RE: [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info

From: "Kang, Luwei" <luwei.kang@intel.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Strong, Beeman" <beeman.strong@intel.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Robert Hoo <robert.hu@linux.intel.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	Jiri Denemark <jdenemar@redhat.com>,
	"rth@twiddle.net" <rth@twiddle.net>
Subject: RE: [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info
Date: Mon, 21 Sep 2020 07:49:22 +0000	[thread overview]
Message-ID: <CY4PR11MB14473A594C244A5B403ADC26803A0@CY4PR11MB1447.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20200918220255.GB57321@habkost.net>

Hi Eduardo,
    This patch set will remove some limitations of Intel PT CPUID information.
    1. The "IP payloads" feature will disable the Intel PT in guests and it will be coming soon.
    2. To make the live migration safe, we set the Intel PT CPUID as a constant value(Icelake server CPUID). It will mask off the new feature of Intel PT.

    About this issue https://bugzilla.redhat.com/show_bug.cgi?id=1853972, Intel PT is disabled in the guest by default, we should use "-cpu Icelake-Server,+intel-pt" to enable the Intel PT.

Thanks,
Luwei Kang

> -----Original Message-----
> From: Eduardo Habkost <ehabkost@redhat.com>
> Sent: Saturday, September 19, 2020 6:03 AM
> To: Kang, Luwei <luwei.kang@intel.com>
> Cc: pbonzini@redhat.com; rth@twiddle.net; qemu-devel@nongnu.org; Strong,
> Beeman <beeman.strong@intel.com>; Jiri Denemark
> <jdenemar@redhat.com>; Robert Hoo <robert.hu@linux.intel.com>
> Subject: Re: [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info
> 
> Hi Luwei Kang,
> 
> I was looking for info on intel-pt and just saw this series, and it was never
> reviewed or merged (sorry for missing it!).  Is this still the approach we want to
> follow for intel-pt?
> 
> I'm CCing Jiri Denemark because this might be relevant for a libvirt issue related
> to intel-pt we were investigating[1].
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1853972
> 
> 
> On Mon, Mar 30, 2020 at 09:56:09AM +0000, Kang, Luwei wrote:
> > > -----Original Message-----
> > > From: Kang, Luwei <luwei.kang@intel.com>
> > > Sent: Tuesday, February 25, 2020 5:38 AM
> > > To: pbonzini@redhat.com; rth@twiddle.net; ehabkost@redhat.com
> > > Cc: qemu-devel@nongnu.org; Strong, Beeman
> <beeman.strong@intel.com>;
> > > Kang, Luwei <luwei.kang@intel.com>
> > > Subject: [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info
> > >
> > > The Intel PT feature includes some
> > > sub-features(CPUID.(EAX=14H,ECX=0H))
> > > and these sub-features are different on different HW platforms. To
> > > make the live migration safety(get the same CPUID info with same cpu
> > > model on different HW platform), the current Intel PT CPUID
> > > information is set to a constant value(from ICELAKE Server).
> > >
> > > It will block the new feature in the later HW platform. what's more,
> > > the support of "IP payloads" will disable the Intel PT in KVM
> > > guest(patch 1) but it will come soon.
> > >
> > > This patchset remove this limitation and expose all the capabilities
> > > to KVM guest. As it will break the live migration safe, Intel PT
> > > will be masked as unmigratable.
> >
> > Ping.
> >
> > Thanks,
> > Luwei Kang
> >
> > >
> > > Luwei Kang (3):
> > >   i386: Remove the limitation of IP payloads for Intel PT
> > >   i386: Remove the CPUID limitation of Intel PT
> > >   i386: Mark the 'INTEL_PT' CPUID bit as unmigratable
> > >
> > >  target/i386/cpu.c | 69
> > > ++++---------------------------------------------------
> > >  1 file changed, 5 insertions(+), 64 deletions(-)
> > >
> > > --
> > > 1.8.3.1
> >
> 
> --
> Eduardo