[PATCH v7 03/23] KVM: Allow KVM implementations to switch off MMIO independent of Kconfig

[Steffen Eiden]

On Wed, Sep 02, 2026 at 09:30:17AM +0100, Marc Zyngier wrote:
> On Wed, 02 Sep 2026 01:38:53 +0100,
> Sean Christopherson <seanjc at google.com> wrote:
> > 
> > On Mon, Aug 31, 2026, Steffen Eiden wrote:
> > > Only defining KVM_MMIO is not flexible enough for multi-KVM systems
> > > where one KVM implements MMIO but others do not. Solve this by
> > > additionally testing for the non-existence of KVM_NO_MMIO before
> > > including MMIO code to KVM.
> > 
> > Ewwwww.  IIUC, s390 ends up with two KVM modules, i.e. there really are two different
> > KVMs being built.  Rather than have a KVM_MMIO and NO_KVM_MMIO, I vote very
> > strongly to drop CONFIG_KVM_MMIO entirely and replace it with __KVM_HAVE_ARCH_MMIO,
> > a la __KVM_HAVE_ARCH_VM_FREE and others.  Tracking two separate macros is going
> > to be annoying to maintain, and will definitely be confusing for non-s390 people.
> > 
> > It'll mean linking in an emtpy coalesced_mmio.o on s390 when building without arm64
> > support, but I'm guessing that won't be at all common for s390 builds.
> > 
> 
> I ended-up doing something very similar locally, because I couldn't
> really make head or tail of the logic while being in holiday mode
> (which doesn't help). However, I kept the negative logic, so that we
> don't need to add anything to any architecture but S390 (they are the
> odd one out here).
negative makes sense. 
IIRC KVM/power does select KVM_MMIO most of the times but not always.
I'll check that.

> 
> Untested hack follows.
> 
> 	M.

Thanks!
I'll verify and integrate it

	Steffen

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