Re: [PATCH v6 05/18] KVM: x86/mmu: Add an is_mirror member for union kvm_mmu_page_role

[Yan Zhao <yan.y.zhao@intel.com>]

On Sun, Dec 22, 2024 at 02:34:32PM -0500, Paolo Bonzini wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> Introduce a "is_mirror" member to the kvm_mmu_page_role union to identify
> SPTEs associated with the mirrored EPT.
> 
> The TDX module maintains the private half of the EPT mapped in the TD in
> its protected memory. KVM keeps a copy of the private GPAs in a mirrored
> EPT tree within host memory. This "is_mirror" attribute enables vCPUs to
> find and get the root page of mirrored EPT from the MMU root list for a
> guest TD. This also allows KVM MMU code to detect changes in mirrored EPT
> according to the "is_mirror" mmu page role and propagate the changes to
> the private EPT managed by TDX module.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Message-ID: <20240718211230.1492011-6-rick.p.edgecombe@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 3 ++-
>  arch/x86/kvm/mmu/mmu_internal.h | 5 +++++
>  arch/x86/kvm/mmu/spte.h         | 5 +++++
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5f020b097922..cae88f023caf 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -349,7 +349,8 @@ union kvm_mmu_page_role {
>  		unsigned ad_disabled:1;
>  		unsigned guest_mode:1;
>  		unsigned passthrough:1;
> -		unsigned :5;
> +		unsigned is_mirror:1;
> +		unsigned :4;
>  
>  		/*
>  		 * This is left at the top of the word so that

Sorry for not spotting it earlier.
We may still need to update the comment for kvm_mmu_page_role. e.g.,

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4b4976fa95ad..07adf7c875f8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -315,10 +315,11 @@ struct kvm_kernel_irq_routing_entry;
  * the number of unique SPs that can theoretically be created is 2^n, where n
  * is the number of bits that are used to compute the role.
  *
- * But, even though there are 19 bits in the mask below, not all combinations
+ * But, even though there are 20 bits in the mask below, not all combinations
  * of modes and flags are possible:
  *
- *   - invalid shadow pages are not accounted, so the bits are effectively 18
+ *   - invalid shadow pages are not accounted, mirror pages are not shadowed,
+ *     so the bits are effectively 18.
  *
  *   - quadrant will only be used if has_4_byte_gpte=1 (non-PAE paging);
  *     execonly and ad_disabled are only used for nested EPT which has



> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index d9425064ecc5..ff00341f26a2 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -157,6 +157,11 @@ static inline int kvm_mmu_page_as_id(struct kvm_mmu_page *sp)
>  	return kvm_mmu_role_as_id(sp->role);
>  }
>  
> +static inline bool is_mirror_sp(const struct kvm_mmu_page *sp)
> +{
> +	return sp->role.is_mirror;
> +}
> +
>  static inline void kvm_mmu_alloc_external_spt(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>  {
>  	/*
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index af10bc0380a3..59746854c0af 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -276,6 +276,11 @@ static inline struct kvm_mmu_page *root_to_sp(hpa_t root)
>  	return spte_to_child_sp(root);
>  }
>  
> +static inline bool is_mirror_sptep(tdp_ptep_t sptep)
> +{
> +	return is_mirror_sp(sptep_to_sp(rcu_dereference(sptep)));
> +}
> +
>  static inline bool is_mmio_spte(struct kvm *kvm, u64 spte)
>  {
>  	return (spte & shadow_mmio_mask) == kvm->arch.shadow_mmio_value &&
> -- 
> 2.43.5
> 
>