Messages in this thread | | | Subject | Re: [PATCH v4 2/5] KVM: x86: Add IBPB support | From | KarimAllah Ahmed <> | Date | Wed, 31 Jan 2018 18:11:39 +0100 |
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On 01/31/2018 05:50 PM, Jim Mattson wrote: > On Wed, Jan 31, 2018 at 5:10 AM, KarimAllah Ahmed <karahmed@amazon.de> wrote: > >> + vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap, MSR_IA32_PRED_CMD, >> + MSR_TYPE_W); > > Why not disable this intercept eagerly, rather than lazily? Unlike > MSR_IA32_SPEC_CTRL, there is no guest value to save/restore, so there > is no cost to disabling the intercept if the guest cpuid info declares > support for it. > > >> + if (to_vmx(vcpu)->save_spec_ctrl_on_exit) { >> + nested_vmx_disable_intercept_for_msr( >> + msr_bitmap_l1, msr_bitmap_l0, >> + MSR_IA32_PRED_CMD, >> + MSR_TYPE_R); >> + } > > I don't think this should be predicated on > "to_vmx(vcpu)->save_spec_ctrl_on_exit." Why not just > "guest_cpuid_has(vcpu, X86_FEATURE_IBPB)"?
Paolo suggested this on the previous revision because guest_cpuid_has() would be slow.
> Also, the final argument to > nested_vmx_disable_intercept_for_msr should be MSR_TYPE_W rather than > MSR_TYPE_R. > Oops! will fix! 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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