Hello there, I'm trying to debug several, probably related issues to your hv_balloon kernel module. All tests are done on Win11 21H2 (22000.675) pro, on a Ryzen 3950x with active AMD-V, and 64GB of memory. An updated Ubuntu Server 20.04 Guest is used for comparison. It's currently running kernel 5.13.0-1023-azure, configured with 1GB memory to start, and active ballooning between 512MB and 32GB of memory. Memory hot-plugging and -unplugging works. Issues showed up when I set up a Kali Linux Guest. I missed the memory configuration before booting up the instance, so it started with 1GB of memory, and ballooning active between 512MB and several TB of memory. Hyper-V started to allocate more and more memory to this guest since the reported memory requirements also increased. The guest kernel didn't see any of that allocated memory, as far as I can tell. This is clearly reproduceable on at least 2 Hyper-V hosts, with current live images of Debian (Bullseye) and Kali Linux, but not with Ubuntu 20.04 or 22.04. (Get the Kali live image, create a new guest (version 10), turn off secure boot and boot from that image. It takes 3-5 minutes until the issue is visible in the hyper-v console.) After running more tests with different memory settings for ballooning, I am pretty sure: - Hyper-V respects the maximum setting for the memory balloon. Although it doesn't care if there's enough memory. - Guests can't use/see more memory than they had while booting up. - Guests can unplug memory. - Guests can hotplug previously unplugged memory up to their starting amount. - The reported values seem to be off: After compiling a kernel on Kali (and cooling down), the guest kernel shows a total of 3207MB memory, with 294MB used, 137MB free, 2775MB buffers/caches and 2611MB available. Hyper-V reports 4905MB required and 5840MB allocated. - As of kernel 5.17.11, the issue is not solved. To sum up: I could use memory ballooning if I set the initial memory size to the maximum size and wait until it got freed up. There are several reports out there about what looks like a memory leak, without a solution. I'm currently comparing the kernel built by canonical with the kali kernel, but as I am not really a developer, I'm not sure if I could even find the difference if there is one. So, I'm calling (and hoping) for help, and offering any support when it comes to testing. I can apply patches, build kernel packages and read logs if that helps. Thx-a-lot! Flo