On Wed, May 05, 2021, Paolo Bonzini wrote: > On 04/05/21 19:17, Sean Christopherson wrote: > > Tag TSX_CTRL as not needing to be loaded when RTM isn't supported in the > > host. Crushing the write mask to '0' has the same effect, but requires > > more mental gymnastics to understand. > > This doesn't explain _why_ this is now possible. What about: > > Now that user return MSRs is always present in the list, we don't have User return MSRs aren't always present in the list; this series doesn't change that behavior at all. > the problem that the TSX_CTRL MSR needs a slot vmx->guest_uret_msrs even > if RTM is not supported in the host (and therefore there is nothing to > enable). Thus we can simply tag TSX_CTRL as not needing to be loaded > instead of crushing the write mask to '0'. Unless I'm missing something, it would have been possible to give TSX_CTRL a slot but not load it even before this refactoring, we just missed that approach when handling the TSX_CTRL without HLE/RTM case. Several other MSRs rely on this behavior, notably the SYSCALL MSRs, which are present in the list so that the guest can read/write the MSRs, but are loaded into hardware iff the guest has enabled SYSCALL. All that said, I certainly have no objection to writing a longer changelog.
