linux-kernel - Re: [PATCH 0/9] Intel Processor Trace virtulization enabling

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Message-ID: <109396fa-8f7c-8f24-e804-2a5b71ef0c64@redhat.com>
Date:   Mon, 23 Oct 2017 16:40:13 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Kang, Luwei" <luwei.kang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: Re: [PATCH 0/9] Intel Processor Trace virtulization enabling

On 23/10/2017 10:01, Kang, Luwei wrote:
> 
>>> So, can we enable it in L1
>>> guest only first?  I think it is not worth to disable EPT for L1 to
>>> enable intel PT. what is your opinion?
>> Yes, we can enable it.  But since KVM sets IA32_VMX_MISC[14]=0, your patches must forbid enabling processor trace during VMX
>> operation.
>
> L1 hypervisor can't  get the capability of " TraceEn can be set in
> VMX operation (IA32_VMX_MISC[bit 14] is 0)" and set it to 0. We need
> to trap whether L1 hypervisor have enable VMXON, and forbid enable PT
> when vmxon. Is that right? Or have something else?

Correct.  I don't have the SDM at hand, so I'm not sure what happens if
you do a VMXON while TraceEn is 1.  However, that has to be handled as well.

Paolo