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Date:   Wed, 19 Jul 2023 19:34:22 +0200
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To:     Sean Christopherson <seanjc@google.com>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        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>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Alexander Graf <graf@amazon.de>,
        Nicholas Piggin <npiggin@gmail.com>
Cc:     kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kvmarm@lists.linux.dev, linux-mips@vger.kernel.org,
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        Chao Peng <chao.p.peng@linux.intel.com>,
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        Jarkko Sakkinen <jarkko@kernel.org>,
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        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
References: <20230718234512.1690985-1-seanjc@google.com>
 <20230718234512.1690985-5-seanjc@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v11 04/29] KVM: PPC: Drop dead code related to
 KVM_ARCH_WANT_MMU_NOTIFIER
In-Reply-To: <20230718234512.1690985-5-seanjc@google.com>
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On 7/19/23 01:44, Sean Christopherson wrote:
> Signed-off-by: Sean Christopherson<seanjc@google.com>
> ---
>   arch/powerpc/kvm/powerpc.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 7197c8256668..5cf9e5e3112a 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -634,10 +634,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_SYNC_MMU:
>   #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>   		r = hv_enabled;

This could actually be unnecessarily conservative.  Even book3s_pr.c 
knows how to do unmap and set_spte, so it should be able to support 
KVM_CAP_SYNC_MMU.  Alex, Nick, do you remember any of this?  This would 
mean moving KVM_CAP_SYNC_MMU to virt/kvm/kvm_main.c, which is nice.

Paolo

> -#elif defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> -		r = 1;
>   #else
> -		r = 0;
> +#ifndef KVM_ARCH_WANT_MMU_NOTIFIER
> +		BUILD_BUG();
> +#endif
> +		r = 1;
>   #endif
>   		break;
>   #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE