linux-kernel - Re: [PATCH v8 07/26] KVM: x86/pmu: Apply "fast" RDPMC only to Intel PMUs

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Message-ID: <ZU5DZ110JPvcmZp0@google.com>
Date:   Fri, 10 Nov 2023 06:51:19 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Like Xu <likexu@...cent.com>
Subject: Re: [PATCH v8 07/26] KVM: x86/pmu: Apply "fast" RDPMC only to Intel PMUs

On Fri, Nov 10, 2023, Dapeng Mi wrote:
> 
> On 11/10/2023 10:12 AM, Sean Christopherson wrote:
> > Move the handling of "fast" RDPMC instructions, which drop bits 63:31 of
> 
> 63:32?

Oof, yeah.

> > @@ -55,12 +59,17 @@ static struct kvm_pmc *intel_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
> >   	}
> >   }
> > +static u32 intel_rdpmc_get_masked_idx(struct kvm_pmu *pmu, u32 idx)
> 
> inline?

No, for functions that are visible only to the local compilation unit, there's
no reason to use "inline".  "inline" is just a hint, and modern compilers are
smart enough to inline functions when appropriate without a hint, e.g. gcc and
clang inline this on all my configurations.  Compilers may also ignore the hint,
e.g. KASAN=y tends to produce some really amusing results.

A longer explanation/rant here: https://lore.kernel.org/all/ZAdfX+S323JVWNZC@google.com