linux-kernel - Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS

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Message-ID: <YA62/DV7reRvVyYk@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Jan 2021 13:18:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Xu, Like" <like.xu@...el.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Andi Kleen <andi@...stfloor.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, eranian@...gle.com,
        kvm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, wei.w.wang@...el.com,
        luwei.kang@...el.com, linux-kernel@...r.kernel.org,
        Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS
 via DS

On Mon, Jan 25, 2021 at 08:07:06PM +0800, Xu, Like wrote:

> So under the premise that counter cross-mapping is allowed,
> how can hypercall help fix it ?

Hypercall or otherwise exposing the mapping, will let the guest fix it
up when it already touches the data. Which avoids the host from having
to access the guest memory and is faster, no?