From: Wei Wang <wei.w.wang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
pbonzini@redhat.com, ak@linux.intel.com, kan.liang@intel.com,
mingo@redhat.com, rkrcmar@redhat.com, like.xu@intel.com,
jannh@google.com, arei.gonglei@huawei.com, jmattson@google.com
Subject: Re: [PATCH v7 08/12] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack
Date: Wed, 10 Jul 2019 16:19:30 +0800 [thread overview]
Message-ID: <5D259F92.6030107@intel.com> (raw)
In-Reply-To: <20190709121912.GY3402@hirez.programming.kicks-ass.net>
On 07/09/2019 08:19 PM, Peter Zijlstra wrote:
>
>> For the lbr feature, could we thought of it as first come, first served?
>> For example, if we have 2 host threads who want to use lbr at the same time,
>> I think one of them would simply fail to use.
>>
>> So if guest first gets the lbr, host wouldn't take over unless some
>> userspace command (we added to QEMU) is executed to have the vCPU
>> actively stop using lbr.
> Doesn't work that way.
>
> Say you start KVM with LBR emulation, it creates this task event, it
> gets the LBR (nobody else wants it) and the guest works and starts using
> the LBR.
>
> Then the host creates a CPU LBR event and the vCPU suddenly gets denied
> the LBR and the guest no longer functions correctly.
>
> Or you should fail to VMENTER, in which case you starve the guest, but
> at least it doesn't malfunction.
>
Ok, I think we could go with the first option for now, like this:
When there are other host threads starting to use lbr, host perf notifies
kvm to disable the guest use of lbr (add a notifier_block), which includes:
- cancel passing through lbr msrs to guest
- upon guest access to the lbr msr (will trap to KVM now), return #GP
(or 0).
Best,
Wei
next prev parent reply other threads:[~2019-07-10 8:14 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 1:23 [PATCH v7 00/12] Guest LBR Enabling Wei Wang
2019-07-08 1:23 ` [PATCH v7 01/12] perf/x86: fix the variable type of the LBR MSRs Wei Wang
2019-07-08 1:23 ` [PATCH v7 02/12] perf/x86: add a function to get the lbr stack Wei Wang
2019-07-08 1:23 ` [PATCH v7 03/12] KVM/x86: KVM_CAP_X86_GUEST_LBR Wei Wang
2019-07-08 1:23 ` [PATCH v7 04/12] KVM/x86: intel_pmu_lbr_enable Wei Wang
2019-07-08 1:23 ` [PATCH v7 05/12] KVM/x86/vPMU: tweak kvm_pmu_get_msr Wei Wang
2019-07-08 1:23 ` [PATCH v7 06/12] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest Wei Wang
2019-07-08 1:23 ` [PATCH v7 07/12] perf/x86: no counter allocation support Wei Wang
2019-07-08 14:29 ` Peter Zijlstra
2019-07-09 2:58 ` Wei Wang
2019-07-09 9:43 ` Peter Zijlstra
2019-07-09 11:36 ` Wei Wang
2019-07-08 1:23 ` [PATCH v7 08/12] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack Wei Wang
2019-07-08 14:48 ` Peter Zijlstra
2019-07-09 3:04 ` Wei Wang
2019-07-09 9:39 ` Peter Zijlstra
2019-07-09 11:34 ` Wei Wang
2019-07-09 12:19 ` Peter Zijlstra
2019-07-10 8:19 ` Wei Wang [this message]
2019-07-09 11:45 ` Peter Zijlstra
2019-07-10 8:21 ` Wei Wang
2019-07-08 1:23 ` [PATCH v7 09/12] perf/x86: save/restore LBR_SELECT on vCPU switching Wei Wang
2019-07-08 1:23 ` [PATCH v7 10/12] KVM/x86/lbr: lazy save the guest lbr stack Wei Wang
2019-07-08 14:53 ` Peter Zijlstra
2019-07-08 15:11 ` Andi Kleen
2019-07-09 11:39 ` Peter Zijlstra
2019-07-09 3:14 ` Wei Wang
2019-07-08 1:23 ` [PATCH v7 11/12] KVM/x86: remove the common handling of the debugctl msr Wei Wang
2019-07-08 1:23 ` [PATCH v7 12/12] KVM/VMX/vPMU: support to report GLOBAL_STATUS_LBRS_FROZEN Wei Wang
2019-07-08 15:09 ` Peter Zijlstra
2019-07-09 3:24 ` Wei Wang
2019-07-09 11:35 ` Peter Zijlstra
2019-07-10 9:23 ` Wei Wang
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