On Mon, 17 May 2021 22:07:47 +0200 Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> wrote: > Previously, when a protected VM was rebooted or when it was shut down, > its memory was made unprotected, and then the protected VM itself was > destroyed. Looping over the whole address space can take some time, > considering the overhead of the various Ultravisor Calls (UVCs). This > means that a reboot or a shutdown would take a potentially long amount > of time, depending on the amount of used memory. > > This patchseries implements a deferred destroy mechanism for protected > guests. When a protected guest is destroyed, its memory is cleared in > background, allowing the guest to restart or terminate significantly > faster than before. > > There are 2 possibilities when a protected VM is torn down: > * it still has an address space associated (reboot case) > * it does not have an address space anymore (shutdown case) > > For the reboot case, the reference count of the mm is increased, and > then a background thread is started to clean up. Once the thread went > through the whole address space, the protected VM is actually > destroyed. > > For the shutdown case, a list of pages to be destroyed is formed when > the mm is torn down. Instead of just unmapping the pages when the > address space is being torn down, they are also set aside. Later when > KVM cleans up the VM, a thread is started to clean up the pages from > the list. Just to make sure, 'clean up' includes doing uv calls? > > This means that the same address space can have memory belonging to > more than one protected guest, although only one will be running, the > others will in fact not even have any CPUs. Are those set-aside-but-not-yet-cleaned-up pages still possibly accessible in any way? I would assume that they only belong to the 'zombie' guests, and any new or rebooted guest is a new entity that needs to get new pages? Can too many not-yet-cleaned-up pages lead to a (temporary) memory exhaustion?
