linux-kernel - Re: [PATCH 22/22] kvm: mmu: Don't clear write flooding count for direct roots

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Date:   Sat, 26 Sep 2020 03:25:28 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH 22/22] kvm: mmu: Don't clear write flooding count for
 direct roots

On 25/09/20 23:23, Ben Gardon wrote:
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 42dde27decd75..c07831b0c73e1 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -124,6 +124,18 @@ static struct kvm_mmu_page *find_tdp_mmu_root_with_role(
>  	return NULL;
>  }
>  
> +hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
> +				    union kvm_mmu_page_role role)
> +{
> +	struct kvm_mmu_page *root;
> +
> +	root = find_tdp_mmu_root_with_role(kvm, role);
> +	if (root)
> +		return __pa(root->spt);
> +
> +	return INVALID_PAGE;
> +}
> +
>  static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
>  						   int level)
>  {
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index cc0b7241975aa..2395ffa71bb05 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -9,6 +9,8 @@ void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
>  void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
>  
>  bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
> +hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
> +				    union kvm_mmu_page_role role);
>  hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
>  void kvm_tdp_mmu_put_root_hpa(struct kvm *kvm, hpa_t root_hpa);
>  

Probably missing a piece since this code is not used and neither is the
new argument to is_root_usable.

I'm a bit confused by is_root_usable since there should be only one PGD
for the TDP MMU (the one for the root_mmu).

Paolo