linux-kernel - Re: [PATCH v2 11/25] KVM: x86/mmu: remove kvm_calc_shadow_root_page_role

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Message-ID: <YieW+PZarPdsSnO7@google.com>
Date:   Tue, 8 Mar 2022 17:48:40 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        dmatlack@...gle.com
Subject: Re: [PATCH v2 11/25] KVM: x86/mmu: remove
 kvm_calc_shadow_root_page_role_common

On Mon, Feb 21, 2022, Paolo Bonzini wrote:
> kvm_calc_shadow_root_page_role_common is the same as
> kvm_calc_cpu_mode except for the level, which is overwritten
> afterwards in kvm_calc_shadow_mmu_root_page_role
> and kvm_calc_shadow_npt_root_page_role.
> 
> role.base.direct is already set correctly for the CPU mode,
> and CR0.PG=1 is required for VMRUN so it will also be
> correct for nested NPT.

Bzzzt, this is wrong, the nested NPT MMU is indirect but will be computed as direct.

> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 21 ++-------------------
>  1 file changed, 2 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 3ffa6f2bf991..31874fad12fb 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4796,27 +4796,11 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu,
>  	reset_tdp_shadow_zero_bits_mask(context);
>  }
>  
> -static union kvm_mmu_role
> -kvm_calc_shadow_root_page_role_common(struct kvm_vcpu *vcpu,
> -				      const struct kvm_mmu_role_regs *regs)
> -{
> -	union kvm_mmu_role role = kvm_calc_mmu_role_common(vcpu, regs);
> -
> -	role.base.smep_andnot_wp = role.ext.cr4_smep && !____is_cr0_wp(regs);
> -	role.base.smap_andnot_wp = role.ext.cr4_smap && !____is_cr0_wp(regs);
> -	role.base.has_4_byte_gpte = ____is_cr0_pg(regs) && !____is_cr4_pae(regs);
> -
> -	return role;
> -}
> -
>  static union kvm_mmu_role
>  kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
>  				   const struct kvm_mmu_role_regs *regs)
>  {
> -	union kvm_mmu_role role =
> -		kvm_calc_shadow_root_page_role_common(vcpu, regs);
> -
> -	role.base.direct = !____is_cr0_pg(regs);
> +	union kvm_mmu_role role = kvm_calc_cpu_mode(vcpu, regs);
>  
>  	if (!____is_efer_lma(regs))
>  		role.base.level = PT32E_ROOT_LEVEL;
> @@ -4869,9 +4853,8 @@ kvm_calc_shadow_npt_root_page_role(struct kvm_vcpu *vcpu,
>  				   const struct kvm_mmu_role_regs *regs)
>  {
>  	union kvm_mmu_role role =
> -		kvm_calc_shadow_root_page_role_common(vcpu, regs);
> +               kvm_calc_cpu_mode(vcpu, regs);

No need to split this line with the less verbose name.

>  
> -	role.base.direct = false;

As above, this line needs to stay.

>  	role.base.level = kvm_mmu_get_tdp_level(vcpu);
>  
>  	return role;
> -- 
> 2.31.1
> 
>