On Tue, May 4, 2021 at 1:56 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > On 04/05/21 22:33, Sean Christopherson wrote: > > On Tue, May 04, 2021, Paolo Bonzini wrote: > >> On 04/05/21 19:09, Sean Christopherson wrote: > >>> On Sat, May 01, 2021, Paolo Bonzini wrote: > >>>> - make it completely independent from migration, i.e. it's just a facet of > >>>> MSR_KVM_PAGE_ENC_STATUS saying whether the bitmap is up-to-date. It would > >>>> use CPUID bit as the encryption status bitmap and have no code at all in KVM > >>>> (userspace needs to set up the filter and implement everything). > >>> > >>> If the bit is purely a "page encryption status is up-to-date", what about > >>> overloading KVM_HC_PAGE_ENC_STATUS to handle that status update as well? That > >>> would eliminate my biggest complaint about having what is effectively a single > >>> paravirt feature split into two separate, but intertwined chunks of ABI. > >> > >> It's true that they are intertwined, but I dislike not having a way to read > >> the current state. > > > > From the guest? > > Yes, host userspace obviously doesn't need one since it's implemented > through an MSR filter. It may not be really necessary to read it, but > it's a bit jarring compared to how the rest of the PV APIs uses MSRs. > > Also from a debugging/crashdump point of view the VMM may have an > established way to read an MSR from a vCPU, but it won't work if you > come up with a new way to set the state. Agreed on the preference for an MSR. I particularly appreciate that it reduces the kernel footprint for these changes. Steve
