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From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Luwei Kang <luwei.kang@intel.com>,
	kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
	hpa@zytor.com, x86@kernel.org, rkrcmar@redhat.com,
	linux-kernel@vger.kernel.org, joro@8bytes.org,
	chao.p.peng@linux.intel.com
Subject: Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode
Date: Mon, 7 May 2018 12:47:41 +0200	[thread overview]
Message-ID: <6b6a82f9-4bb5-b072-b829-a0903d9366fa@redhat.com> (raw)
In-Reply-To: <20180504221556.GX12217@hirez.programming.kicks-ass.net>

On 05/05/2018 00:15, Peter Zijlstra wrote:
> On Fri, May 04, 2018 at 11:44:09PM +0200, Paolo Bonzini wrote:
>> On 04/05/2018 12:45, Peter Zijlstra wrote:
>>> On Thu, May 03, 2018 at 04:38:23PM +0300, Alexander Shishkin wrote:
>>>> On Thu, May 03, 2018 at 02:50:12PM +0200, Paolo Bonzini wrote:
>>>
>>>>> And you still need the module parameter to decide
>>>>> whether the host is _allowed_ to cause incomplete traces in the guest.
>>>>
>>>> Or rather a parameter to decide who wins in case both host and guest want
>>>> to trace the guest. That's arguably better than having different versions of
>>>> PT in the guest depending on a module parameter setting.
>>>
>>> Yes, that sounds like a much better approach.
>>
>> I don't think so.  The possibility that the host would lose tracing data
>> just because the guest starts using PT seems hideous to me...
> 
> Well, either way around is a fairly crap situation, the modparam at
> least lets the admin pick which it goes. But if you want to always let
> the host win, that's fine with me too, less knobs is better.

I expect that the default "system-wide" host wins will be used almost
always, with "host-guest" being used in case someone actually wants to
use PT in guests.

I agree that "Host-only, drop guest events" should be removed, since it
can be emulated by perf code.  Luwei, can you change that?

Paolo

  reply	other threads:[~2018-05-07 10:47 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-03 12:08 [PATCH v7 00/13] Intel Processor Trace virtualization enabling Luwei Kang
2018-05-03 10:33 ` Alexander Shishkin
2018-05-03 12:08 ` [PATCH v7 01/13] perf/x86/intel/pt: Move Intel-PT MSRs bit definitions to a public header Luwei Kang
2018-05-03 12:08 ` [PATCH v7 02/13] perf/x86/intel/pt: Change pt_cap_get() to a public function Luwei Kang
2018-05-03 12:08 ` [PATCH v7 03/13] perf/x86/intel/pt: Add new bit definitions for Intel PT MSRs Luwei Kang
2018-05-03 12:08 ` [PATCH v7 04/13] perf/x86/intel/pt: add new capability for Intel PT Luwei Kang
2018-05-03 12:08 ` [PATCH v7 05/13] perf/x86/intel/pt: Introduce a new function to get capability of " Luwei Kang
2018-05-03 10:50   ` Alexander Shishkin
2018-05-03 11:04     ` Kang, Luwei
2018-05-03 12:13       ` Alexander Shishkin
2018-05-03 12:30         ` Paolo Bonzini
2018-05-03 12:30         ` Kang, Luwei
2018-05-03 12:32           ` Paolo Bonzini
2018-05-03 12:50             ` Kang, Luwei
2018-05-03 12:59               ` Alexander Shishkin
2018-05-03 12:08 ` [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode Luwei Kang
2018-05-03 11:32   ` Alexander Shishkin
2018-05-03 11:50     ` Paolo Bonzini
2018-05-03 12:02       ` Alexander Shishkin
2018-05-03 12:30         ` Paolo Bonzini
2018-05-03 12:48           ` Alexander Shishkin
2018-05-03 12:50             ` Paolo Bonzini
2018-05-03 13:38               ` Alexander Shishkin
2018-05-03 13:48                 ` Paolo Bonzini
2018-05-04 10:38                   ` Alexander Shishkin
2018-05-04 21:52                     ` Paolo Bonzini
2018-05-04 10:45                 ` Peter Zijlstra
2018-05-04 21:44                   ` Paolo Bonzini
2018-05-04 22:15                     ` Peter Zijlstra
2018-05-07 10:47                       ` Paolo Bonzini [this message]
2018-05-03 11:52     ` Paolo Bonzini
2018-05-03 12:09       ` Alexander Shishkin
2018-05-03 12:31         ` Paolo Bonzini
2018-05-03 12:08 ` [PATCH v7 07/13] KVM: x86: Add Intel Processor Trace cpuid emulation Luwei Kang
2018-05-03 12:08 ` [PATCH v7 08/13] KVM: x86: Add Intel processor trace context for each vcpu Luwei Kang
2018-05-03 11:39   ` Alexander Shishkin
2018-05-03 11:53     ` Paolo Bonzini
2018-05-03 12:08 ` [PATCH v7 09/13] KVM: x86: Implement Intel Processor Trace context switch Luwei Kang
2018-05-04 10:29   ` Alexander Shishkin
2018-05-04 21:49     ` Paolo Bonzini
2018-05-03 12:08 ` [PATCH v7 10/13] KVM: x86: Introduce a function to initialize the PT configuration Luwei Kang
2018-05-03 12:08 ` [PATCH v7 11/13] KVM: x86: Implement Intel Processor Trace MSRs read/write Luwei Kang
2018-05-04 10:11   ` Alexander Shishkin
2018-05-04 21:47     ` Paolo Bonzini
2018-05-03 12:08 ` [PATCH v7 12/13] KVM: x86: Set intercept for Intel PT " Luwei Kang
2018-05-03 12:08 ` [PATCH v7 13/13] KVM: x86: Disable Intel Processor Trace when VMXON in L1 guest Luwei Kang
2018-05-04 10:23   ` Alexander Shishkin
2018-05-04 21:49     ` Paolo Bonzini
2018-05-03 12:13 [PATCH v7 00/13] Intel Processor Trace virtualization enabling Luwei Kang
2018-05-03 12:13 ` [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode Luwei Kang

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