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Date:   Thu, 20 Jul 2023 09:15:41 +0800
From:   Yuan Yao <yuan.yao@linux.intel.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
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        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Moore <paul@paul-moore.com>,
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        "Serge E. Hallyn" <serge@hallyn.com>, kvm@vger.kernel.org,
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        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC PATCH v11 05/29] KVM: Convert KVM_ARCH_WANT_MMU_NOTIFIER to
 CONFIG_KVM_GENERIC_MMU_NOTIFIER
Message-ID: <20230720011541.6ti5sygwwfwko6ab@yy-desk-7060>
References: <20230718234512.1690985-1-seanjc@google.com>
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 <ZLfv7aRq5W52ezek@google.com>
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On Wed, Jul 19, 2023 at 07:15:09AM -0700, Sean Christopherson wrote:
> On Wed, Jul 19, 2023, Yuan Yao wrote:
> > On Tue, Jul 18, 2023 at 04:44:48PM -0700, Sean Christopherson wrote:
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 90a0be261a5c..d2d3e083ec7f 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -255,7 +255,9 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > >  #endif
> > >
> > > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > > +struct kvm_gfn_range;
> >
> > Not sure why a declaration here, it's defined for ARCHs which defined
> > KVM_ARCH_WANT_MMU_NOTIFIER before.
>
> The forward declaration exists to handle cases where CONFIG_KVM=n, specifically
> arch/powerpc/include/asm/kvm_ppc.h's declaration of hooks to forward calls to
> uarch modules:
>
> 	bool (*unmap_gfn_range)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*test_age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*set_spte_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
>
> Prior to using a Kconfig, a forward declaration wasn't necessary because
> arch/powerpc/include/asm/kvm_host.h would #define KVM_ARCH_WANT_MMU_NOTIFIER even
> if CONFIG_KVM=n.
>
> Alternatively, kvm_ppc.h could declare the struct.  I went this route mainly to
> avoid the possibility of someone encountering the same problem on a different
> architecture.

Ah I see, thanks for your explanation!