linux-kernel - Re: [PATCH v7 13/13] KVM: x86: Disable Intel Processor Trace when VMXON in L1 guest

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Message-ID: <42da55ab-aefb-aa3c-bfed-d6f0457db798@redhat.com>
Date:   Fri, 4 May 2018 23:49:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Luwei Kang <luwei.kang@...el.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, joro@...tes.org,
        peterz@...radead.org, chao.p.peng@...ux.intel.com
Subject: Re: [PATCH v7 13/13] KVM: x86: Disable Intel Processor Trace when
 VMXON in L1 guest

On 04/05/2018 12:23, Alexander Shishkin wrote:
>> Currently, Intel Processor Trace do not support tracing in L1 guest
>> VMX operation(IA32_VMX_MISC[bit 14] is 0). As mentioned in SDM,
> I don't understand this patch. You mention VMX_MISC[14] here, but I
> can't see anything related to it in the code.

This is talking about the _guest_'s view of IA32_VMX_MISC.  The code
does nothing to set it, so the patch does what the commit message says
below:

>> on these type of processors, execution of the VMXON instruction will
>> clears IA32_RTIT_CTL.TraceEn and any attempt to write IA32_RTIT_CTL
>> causes a general-protection exception (#GP).
>>
>> Signed-off-by: Luwei Kang <luwei.kang@...el.com>

Thanks,

Paolo