of memory.
     #[serde(default)]
     pub deflate_on_oom: bool,
+    /// Option to enable free page reporting from the guest.
+    #[serde(default)]
+    pub free_page_reporting: bool,
 }
 
 impl BalloonConfig {
     pub const SYNTAX: &'static str =
-        "Balloon parameters \"size=<balloon_size>,deflate_on_oom=on|off\"";
+        "Balloon parameters \"size=<balloon_size>,deflate_on_oom=on|off,\
+        free_page_reporting=on|off\"";
 
     pub fn parse(balloon: &str) -> Result<Self> {
         let mut parser = OptionParser::new();
         parser.add("size");
         parser.add("deflate_on_oom");
+        parser.add("free_page_reporting");
         parser.parse(balloon).map_err(Error::ParseBalloon)?;
 
         let size = parser
@@ -1407,9 +1412,16 @@ impl BalloonConfig {
             .unwrap_or(Toggle(false))
             .0;
 
+        let free_page_reporting = parser
+            .convert::<Toggle>("free_page_reporting")
+            .map_err(Error::ParseBalloon)?
+            .unwrap_or(Toggle(false))
+            .0;
+
         Ok(BalloonConfig {
             size,
             deflate_on_oom,
+            free_page_reporting,
         })
     }
 }
diff --git a/vmm/src/device_manager.rs b/vmm/src/device_manager.rs
index a52e324a5..2c6eefec7 100644
--- a/vmm/src/device_manager.rs
+++ b/vmm/src/device_manager.rs
@@ -2786,6 +2786,7 @@ impl DeviceManager {
                     id.clone(),
                     balloon_config.size,
                     balloon_config.deflate_on_oom,
+                    balloon_config.free_page_reporting,
                     self.seccomp_action.clone(),
                     self.exit_evt
                         .try_clone()