linux-kernel - Re: [PATCH 10/21] KVM: x86/mmu: Make __GFP

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Date:   Wed, 10 Jun 2020 11:57:32 -0700
From:   Ben Gardon <bgardon@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Marc Zyngier <maz@...nel.org>, Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Feiner <pfeiner@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH 10/21] KVM: x86/mmu: Make __GFP_ZERO a property of the
 memory cache

On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Add a gfp_zero flag to 'struct kvm_mmu_memory_cache' and use it to
> control __GFP_ZERO instead of hardcoding a call to kmem_cache_zalloc().
> A future patch needs such a flag for the __get_free_page() path, as
> gfn arrays do not need/want the allocator to zero the memory.  Convert
> the kmem_cache paths to __GFP_ZERO now so as to avoid a weird and
> inconsistent API in the future.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Ben Gardon <bgardon@...gle.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/mmu/mmu.c          | 7 ++++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e7a427547557..fb99e6776e27 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -251,6 +251,7 @@ struct kvm_kernel_irq_routing_entry;
>   */
>  struct kvm_mmu_memory_cache {
>         int nobjs;
> +       gfp_t gfp_zero;
This would make more sense to me if it could be used for general extra
gfp flags and was called gfp_flags or something, or it was a boolean
that was later translated into the flag being set. Storing the
gfp_zero flag here is a little counter-intuitive. Probably not worth
changing unless you're sending out a v2 for some other reason.

>         struct kmem_cache *kmem_cache;
>         void *objects[KVM_NR_MEM_OBJS];
>  };
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index d245acece3cd..6b0ec9060786 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1063,8 +1063,10 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
>  static inline void *mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache *mc,
>                                                gfp_t gfp_flags)
>  {
> +       gfp_flags |= mc->gfp_zero;
> +
>         if (mc->kmem_cache)
> -               return kmem_cache_zalloc(mc->kmem_cache, gfp_flags);
> +               return kmem_cache_alloc(mc->kmem_cache, gfp_flags);
>         else
>                 return (void *)__get_free_page(gfp_flags);
>  }
> @@ -5680,7 +5682,10 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
>         int ret;
>
>         vcpu->arch.mmu_pte_list_desc_cache.kmem_cache = pte_list_desc_cache;
> +       vcpu->arch.mmu_pte_list_desc_cache.gfp_zero = __GFP_ZERO;
> +
>         vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
> +       vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
>
>         vcpu->arch.mmu = &vcpu->arch.root_mmu;
>         vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
> --
> 2.26.0
>