Re: [PATCH v2] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv

From: Wanpeng Li
Date: Tue Sep 20 2016 - 22:33:16 EST

2016-09-20 21:06 GMT+08:00 Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>:
> 2016-09-20 08:35+0800, Wanpeng Li:
>> From: Wanpeng Li <>
>> I observed that kvmvapic(to optimize flexpriority=N or AMD) is used
>> to boost TPR access when testing kvm-unit-test/eventinj.flat tpr case
>> on my haswell desktop (w/ flexpriority, w/o APICv). Commit (8d14695f9542
>> x86, apicv: add virtual x2apic support) disable virtual x2apic mode
>> completely if w/o APICv, and the author also told me that windows guest
>> can't enter into x2apic mode when he developed the APICv feature several
>> years ago. However, it is not truth currently, Interrupt Remapping and
>> vIOMMU is added to qemu and the developers from Intel test windows 8 can
>> work in x2apic mode w/ Interrupt Remapping enabled recently.
>> This patch enables TPR shadow for virtual x2apic mode to boost
>> windows guest in x2apic mode even if w/o APICv.
>> Can pass the kvm-unit-test.
>> Suggested-by: Wincy Van <fanwenyi0529@xxxxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
>> Cc: Wincy Van <fanwenyi0529@xxxxxxxxx>
>> Cc: Yang Zhang <yang.zhang.wz@xxxxxxxxx>
>> Signed-off-by: Wanpeng Li <>
>> ---
>> v1 -> v2:
>> * leverage the cached msr bitmap
> V2 has a similar bug as V1 ... we have to intercept most MSRs when the
> APICv is disabled for selected VCPU, but globally enabled.
> We need at least 2 sets of bitmaps for x2apic: one for
> "enable_apicv && kvm_vcpu_apicv_active()"
> the other for
> "enable_apicv && !kvm_vcpu_apicv_active()"
> and "!enable_apicv"
> and use the correct one in vmx_set_msr_bitmap().

Agreed, please review v3. :)

Wanpeng Li