On Wed, Nov 8, 2023 at 12:33 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > On 11/8/23 17:56, David Matlack wrote: > > Thanks for the longer explanation. Yes kvm_read_guest() eventually calls > > __copy_from_user() which will trigger a page fault and UserfaultFD will > > notify userspace and wait for the page to become present. In the > > KVM-specific proposal I outlined, calling kvm_read_guest() will > > ultimately result in a check of the VM's present bitmap and KVM will > > nnotify userspace and wait for the page to become present if it's not, > > before calling __copy_from_user(). So I don't expect a KVM-specific > > solution to have any increased maintenance burden for VGIC (or any other > > widgets). > > It does mean however that we need a cross-thread notification mechanism, > instead of just relying on KVM_EXIT_MEMORY_FAULT (or another KVM_EXIT_*). Yes. Any time KVM directly accesses guest memory (e.g. kvm_read/write_guest()), it would use a blocking notification mechanism (part (d) in the proposal). Google uses a netlink socket for this, but a custom file descriptor would be more reliable.
