From: Paolo Bonzini <pbonzini@redhat.com>
To: "Kang, Luwei" <luwei.kang@intel.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 18:46:31 +0200 [thread overview]
Message-ID: <761a025d-6973-e4ab-df6b-c25a171d1298@redhat.com> (raw)
In-Reply-To: <CY4PR11MB1447BB55E8AF4915CD56655980350@CY4PR11MB1447.namprd11.prod.outlook.com>
On 28/09/20 14:42, Kang, Luwei wrote:
>> 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.
I agree that QEMU would have to learn about LIP. Unlike this patch,
however, x86_cpu_filter_features would have to fail if host LIP != guest
LIP. That is, something like
(ecx_0 & INTEL_PT_IP_LIP)) !=
(env->features[INTEL_PT_ECX_0] & INTEL_PT_IP_LIP)
where "intel-pt-lip" would be a feature in env->features[INTEL_PT_ECX_0].
> 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.
Yes, this would work.
Paolo
next prev parent reply other threads:[~2020-09-28 16:47 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
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 [this message]
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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