kvm: nVMX: Add support for fast unprotection of nested guest page tables

This is the same as commit 14727754 ("kvm: svm: Add support for
additional SVM NPF error codes", 2016-11-23), but for Intel processors.
In this case, the exit qualification field's bit 8 says whether the
EPT violation occurred while translating the guest's final physical
address or rather while translating the guest page tables.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -204,7 +204,6 @@ enum {
 #define PFERR_GUEST_PAGE_MASK (1ULL << PFERR_GUEST_PAGE_BIT)
 
 #define PFERR_NESTED_GUEST_PAGE (PFERR_GUEST_PAGE_MASK |	\
-				 PFERR_USER_MASK |		\
 				 PFERR_WRITE_MASK |		\
 				 PFERR_PRESENT_MASK)
 

arch/x86/kvm/mmu.c

@@ -4836,12 +4836,9 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
 	 * This can occur when using nested virtualization with nested
 	 * paging in both guests. If true, we simply unprotect the page
 	 * and resume the guest.
-	 *
-	 * Note: AMD only (since it supports the PFERR_GUEST_PAGE_MASK used
-	 *       in PFERR_NEXT_GUEST_PAGE)
 	 */
 	if (vcpu->arch.mmu.direct_map &&
-		error_code == PFERR_NESTED_GUEST_PAGE) {
+	    (error_code & PFERR_NESTED_GUEST_PAGE) == PFERR_NESTED_GUEST_PAGE) {
 		kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(cr2));
 		return 1;
 	}

arch/x86/kvm/vmx.c

@@ -6358,7 +6358,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification;
 	gpa_t gpa;
-	u32 error_code;
+	u64 error_code;
 
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 
@@ -6390,6 +6390,9 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 			EPT_VIOLATION_EXECUTABLE))
 		      ? PFERR_PRESENT_MASK : 0;
 
+	error_code |= (exit_qualification & 0x100) != 0 ?
+	       PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
+
 	vcpu->arch.gpa_available = true;
 	vcpu->arch.exit_qualification = exit_qualification;