linux-kernel - Re: [PATCH 18/54] KVM: x86/mmu: Move nested NPT reserved bit calculation into MMU proper

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Date:   Wed, 23 Jun 2021 19:13:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH 18/54] KVM: x86/mmu: Move nested NPT reserved bit
 calculation into MMU proper

On 22/06/21 19:57, Sean Christopherson wrote:
> Move nested NPT's invocation of reset_shadow_zero_bits_mask() into the
> MMU proper and unexport said function.  Aside from dropping an export,
> this is a baby step toward eliminating the call entirely by fixing the
> shadow_root_level confusion.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Extra points for adding a comment about why the heck it's there.

Paolo

> ---
>   arch/x86/kvm/mmu.h        |  3 ---
>   arch/x86/kvm/mmu/mmu.c    | 11 ++++++++---
>   arch/x86/kvm/svm/nested.c |  1 -
>   3 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 4e926f4935b0..62844bacd13f 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -68,9 +68,6 @@ static __always_inline u64 rsvd_bits(int s, int e)
>   void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask);
>   void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only);
>   
> -void
> -reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
> -
>   void kvm_init_mmu(struct kvm_vcpu *vcpu);
>   void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
>   			     unsigned long cr4, u64 efer, gpa_t nested_cr3);
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 02c54426e7a2..5a46a87b23b0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4212,8 +4212,8 @@ static inline u64 reserved_hpa_bits(void)
>    * table in guest or amd nested guest, its mmu features completely
>    * follow the features in guest.
>    */
> -void
> -reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
> +static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,
> +					struct kvm_mmu *context)
>   {
>   	/*
>   	 * KVM uses NX when TDP is disabled to handle a variety of scenarios,
> @@ -4247,7 +4247,6 @@ reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
>   	}
>   
>   }
> -EXPORT_SYMBOL_GPL(reset_shadow_zero_bits_mask);
>   
>   static inline bool boot_cpu_is_amd(void)
>   {
> @@ -4714,6 +4713,12 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
>   		 */
>   		context->shadow_root_level = new_role.base.level;
>   	}
> +
> +	/*
> +	 * Redo the shadow bits, the reset done by shadow_mmu_init_context()
> +	 * (above) may use the wrong shadow_root_level.
> +	 */
> +	reset_shadow_zero_bits_mask(vcpu, context);
>   }
>   EXPORT_SYMBOL_GPL(kvm_init_shadow_npt_mmu);
>   
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 33b2f9337e26..927e545591c3 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -110,7 +110,6 @@ static void nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
>   	vcpu->arch.mmu->get_guest_pgd     = nested_svm_get_tdp_cr3;
>   	vcpu->arch.mmu->get_pdptr         = nested_svm_get_tdp_pdptr;
>   	vcpu->arch.mmu->inject_page_fault = nested_svm_inject_npf_exit;
> -	reset_shadow_zero_bits_mask(vcpu, vcpu->arch.mmu);
>   	vcpu->arch.walk_mmu              = &vcpu->arch.nested_mmu;
>   }
>   
>