linux-kernel - Re: [PATCH v7 12/12] KVM/VMX/vPMU: support to report GLOBAL_STATUS_LBRS

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Message-ID: <20190708150909.GP3402@hirez.programming.kicks-ass.net>
Date:   Mon, 8 Jul 2019 17:09:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, ak@...ux.intel.com, kan.liang@...el.com,
        mingo@...hat.com, rkrcmar@...hat.com, like.xu@...el.com,
        jannh@...gle.com, arei.gonglei@...wei.com, jmattson@...gle.com
Subject: Re: [PATCH v7 12/12] KVM/VMX/vPMU: support to report
 GLOBAL_STATUS_LBRS_FROZEN

On Mon, Jul 08, 2019 at 09:23:19AM +0800, Wei Wang wrote:
> This patch enables the LBR related features in Arch v4 in advance,
> though the current vPMU only has v2 support. Other arch v4 related
> support will be enabled later in another series.
> 
> Arch v4 supports streamlined Freeze_LBR_on_PMI. According to the SDM,
> the LBR_FRZ bit is set to global status when debugctl.freeze_lbr_on_pmi
> has been set and a PMI is generated. The CTR_FRZ bit is set when
> debugctl.freeze_perfmon_on_pmi is set and a PMI is generated.

(that's still a misnomer; it is: freeze_perfmon_on_overflow)

Why?

Who uses that v4 crud? It's broken. It looses events between overflow
and PMI.