linux-kernel - Re: [PATCH v7 09/13] KVM: x86: Implement Intel Processor Trace context switch

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Message-ID: <20180504102958.u6c3mqackl4kzd54@um.fi.intel.com>
Date:   Fri, 4 May 2018 13:29:58 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, pbonzini@...hat.com,
        rkrcmar@...hat.com, linux-kernel@...r.kernel.org, joro@...tes.org,
        peterz@...radead.org, chao.p.peng@...ux.intel.com
Subject: Re: [PATCH v7 09/13] KVM: x86: Implement Intel Processor Trace
 context switch

On Thu, May 03, 2018 at 08:08:39PM +0800, Luwei Kang wrote:
> +static void pt_guest_enter(struct vcpu_vmx *vmx)
> +{
> +	if (pt_mode == PT_MODE_HOST || pt_mode == PT_MODE_HOST_GUEST)
> +		rdmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
> +
> +	if (pt_mode == PT_MODE_HOST_GUEST &&
> +		vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) {
> +		wrmsrl(MSR_IA32_RTIT_CTL, 0);
> +		pt_save_msr(&vmx->pt_desc.host, vmx->pt_desc.range_cnt);
> +		pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.range_cnt);
> +	}
> +}
> +
> +static void pt_guest_exit(struct vcpu_vmx *vmx)
> +{
> +	if (pt_mode == PT_MODE_HOST_GUEST &&
> +		vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) {
> +		pt_save_msr(&vmx->pt_desc.guest, vmx->pt_desc.range_cnt);
> +		pt_load_msr(&vmx->pt_desc.host, vmx->pt_desc.range_cnt);
> +	}
> +
> +	if (pt_mode == PT_MODE_HOST || pt_mode == PT_MODE_HOST_GUEST)
> +		wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
> +}

This means that a host PT event won't get the guest traces and won't get
any notification as to what'd happened or why. At the minimum we need to
send a PARTIAL AUX record at the pt_guest_enter(), when we turn the host
tracing off.

Regards,
--
Alex