linux-kernel - RE: [PATCH v13 08/12] KVM: x86: Add Intel PT context switch for each vcpu

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Date:   Thu, 25 Oct 2018 00:06:25 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "songliubraving@...com" <songliubraving@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
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        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "marcorr@...gle.com" <marcorr@...gle.com>,
        "ubizjak@...il.com" <ubizjak@...il.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: RE: [PATCH v13 08/12] KVM: x86: Add Intel PT context switch for
 each vcpu

> > +static void pt_guest_enter(struct vcpu_vmx *vmx) {
> > +	if (pt_mode == PT_MODE_SYSTEM)
> > +		return;
> > +
> > +	/* Save host state before VM entry */
> > +	rdmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
> > +
> > +	/*
> > +	 * Set guest state of MSR_IA32_RTIT_CTL MSR (PT will be disabled
> > +	 * on VM entry when it has been disabled in guest before).
> > +	 */
> > +	vmcs_write64(GUEST_IA32_RTIT_CTL, vmx->pt_desc.guest.ctl);
> > +
> > +	if (vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) {
> > +		wrmsrl(MSR_IA32_RTIT_CTL, 0);
> > +		pt_save_msr(&vmx->pt_desc.host, vmx->pt_desc.addr_range);
> > +		pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.addr_range);
> > +	}
> > +}
> 
> From my side this is still a NAK, because [1].
> 
> [1] https://marc.info/?l=kvm&m=153847567226248&w=2
> 

This place is save the host PT status and load the guest PT status before VM-entry when working in Host-Guest mode.

Thanks,
Luwei Kang