KVM: VMX: Teach EPT violation helper about private mem

Teach EPT violation helper to check shared mask of a GPA to find out
whether the GPA is for private memory.

When EPT violation is triggered after TD accessing a private GPA, KVM will
exit to user space if the corresponding GFN's attribute is not private.
User space will then update GFN's attribute during its memory conversion
process. After that, TD will re-access the private GPA and trigger EPT
violation again. Only with GFN's attribute matches to private, KVM will
fault in private page, map it in mirrored TDP root, and propagate changes
to private EPT to resolve the EPT violation.

Relying on GFN's attribute tracking xarray to determine if a GFN is
private, as for KVM_X86_SW_PROTECTED_VM, may lead to endless EPT
violations.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Co-developed-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20241112073539.22056-1-yan.y.zhao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: rpedgeco

arch/x86/kvm/vmx/common.h

@@ -6,6 +6,12 @@
 
 #include "mmu.h"
 
+static inline bool vt_is_tdx_private_gpa(struct kvm *kvm, gpa_t gpa)
+{
+	/* For TDX the direct mask is the shared mask. */
+	return !kvm_is_addr_direct(kvm, gpa);
+}
+
 static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
 					     unsigned long exit_qualification)
 {
@@ -28,6 +34,9 @@ static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
 		error_code |= (exit_qualification & EPT_VIOLATION_GVA_TRANSLATED) ?
 			      PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
 
+	if (vt_is_tdx_private_gpa(vcpu->kvm, gpa))
+		error_code |= PFERR_PRIVATE_ACCESS;
+
 	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
 }