On Tue, May 25, 2021, Paolo Bonzini wrote: > On 25/05/21 17:58, Sean Christopherson wrote: > > > The right place for the hw multiplier > > > field to be updated is inside set_tsc_khz() in common code when the ratio > > > changes. > > Sort of, the problem is that you have two VMCS's to update. If properly > fixed, the cache is useful to fix the issue with KVM_SET_TSC_KHZ needing to > update both of them. For that to work, you'd have to move the cache to > struct loaded_vmcs. vmcs01 and vmcs02 will get updated at enter/exit, if there's no caching then it all Just Works. > So you can: > > 1) move the cached tsc_ratio to struct loaded_vmcs > > 2) add a function in common code (update_tsc_parameters or something like > that) to update both the offset and the ratio depending on is_guest_mode() > > 3) call that function from nested vmentry/vmexit > > And at that point the cache will do its job and figure out whether a vmwrite > is needed, on both vmentry and vmexit. > > I actually like the idea of storing the expected value in kvm_vcpu and the > current value in loaded_vmcs. We might use it for other things such as > reload_vmcs01_apic_access_page perhaps. I'm not necessarily opposed to aggressively shadowing the VMCS, but if we go that route then it should be a standalone series that implements a framework that can be easily extended to arbitrary fields. Adding fields to loaded_vmcs one at a time will be tedious and error prone. E.g. what makes TSC_MULTIPLIER more special than TSC_OFFSET, GUEST_IA32_PAT, GUEST_IA32_DEBUGCTL, GUEST_BNDCFGS, and other number of fields that are likely to persist for a given vmcs02? The current caching logic is just plain ugly and should not exist.
