On Mon, Jan 16, 2023, Nikunj A. Dadhania wrote: > On 13/01/23 21:47, Sean Christopherson wrote: > > It's perfectly legal for userspace to create the private memslot in response > > to a guest request. > > Sean, did not understand this part, how could a memslot be created on a guest request? KVM_HC_MAP_GPA_RANGE gets routed to host userspace, at that point userspace can take any action it wants to satisfy the guest request. E.g. a userspace+guest setup could define memory as shared by default, and only create KVM_MEM_PRIVATE memslots for memory that the guest explicitly requests to be mapped private. I don't anticipate any real world use cases actually doing something like that, but I also don't see any value in going out of our way to disallow it. Normally I like to be conservative when it comes to KVM's uAPI, e.g. allow the minimum needed to support known use cases, but restricting KVM_HC_MAP_GPA_RANGE doesn't actually achieve anything and just makes things more complex for KVM. E.g. the behavior is non-deterministic from KVM's perspective if a userspace memslots update is in-progress.
