linux-kernel - Re: [PATCH 1/9] KVM: nSVM: Correctly set the shadow NPT root level in its MMU role

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Date:   Wed, 22 Jul 2020 19:02:08 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] KVM: nSVM: Correctly set the shadow NPT root level in its MMU role

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Move the initialization of shadow NPT MMU's shadow_root_level into
> kvm_init_shadow_npt_mmu() and explicitly set the level in the shadow NPT
> MMU's role to be the TDP level.  This ensures the role and MMU levels
> are synchronized and also initialized before __kvm_mmu_new_pgd(), which
> consumes the level when attempting a fast PGD switch.
>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Fixes: 9fa72119b24db ("kvm: x86: Introduce kvm_mmu_calc_root_page_role()")
> Fixes: a506fdd223426 ("KVM: nSVM: implement nested_svm_load_cr3() and use it for host->guest switch")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/mmu/mmu.c    | 3 +++
>  arch/x86/kvm/svm/nested.c | 1 -
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 77810ce66bdb4..678b6209dad50 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4963,6 +4963,9 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
>  	union kvm_mmu_role new_role =
>  		kvm_calc_shadow_mmu_root_page_role(vcpu, false);
>  
> +	new_role.base.level = vcpu->arch.tdp_level;
> +	context->shadow_root_level = new_role.base.level;
> +
>  	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base, false, false);
>  
>  	if (new_role.as_u64 != context->mmu_role.as_u64)
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 61378a3c2ce44..fb68467e60496 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -85,7 +85,6 @@ 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;
> -	vcpu->arch.mmu->shadow_root_level = vcpu->arch.tdp_level;
>  	reset_shadow_zero_bits_mask(vcpu, vcpu->arch.mmu);
>  	vcpu->arch.walk_mmu              = &vcpu->arch.nested_mmu;
>  }

FWIW,

Reviewed-and-tested-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly