linux-kernel - Re: [PATCH] KVM: VMX: enable LBR virtualization

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Message-ID: <56204AD0.7030509@huawei.com>
Date:	Fri, 16 Oct 2015 08:54:40 +0800
From:	Jian Zhou <jianjay.zhou@...wei.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, <herongguang.he@...wei.com>,
	<zhang.zhanghailiang@...wei.com>, <gleb@...nel.org>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
	<x86@...nel.org>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC:	<weidong.huang@...wei.com>, <peter.huangpeng@...wei.com>
Subject: Re: [PATCH] KVM: VMX: enable LBR virtualization

>>> Does it depend on vPMU _for Linux guests_ or in general?  My impression
>>> is that LBR can be used by the guest independent of the PMU.
>>
>>    I think only for Linux guests.
>>
>>    I googled how to enable LBR on other guests(except Linux guests),
>>    e.g. Windows, and got no developer manuals about it.
>>
>>    Here is an article about it:
>>    http://www.codeproject.com/Articles/517466/Last-branch-records-
>>    and-branch-tracing
>>    it says:
>>    "bit 8 of DR7 represents bit 0 of DebugCtl. This is the LBR bit."
>
> Don't worry about the operating system in the guest: you are just
> emulating a processor feature, you do not care about anything except
> what is written in the Intel SDM.
>
> You can use kvm-unit-tests
> (https://git.kernel.org/cgit/virt/kvm/kvm-unit-tests.git/) to write a
> test for your feature.  There are existing tests for debugging features.

   ok.

   Regards,

   Jian

>
>
>

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