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Message-ID: <4e2eee77-721f-4b0f-a825-a664951640f0@redhat.com>
Date:   Mon, 30 Oct 2023 17:34:17 +0100
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Subject: Re: [PATCH v13 05/35] KVM: PPC: Drop dead code related to
 KVM_ARCH_WANT_MMU_NOTIFIER
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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>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kvmarm@lists.linux.dev, linux-mips@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org,
        linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Anish Moorthy <amoorthy@google.com>,
        David Matlack <dmatlack@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= <mic@digikod.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        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: <20231027182217.3615211-1-seanjc@google.com>
 <20231027182217.3615211-6-seanjc@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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In-Reply-To: <20231027182217.3615211-6-seanjc@google.com>
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On 10/27/23 20:21, Sean Christopherson wrote:
> Assert that both KVM_ARCH_WANT_MMU_NOTIFIER and CONFIG_MMU_NOTIFIER are
> defined when KVM is enabled, and return '1' unconditionally for the
> CONFIG_KVM_BOOK3S_HV_POSSIBLE=n path.  All flavors of PPC support for KVM
> select MMU_NOTIFIER, and KVM_ARCH_WANT_MMU_NOTIFIER is unconditionally
> defined by arch/powerpc/include/asm/kvm_host.h.
> 
> Effectively dropping use of KVM_ARCH_WANT_MMU_NOTIFIER will simplify a
> future cleanup to turn KVM_ARCH_WANT_MMU_NOTIFIER into a Kconfig, i.e.
> will allow combining all of the
> 
>    #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> 
> checks into a single
> 
>    #ifdef CONFIG_KVM_GENERIC_MMU_NOTIFIER
> 
> without having to worry about PPC's "bare" usage of
> KVM_ARCH_WANT_MMU_NOTIFIER.
> 
> 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..b0a512ede764 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -632,12 +632,13 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		break;
>   #endif
>   	case KVM_CAP_SYNC_MMU:
> +#if !defined(CONFIG_MMU_NOTIFIER) || !defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> +		BUILD_BUG();
> +#endif
>   #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>   		r = hv_enabled;
> -#elif defined(KVM_ARCH_WANT_MMU_NOTIFIER)
> -		r = 1;
>   #else
> -		r = 0;
> +		r = 1;
>   #endif
>   		break;
>   #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>