KVM: x86/mmu: Add an is_mirror member for union kvm_mmu_page_role

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>

Author: yamahata

arch/x86/include/asm/kvm_host.h

@@ -313,10 +313,11 @@ 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
@@ -349,7 +350,8 @@ 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

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)
 {
 	/*

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 &&