linux-kernel - RE: [patch v2 3/8] KVM: x86: add Intel processor trace virtualization mode

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Message-ID: <82D7661F83C1A047AF7DC287873BF1E167E37638@SHSMSX101.ccr.corp.intel.com>
Date:   Tue, 14 Nov 2017 07:31:51 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.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 v2 3/8] KVM: x86: add Intel processor trace
 virtualization mode

> > +	if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_PT_USE_GPA) ||
> > +		!(_vmexit_control & VM_EXIT_CLEAR_IA32_RTIT_CTL) ||
> > +		!(_vmentry_control & VM_ENTRY_LOAD_IA32_RTIT_CTL)) {
> > +		_cpu_based_2nd_exec_control &= ~SECONDARY_EXEC_PT_USE_GPA;
> 
> Also, you are not checking anywhere if the SUPPRESS_PIP controls are available.  This is probably the best place.

SUPPRESS_PIP(should be "CONCEAL", will fix it.) is use for control of  processor trace packet. 
I think we should clear it when in SYSTEM mode (For example, PIPs are generated on VM exit, with NonRoot=0. On VM exit to SMM, VMCS packets are additionally generated). Why need check this here?

> 
> > +		_vmexit_control &= ~VM_EXIT_CLEAR_IA32_RTIT_CTL;
> > +		_vmentry_control &= ~VM_ENTRY_LOAD_IA32_RTIT_CTL;
> 
> These two are not needed; disabling SECONDARY_EXEC_PT_USE_GPA is enough.
> The tracing mode will revert to PT_SYSTEM, which does not use the load/clear RTIT_CTL controls.
> 

The status of *_RTIT_CTL should be same with SECONDARY_EXEC_PT_USE_GPA or would cause VM-entry failed. (architecture-instruction-set-extensions-programming-reference  5.2.3)