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

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Date:   Mon, 13 Nov 2017 17:32:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luwei Kang <luwei.kang@...el.com>, kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.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

On 30/10/2017 23:05, Luwei Kang wrote:
> +	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.

> +		_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.

Paolo

> +	}
> +