Messages in this thread | | | Date | Wed, 5 May 2021 15:36:47 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH 11/15] KVM: VMX: Disable loading of TSX_CTRL MSR the more conventional way |
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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.
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