linux-kernel - Re: [PATCH] KVM: Add the missing stub function for kvm_dirty_ring_check

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Message-ID: <ZBN0pFN/nF8G3fWl@google.com>
Date:   Thu, 16 Mar 2023 19:57:24 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "gshan@...hat.com" <gshan@...hat.com>,
        "maz@...nel.org" <maz@...nel.org>
Subject: Re: [PATCH] KVM: Add the missing stub function for kvm_dirty_ring_check_request()

On Thu, Mar 16, 2023, Shameerali Kolothum Thodi wrote:
> > From: Sean Christopherson [mailto:seanjc@...gle.com]
> > On Thu, Mar 16, 2023, Shameer Kolothum wrote:
> > > The stub for !CONFIG_HAVE_KVM_DIRTY_RING case is missing.
> > 
> > No stub is needed.  kvm_dirty_ring_check_request() isn't called from
> > common code,
> > and should not (and isn't unless I'm missing something) be called from arch
> > code
> > unless CONFIG_HAVE_KVM_DIRTY_RING=y.
> > 
> > x86 and arm64 are the only users, and they both select
> > HAVE_KVM_DIRTY_RING
> > unconditionally when KVM is enabled.
> 
> Yes, it is at present not called from anywhere other than x86 and arm64.
> But I still think since it is a common helper, better to have a stub.

Why?  It buys us nothing other than dead code, and even worse it could let a bug
that would otherwise be caught during build time escape to run time.