On Wed, Jul 3, 2024 at 10:35 AM Nikita Kalyazin <kalyazin@xxxxxxxxxx> wrote: > > Hi David, > > On 11/03/2024 16:20, David Matlack wrote: > > On Sun, Mar 10, 2024 at 9:46 PM Oliver Upton <oliver.upton@xxxxxxxxx> wrote: > >>>> > >>>> 2. What is your best guess as to when KVM userfault patches will be available, > >>>> even if only in RFC form? > >>> > >>> We're aiming for the end of April for RFC with KVM/ARM support. > >> > >> Just to make sure everyone is read in on what this entails -- is this > >> the implementation that only worries about vCPUs touching non-present > >> memory, leaving the question of other UAPIs that consume guest memory > >> (e.g. GIC/ITS table save/restore) up for further discussion? > > > > Yes. The initial version will only support returning to userspace on > > invalid vCPU accesses with KVM_EXIT_MEMORY_FAULT. Non-vCPU accesses to > > invalid pages (e.g. GIC/ITS table save/restore) will trigger an error > > return from __gfn_to_hva_many() (which will cause the corresponding > > ioctl to fail). It will be userspace's responsibility to clear the > > invalid attribute before invoking those ioctls. > > > > For x86 we may need an blocking kernel-to-userspace notification > > mechanism for code paths in the emulator, but we'd like to investigate > > and discuss if there are any other cleaner alternatives before going > > too far down that route. > > I wasn't able to locate any follow-ups on the LKML about this topic. > May I know if you are still working on or planning to work on this? Yes, James Houghton at Google has been working on this. We decided to build a more complete RFC (with x86 and ARM) support, so that reviewers can get an idea of the full scope of the feature, so it has taken a bit longer than originally planned. But the RFC is code complete now. I think James is planning to send the patches next week.
