linux-kernel - Re: [PATCH] KVM: Use consistent type for return value of kvm_mmu_memory_cache_nr_free

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Message-ID: <YqiigqccucuU2AQg@google.com>
Date:   Tue, 14 Jun 2022 15:00:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Bo Liu <liubo03@...pur.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Use consistent type for return value of
 kvm_mmu_memory_cache_nr_free_objects()

On Tue, Jun 14, 2022, Bo Liu wrote:
> The return value type of the function rmap_can_add() is "bool", and it will
> returns the result of the function kvm_mmu_memory_cache_nr_free_objects().
> So we should change the return value type of
> kvm_mmu_memory_cache_nr_free_objects() to "bool".
> 
> Signed-off-by: Bo Liu <liubo03@...pur.com>
> ---
>  include/linux/kvm_host.h | 2 +-
>  virt/kvm/kvm_main.c      | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c20f2d55840c..a399a7485795 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1358,7 +1358,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm);
>  
>  #ifdef KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE
>  int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min);
> -int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc);
> +bool kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc);
>  void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc);
>  void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
>  #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a67e996cbf7f..2872569e3580 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -394,9 +394,9 @@ int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min)
>  	return 0;
>  }
>  
> -int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc)
> +bool kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc)

Absolutely not, the name of the function is "nr_free_objects".  Renaming it to
"has_free_objects" is not a net positive IMO.  If we really care about returning
a bool then we can tweak rmap_can_add().

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 17252f39bd7c..047855d134da 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1018,7 +1018,7 @@ static bool rmap_can_add(struct kvm_vcpu *vcpu)
        struct kvm_mmu_memory_cache *mc;

        mc = &vcpu->arch.mmu_pte_list_desc_cache;
-       return kvm_mmu_memory_cache_nr_free_objects(mc);
+       return !!kvm_mmu_memory_cache_nr_free_objects(mc);
 }

 static void rmap_remove(struct kvm *kvm, u64 *spte)