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From: "Mika Penttilä" <mika.penttila@nextfour.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kvm <kvm@vger.kernel.org>, "Wanpeng Li" <wanpeng.li@hotmail.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Wincy Van" <fanwenyi0529@gmail.com>,
	"Yang Zhang" <yang.zhang.wz@gmail.com>
Subject: Re: [PATCH] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv
Date: Thu, 15 Sep 2016 07:46:05 +0300	[thread overview]
Message-ID: <2c892ef7-9548-3765-1818-23a4ae885c4e@nextfour.com> (raw)
In-Reply-To: <CANRm+Cy_om4QHU0TyEipeZmmAGhw+uGkXQjNXXQBpUqXHtUTnA@mail.gmail.com>

On 09/15/2016 07:25 AM, Wanpeng Li wrote:
> 2016-09-15 12:08 GMT+08:00 Mika Penttilä <mika.penttila@nextfour.com>:
>> On 09/14/2016 10:58 AM, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpeng.li@hotmail.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.
>>>
>>
>> While at it, is the vmx flexpriotity stuff still valid code?
>> AFAICS it gets enabled iff TPR shadow is on. flexpriority
>> is on when :
>>
>> (flexpriority_enabled && lapic_in_kernel && cpu_has_vmx_tpr_shadow && cpu_has_vmx_virtualize_apic_accesses)
>>
>> But apic accesses to TPR mmio are not then trapped and TPR changes not reported because
>> the “use TPR shadow” VM-execution control is 1.
> 
> Please note the patch is for MSR-BASED TPR shadow w/o APICv, TPR
> shadow can work correctly in other configurations.
> 
> Regards,
> Wanpeng Li
> 

Hi,

Yes I see, this is slightly offtopic but while at flexpriority, how is it relevant in current kvm?
In other words I see it as dead code, because it is enabled only when TPR shadow is enabled,
and as such ineffective because TPR shadow disables the wmexits tpr reporting uses.

Thanks,
Mika

  reply	other threads:[~2016-09-15 16:20 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-14  7:58 [PATCH] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv Wanpeng Li
2016-09-14  9:40 ` Paolo Bonzini
2016-09-14 12:03   ` Radim Krčmář
2016-09-15  1:19     ` Wanpeng Li
2016-09-15  6:29       ` Paolo Bonzini
2016-09-15  6:40         ` Wanpeng Li
2016-09-15  7:05     ` Wanpeng Li
2016-09-15 15:58       ` Radim Krčmář
2016-09-18  6:53         ` Wanpeng Li
2016-09-18  6:55           ` Wanpeng Li
2016-09-19 13:44           ` Radim Krčmář
2016-09-20  0:18             ` Wanpeng Li
2016-09-22  6:48             ` Wanpeng Li
2016-09-15  0:07   ` Wanpeng Li
2016-09-15  0:17     ` Wanpeng Li
2016-09-15  4:08 ` Mika Penttilä
2016-09-15  4:25   ` Wanpeng Li
2016-09-15  4:46     ` Mika Penttilä [this message]
2016-09-15  6:30   ` Paolo Bonzini

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