On Fri, Apr 1, 2022 at 11:02 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > On Fri, Apr 01, 2022, Marc Orr wrote: > > On Thu, Mar 31, 2022 at 12:01 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > Yep, that's a big reason why I view purging the existing SEV memory management as > > > a long term goal. The other being that userspace obviously needs to be updated to > > > support UPM[*]. I suspect the only feasible way to enable this for SEV/SEV-ES > > > would be to restrict it to new VM types that have a disclaimer regarding additional > > > requirements. > > > > > > [*] I believe Peter coined the UPM acronym for "Unmapping guest Private Memory". We've > > > been using it iternally for discussion and it rolls off the tongue a lot easier than > > > the full phrase, and is much more precise/descriptive than just "private fd". > > > > Can we really "purge the existing SEV memory management"? This seems > > like a non-starter because it violates userspace API (i.e., the > > ability for the userspace VMM to run a guest without > > KVM_FEATURE_HC_MAP_GPA_RANGE). Or maybe I'm not quite following what > > you mean by purge. > > I really do mean purge, but I also really do mean "long term", as in 5+ years > (probably 10+ if I'm being realistic). > > Removing support is completely ok, as is changing the uABI, the rule is that we > can't break userspace. If all users are migrated to private-fd, e.g. by carrots > and/or sticks such as putting the code into maintenance-only mode, then at some > point in the future there will be no users left to break and we can drop the > current code and make use of private-fd mandatory for SEV/SEV-ES guests. Ah, it makes sense now. Thanks! > > Assuming that UPM-based lazy pinning comes together via a new VM type > > that only supports new images based on a minimum kernel version with > > KVM_FEATURE_HC_MAP_GPA_RANGE, then I think this would like as follows: > > > > 1. Userspace VMM: Check SEV VM type. If type is legacy SEV type then > > do upfront pinning. Else, skip up front pinning. > > Yep, if by legacy "SEV type" you mean "SEV/SEV-ES guest that isn't required to > use MAP_GPA_RANGE", which I'm pretty sure you do based on #3. Yeah, that's exactly what I meant. > > 2. KVM: I'm not sure anything special needs to happen here. For the > > legacy VM types, it can be configured to use legacy memslots, > > presumably the same as non-CVMs will be configured. For the new VM > > type, it should be configured to use UPM. > > Correct, for now, KVM does nothing different for SEV/SEV-ES guests. > > > 3. Control plane (thing creating VMs): Responsible for not allowing > > legacy SEV images (i.e., images without KVM_FEATURE_HC_MAP_GPA_RANGE) > > with the new SEV VM types that use UPM and have support for demand > > pinning. > > > > Sean: Did I get this right? > > Yep. Thank you for verifying.
