From: "Kang, Luwei" <luwei.kang@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Eduardo Habkost <ehabkost@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"Strong, Beeman" <beeman.strong@intel.com>,
"rth@twiddle.net" <rth@twiddle.net>
Subject: RE: [PATCH v1 1/3] i386: Remove the limitation of IP payloads for Intel PT
Date: Mon, 28 Sep 2020 12:42:37 +0000 [thread overview]
Message-ID: <CY4PR11MB1447BB55E8AF4915CD56655980350@CY4PR11MB1447.namprd11.prod.outlook.com> (raw)
In-Reply-To: <d85a3245-c774-5098-5d14-2e3b3a2eda18@redhat.com>
> >>>> No, it's not possible. KVM doesn't have a say on what the
> >>>> processor writes in the tracing packets.
> >>> Can KVM refuse to enable packet generation if CSbase is not zero and
> >>> CPUID.(EAX=14H,ECX=0)[bit 31] seen by guest is different from host?
> >>
> >> Yes, but the processor could change operating mode (and hence CSbase)
> >> while tracing is active. This is very unlikely, since it would
> >> require nonzero CS-base and a 32-bit host, but in principle not
> >> impossible (could be a firmware call, for example).
> >>
> >> The only solution is for KVM to accept both, and for QEMU to refuse a
> >> setting that does not match the host.
> >>
> >
> > So I need to add a patch in KVM to disabled the Intel PT when the
> > CSbase is not zero and the guest LIP different from the host. And this
> > limitation in qemu (disabled the PT when LIP is enabled in the host)
> > can be remove. Is that right?
>
> No, if a feature cannot be emulated, that means it cannot be enabled unless it
> matches the host. That's generally not a problem since Intel PT is usually used
> only with "-cpu host".
>
The limitation of LIP in qemu will mask off the Intel PT in KVM guest even with "-cpu host". e.g. This bit will be set in SnowRidge HW and later.
How about "-cpu cpu_model, +intel-pt" use case? The current value of Intel PT CPUID is a constant. Can we make the ICX CPUID as basic inforation(LIP is 0) and using "+intel-pt-lip" to make Intel PT work on the CPU which LIP is 1 on the host? As you mentioned before, Intel PT cannot be enabled in guest unless it matches the host.
Thanks,
Luwei Kang
next prev parent reply other threads:[~2020-09-28 13:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-24 21:38 [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info Luwei Kang
2020-02-24 21:38 ` [PATCH v1 1/3] i386: Remove the limitation of IP payloads for Intel PT Luwei Kang
2020-09-25 16:15 ` Eduardo Habkost
2020-09-25 16:42 ` Strong, Beeman
2020-09-25 16:54 ` Eduardo Habkost
2020-09-25 20:23 ` Paolo Bonzini
2020-09-25 20:29 ` Eduardo Habkost
2020-09-25 20:40 ` Paolo Bonzini
2020-09-28 5:19 ` Kang, Luwei
2020-09-28 7:35 ` Paolo Bonzini
2020-09-28 12:42 ` Kang, Luwei [this message]
2020-09-28 14:12 ` Eduardo Habkost
2020-09-29 2:28 ` Kang, Luwei
2020-09-29 3:44 ` Eduardo Habkost
2020-09-28 16:46 ` Paolo Bonzini
2020-09-29 2:28 ` Kang, Luwei
2020-02-24 21:38 ` [PATCH v1 2/3] i386: Remove the CPUID limitation of " Luwei Kang
2020-02-24 21:38 ` [PATCH v1 3/3] i386: Mark the 'INTEL_PT' CPUID bit as unmigratable Luwei Kang
2020-03-30 9:56 ` [PATCH v1 0/3] Remove the limitation of Intel PT CPUID info Kang, Luwei
2020-09-18 22:02 ` Eduardo Habkost
2020-09-21 7:49 ` Kang, Luwei
2020-09-21 16:50 ` Eduardo Habkost
2020-09-23 2:52 ` Kang, Luwei
2020-09-23 14:15 ` Eduardo Habkost
2020-09-24 12:47 ` Kang, Luwei
2020-09-24 13:34 ` Eduardo Habkost
2020-09-25 8:20 ` Kang, Luwei
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