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From: Like Xu <like.xu@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>,
	Peter Zijlstra <peterz@infradead.org>
Cc: Kan Liang <kan.liang@linux.intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	eranian@google.com, kvm@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Andi Kleen <andi@firstfloor.org>,
	wei.w.wang@intel.com, luwei.kang@intel.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 04/17] perf: x86/ds: Handle guest PEBS overflow PMI and inject it to guest
Date: Fri, 22 Jan 2021 13:30:20 +0800	[thread overview]
Message-ID: <9fa07da4-8ef4-f1f2-72a0-5d747e283912@linux.intel.com> (raw)
In-Reply-To: <YAHT+zLiIg/oUygZ@google.com>

On 2021/1/16 1:42, Sean Christopherson wrote:
> On Fri, Jan 15, 2021, Xu, Like wrote:
>> On 2021/1/15 2:55, Sean Christopherson wrote:
>>> On Mon, Jan 04, 2021, Like Xu wrote:
>>>> +	 * Note: KVM disables the co-existence of guest PEBS and host PEBS.
>>> By "KVM", do you mean KVM's loading of the MSRs provided by intel_guest_get_msrs()?
>>> Because the PMU should really be the entity that controls guest vs. host.  KVM
>>> should just be a dumb pipe that handles the mechanics of how values are context
>>> switch.
>>
>> The intel_guest_get_msrs() and atomic_switch_perf_msrs()
>> will work together to disable the co-existence of guest PEBS and host PEBS:
>>
>> https://lore.kernel.org/kvm/961e6135-ff6d-86d1-3b7b-a1846ad0e4c4@intel.com/
>>
>> +
>>
>> static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
>> ...
>>      if (nr_msrs > 2 && (msrs[1].guest & msrs[0].guest)) {
>>          msrs[2].guest = pmu->ds_area;
>>          if (nr_msrs > 3)
>>              msrs[3].guest = pmu->pebs_data_cfg;
>>      }
>>
>>     for (i = 0; i < nr_msrs; i++)
>> ...
> 
> Yeah, that's exactly what I'm complaining about.  Splitting the logic for
> determining the guest values is unnecessarily confusing, and as evidenced by the
> PEBS_ENABLE bug, potentially fragile.  Perf should have full knowledge and
> control of what values are loaded for the guest.  And, the above indexing magic
> is nigh impossible to follow and _super_ fragile.

Thanks for pointing this out.

> 
> If we change .guest_get_msrs() to take a struct kvm_pmu pointer, then it can
> generate the full set of guest values by grabbing ds_area and pebs_data_cfg.
> Alternatively, .guest_get_msrs() could take the desired guest MSR values
> directly (ds_area and pebs_data_cfg), but kvm_pmu is vendor agnostic, so I don't
> see any reason to not just pass the pointer.

Hi Peter,

What do you think of us passing a "struct kvm_pmu" pointer (defined in 
arch/x86/include/asm/kvm_host.h) to guest_get_msrs(int *nr) ?

---
thx,likexu


  reply	other threads:[~2021-01-22  5:32 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-04 13:15 [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS Like Xu
2021-01-04 13:15 ` [PATCH v3 01/17] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled Like Xu
2021-01-04 13:15 ` [PATCH v3 02/17] KVM: x86/pmu: Use IA32_PERF_CAPABILITIES to adjust features visibility Like Xu
2021-01-04 13:15 ` [PATCH v3 03/17] KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter Like Xu
2021-01-13 18:06   ` Peter Zijlstra
2021-01-14  1:58     ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 04/17] perf: x86/ds: Handle guest PEBS overflow PMI and inject it to guest Like Xu
2021-01-13 18:22   ` Peter Zijlstra
2021-01-13 18:27     ` Peter Zijlstra
2021-01-14  3:39     ` Xu, Like
2021-01-15 12:01       ` Peter Zijlstra
2021-01-15 14:30         ` Xu, Like
2021-01-15 14:44           ` Peter Zijlstra
2021-01-15 15:12             ` Xu, Like
2021-01-25  8:26             ` Like Xu
2021-01-25 11:47               ` Peter Zijlstra
2021-02-02  6:31                 ` Xu, Like
2021-01-14 18:55   ` Sean Christopherson
2021-01-15  2:49     ` Xu, Like
2021-01-15 17:42       ` Sean Christopherson
2021-01-22  5:30         ` Like Xu [this message]
2021-01-04 13:15 ` [PATCH v3 05/17] KVM: x86/pmu: Reprogram guest PEBS event to emulate guest PEBS counter Like Xu
2021-01-15 11:33   ` Peter Zijlstra
2021-01-15 13:53     ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 06/17] KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS Like Xu
2021-01-05 21:11   ` Sean Christopherson
2021-01-07 12:38     ` Xu, Like
2021-01-15 14:46   ` Peter Zijlstra
2021-01-15 15:29     ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 07/17] KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to manage guest DS buffer Like Xu
2021-01-05 21:16   ` Sean Christopherson
2021-01-08  3:05     ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 08/17] KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS Like Xu
2021-01-04 13:15 ` [PATCH v3 09/17] KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled Like Xu
2021-01-04 13:15 ` [PATCH v3 10/17] KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64 Like Xu
2021-01-04 13:15 ` [PATCH v3 11/17] KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter Like Xu
2021-01-04 13:15 ` [PATCH v3 12/17] KVM: x86/pmu: Disable guest PEBS when counters are cross-mapped Like Xu
2021-01-04 13:15 ` [PATCH v3 13/17] KVM: x86/pmu: Add hook to emulate pebs for cross-mapped counters Like Xu
2021-01-04 13:15 ` [PATCH v3 14/17] KVM: vmx/pmu: Limit pebs_interrupt_threshold in the guest DS area Like Xu
2021-01-04 13:15 ` [PATCH v3 15/17] KVM: vmx/pmu: Rewrite applicable_counters field in guest PEBS records Like Xu
2021-01-04 13:15 ` [PATCH v3 16/17] KVM: x86/pmu: Save guest pebs reset values when pebs is configured Like Xu
2021-01-04 13:15 ` [PATCH v3 17/17] KVM: x86/pmu: Adjust guest pebs reset values for crpss-mapped counters Like Xu
2021-01-14 19:10 ` [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS Sean Christopherson
2021-01-15  2:02   ` Xu, Like
2021-01-15 17:57     ` Sean Christopherson
2021-01-15 18:27       ` Andi Kleen
2021-01-15 18:51         ` Sean Christopherson
2021-01-15 19:11           ` Andi Kleen
2021-01-22  9:56           ` Peter Zijlstra
2021-01-25  8:08             ` Like Xu
2021-01-25 11:13               ` Peter Zijlstra
2021-01-25 12:07                 ` Xu, Like
2021-01-25 12:18                   ` Peter Zijlstra
2021-01-25 12:53                     ` Xu, Like

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