On Thu, Mar 14, 2024 at 03:56:27PM -0700, Sean Christopherson wrote: > On Thu, Mar 14, 2024, Michael Roth wrote: > > On Wed, Mar 13, 2024 at 09:49:52PM -0500, Michael Roth wrote: > > > I've been trying to get SNP running on top of these patches and hit and > > > issue with these due to fpstate_set_confidential() being done during > > > svm_vcpu_create(), so when QEMU tries to sync FPU state prior to calling > > > SNP_LAUNCH_FINISH it errors out. I think the same would happen with > > > SEV-ES as well. > > > > > > Maybe fpstate_set_confidential() should be relocated to SEV_LAUNCH_FINISH > > > site as part of these patches? > > > > Talked to Tom a bit about this and that might not make much sense unless > > we actually want to add some code to sync that FPU state into the VMSA > > prior to encryption/measurement. Otherwise, it might as well be set to > > confidential as soon as vCPU is created. > > > > And if userspace wants to write FPU register state that will not actually > > become part of the guest state, it probably does make sense to return an > > error for new VM types and leave it to userspace to deal with > > special-casing that vs. the other ioctls like SET_REGS/SREGS/etc. > > Won't regs and sregs suffer the same fate? That might not matter _today_ for > "real" VMs, but it would be a blocking issue for selftests, which need to stuff > state to jumpstart vCPUs. SET_REGS/SREGS and the others only throw an error when vcpu->arch.guest_state_protected gets set, which doesn't happen until sev_launch_update_vmsa(). So in those cases userspace is still able to sync additional/non-reset state prior initial launch. It's just XSAVE/XSAVE2 that are a bit more restrictive because they check fpstate_is_confidential() instead, which gets set during vCPU creation. Somewhat related, but just noticed that KVM_SET_FPU also relies on fpstate_is_confidential() but still silently returns 0 with this series. Seems like it should be handled the same way as XSAVE/XSAVE2, whatever we end up doing. -Mike > > And maybe someday real VMs will catch up to the times and stop starting at the > RESET vector... >
