linux-kernel - Re: [RFC 8/9] RISC-V: KVM: Implement perf support

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Message-ID: <Y4oxNbQwOldICdnw@google.com>
Date:   Fri, 2 Dec 2022 17:09:09 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Atish Patra <atishp@...osinc.com>
Cc:     linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Guo Ren <guoren@...nel.org>, kvm-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [RFC  8/9] RISC-V: KVM: Implement perf support

On Mon, Jul 18, 2022, Atish Patra wrote:
> RISC-V SBI PMU & Sscofpmf ISA extension allows supporting perf in
> the virtualization enviornment as well. KVM implementation
> relies on SBI PMU extension for most of the part while traps
> & emulates the CSRs read for counter access.

For the benefit of non-RISCV people, the changelog (and documentation?) should
explain why RISC-V doesn't need to tap into kvm_register_perf_callbacks().
Presumably there's something in the "RISC-V SBI PMU & Sscofpmf ISA extension" spec
that allows hardware to differentiate between events that are for guest vs. host?