Re: [PATCH v10 5/9] KVM: x86: Virtualize CR3.LAM_{U48,U57}

[Sean Christopherson]

On Wed, Jul 19, 2023, Binbin Wu wrote:
> Add support to allow guests to set two new CR3 non-address control bits for
> guests to enable the new Intel CPU feature Linear Address Masking (LAM) on user
> pointers.

Same feedback as the LAM_SUP patch.

> ---
>  arch/x86/kvm/cpuid.h   | 3 +++
>  arch/x86/kvm/mmu.h     | 8 ++++++++
>  arch/x86/kvm/mmu/mmu.c | 2 +-
>  arch/x86/kvm/vmx/vmx.c | 3 ++-
>  4 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 8b26d946f3e3..274f41d2250b 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -285,6 +285,9 @@ static __always_inline bool guest_can_use(struct kvm_vcpu *vcpu,
>  
>  static inline bool kvm_vcpu_is_legal_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
>  {
> +	if (guest_can_use(vcpu, X86_FEATURE_LAM))
> +		cr3 &= ~(X86_CR3_LAM_U48 | X86_CR3_LAM_U57);
> +
>  	return kvm_vcpu_is_legal_gpa(vcpu, cr3);
>  }
>  
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 92d5a1924fc1..e92395e6b876 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -144,6 +144,14 @@ static inline unsigned long kvm_get_active_pcid(struct kvm_vcpu *vcpu)
>  	return kvm_get_pcid(vcpu, kvm_read_cr3(vcpu));
>  }
>  
> +static inline unsigned long kvm_get_active_cr3_lam_bits(struct kvm_vcpu *vcpu)
> +{
> +	if (!guest_can_use(vcpu, X86_FEATURE_LAM))
> +		return 0;
> +
> +	return kvm_read_cr3(vcpu) & (X86_CR3_LAM_U48 | X86_CR3_LAM_U57);
> +}
> +
>  static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
>  {
>  	u64 root_hpa = vcpu->arch.mmu->root.hpa;
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index ec169f5c7dce..0285536346c1 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3819,7 +3819,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
>  	hpa_t root;
>  
>  	root_pgd = kvm_mmu_get_guest_pgd(vcpu, mmu);
> -	root_gfn = root_pgd >> PAGE_SHIFT;
> +	root_gfn = (root_pgd & __PT_BASE_ADDR_MASK) >> PAGE_SHIFT;

And as mentioned previously, this should be in the patch that adds __PT_BASE_ADDR_MASK.

>  	if (mmu_check_root(vcpu, root_gfn))
>  		return 1;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index a0d6ea87a2d0..bcee5dc3dd0b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3358,7 +3358,8 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>  			update_guest_cr3 = false;
>  		vmx_ept_load_pdptrs(vcpu);
>  	} else {
> -		guest_cr3 = root_hpa | kvm_get_active_pcid(vcpu);
> +		guest_cr3 = root_hpa | kvm_get_active_pcid(vcpu) |
> +		            kvm_get_active_cr3_lam_bits(vcpu);
>  	}
>  
>  	if (update_guest_cr3)
> -- 
> 2.25.1
>