Messages in this thread | | | From | "Raslan, KarimAllah" <> | Subject | Re: [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest | Date | Thu, 12 Apr 2018 20:24:32 +0000 |
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On Thu, 2018-04-12 at 22:21 +0200, Paolo Bonzini wrote: > On 12/04/2018 19:21, Raslan, KarimAllah wrote: > > > > Now looking further at the code, it seems that everywhere in the code > > tsc_offset is treated as the L01 TSC_OFFSET. > > > > Like here: > > > > if (vmcs12->cpu_based_vm_exec_control & > > CPU_BASED_USE_TSC_OFFSETING) > > vmcs_write64(TSC_OFFSET, > > vcpu->arch.tsc_offset + vmcs12->tsc_offset); > > > > and here: > > > > vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset); > > > > and here: > > > > u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc) > > { > > return vcpu->arch.tsc_offset + kvm_scale_tsc(vcpu, host_tsc); > > } > > EXPORT_SYMBOL_GPL(kvm_read_l1_tsc); > > > > ... would not it be simpler and more inline with the current code to > > just do what I did above + remove the "+ l1_tsc_offset" + probably > > document tsc_offset ? > > Problem is, I don't think it's correct. :) A good start would be to try > disabling MSR_IA32_TSC interception in KVM, prepare a kvm-unit-tests > test that reads the MSR, and see if you get the host or guest TSC...
I actually just submitted a patch with your original suggestion (I hope) because I realized that adjust tsc was still using the wrong tsc_offset anyway :)
> > Paolo > Amazon Development Center Germany GmbH Berlin - Dresden - Aachen main office: Krausenstr. 38, 10117 Berlin Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger Ust-ID: DE289237879 Eingetragen am Amtsgericht Charlottenburg HRB 149173 B
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