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

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Date:   Wed, 21 Sep 2016 10:33:08 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wincy Van <fanwenyi0529@...il.com>,
        Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH v2] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv

2016-09-20 21:06 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2016-09-20 08:35+0800, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> 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@...il.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Wincy Van <fanwenyi0529@...il.com>
>> Cc: Yang Zhang <yang.zhang.wz@...il.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>> 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. :)

Regards,
Wanpeng Li