linux-kernel - Re: [PATCH v2 11/18] KVM: x86/mmu: Always use current mmu's role when loading new PGD

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Date:   Wed, 23 Feb 2022 18:23:28 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com
Subject: Re: [PATCH v2 11/18] KVM: x86/mmu: Always use current mmu's role
 when loading new PGD

On Thu, 2022-02-17 at 16:03 -0500, Paolo Bonzini wrote:
> Since the guest PGD is now loaded after the MMU has been set up
> completely, the desired role for a cache hit is simply the current
> mmu_role.  There is no need to compute it again, so __kvm_mmu_new_pgd
> can be folded in kvm_mmu_new_pgd.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 29 ++++-------------------------
>  1 file changed, 4 insertions(+), 25 deletions(-)

https://www.monkeyuser.com/2020/levels-of-satisfaction/ ;-)

> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 906a9244ad28..b01160716c6a 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -190,8 +190,6 @@ struct kmem_cache *mmu_page_header_cache;
>  static struct percpu_counter kvm_total_used_mmu_pages;
>  
>  static void mmu_spte_set(u64 *sptep, u64 spte);
> -static union kvm_mmu_page_role
> -kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu);
>  
>  struct kvm_mmu_role_regs {
>  	const unsigned long cr0;
> @@ -4191,10 +4189,10 @@ static bool fast_pgd_switch(struct kvm *kvm, struct kvm_mmu *mmu,
>  		return cached_root_find_without_current(kvm, mmu, new_pgd, new_role);
>  }
>  
> -static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd,
> -			      union kvm_mmu_page_role new_role)
> +void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd)
>  {
>  	struct kvm_mmu *mmu = vcpu->arch.mmu;
> +	union kvm_mmu_page_role new_role = mmu->mmu_role.base;
>  
>  	if (!fast_pgd_switch(vcpu->kvm, mmu, new_pgd, new_role)) {
>  		/* kvm_mmu_ensure_valid_pgd will set up a new root.  */
> @@ -4230,11 +4228,6 @@ static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd,
>  		__clear_sp_write_flooding_count(
>  				to_shadow_page(vcpu->arch.mmu->root.hpa));
>  }
> -
> -void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd)
> -{
> -	__kvm_mmu_new_pgd(vcpu, new_pgd, kvm_mmu_calc_root_page_role(vcpu));
> -}
>  EXPORT_SYMBOL_GPL(kvm_mmu_new_pgd);
>  
>  static unsigned long get_cr3(struct kvm_vcpu *vcpu)
> @@ -4904,7 +4897,7 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
>  	new_role = kvm_calc_shadow_npt_root_page_role(vcpu, &regs);
>  
>  	shadow_mmu_init_context(vcpu, context, &regs, new_role);
> -	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base);
> +	kvm_mmu_new_pgd(vcpu, nested_cr3);
>  }
>  EXPORT_SYMBOL_GPL(kvm_init_shadow_npt_mmu);
>  
> @@ -4960,7 +4953,7 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
>  		reset_ept_shadow_zero_bits_mask(context, execonly);
>  	}
>  
> -	__kvm_mmu_new_pgd(vcpu, new_eptp, new_role.base);
> +	kvm_mmu_new_pgd(vcpu, new_eptp);
>  }
>  EXPORT_SYMBOL_GPL(kvm_init_shadow_ept_mmu);
>  
> @@ -5045,20 +5038,6 @@ void kvm_init_mmu(struct kvm_vcpu *vcpu)
>  }
>  EXPORT_SYMBOL_GPL(kvm_init_mmu);
>  
> -static union kvm_mmu_page_role
> -kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu)
> -{
> -	struct kvm_mmu_role_regs regs = vcpu_to_role_regs(vcpu);
> -	union kvm_mmu_role role;
> -
> -	if (tdp_enabled)
> -		role = kvm_calc_tdp_mmu_root_page_role(vcpu, &regs, true);
> -	else
> -		role = kvm_calc_shadow_mmu_root_page_role(vcpu, &regs, true);
> -
> -	return role.base;
> -}
> -
>  void kvm_mmu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  {
>  	/*

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky