linux-kernel - Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks

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Date:   Mon, 20 Sep 2021 13:22:04 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Guo Ren <guoren@...nel.org>, Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-csky@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Artem Kashkanov <artem.kashkanov@...el.com>,
        Like Xu <like.xu.linux@...il.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Subject: Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks

On Mon, 20 Sep 2021 13:05:25 +0100,
Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
> On 17/09/21 09:28, Peter Zijlstra wrote:
> >> In theory, I like the idea of burying intel_pt inside x86 (and even in
> >> Intel+VMX code for the most part), but the actual implementation is a
> >> bit gross.  Because of the whole "KVM can be a module" thing,
> > 
> > ARGH!! we should really fix that. I've heard other archs have made much
> > better choices here.
> 
> I think that's only ARM, and even then it is only because of
> limitations of the hardware which mostly apply only if VHE is not in
> use.
> 
> If anything, it's ARM that should support module build in VHE mode
> (Linux would still need to know whether it will be running at EL1 or
> EL2, but KVM's functionality is as self-contained as on x86 in the VHE
> case).

I don't see this happening anytime soon. At least not before we
declare the arm64 single kernel image policy to be obsolete.

	M.

-- 
Without deviation from the norm, progress is not possible.