KVM: x86/mmu: allow kvm_faultin_pfn to return page fault handling code

This will allow it to return RET_PF_EMULATE for APIC mmio
emulation.

This code is based on a patch from Sean Christopherson:
https://lkml.org/lkml/2021/7/19/2970Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210810205251.424103-7-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -3886,7 +3886,7 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 
 static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 			 gpa_t cr2_or_gpa, kvm_pfn_t *pfn, hva_t *hva,
-			 bool write, bool *writable)
+			 bool write, bool *writable, int *r)
 {
 	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 	bool async;
@@ -3897,7 +3897,7 @@ static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 	 * be zapped before KVM inserts a new MMIO SPTE for the gfn.
 	 */
 	if (slot && (slot->flags & KVM_MEMSLOT_INVALID))
-		return true;
+		goto out_retry;
 
 	/* Don't expose private memslots to L2. */
 	if (is_guest_mode(vcpu) && !kvm_is_visible_memslot(slot)) {
@@ -3917,14 +3917,17 @@ static bool kvm_faultin_pfn(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
 		if (kvm_find_async_pf_gfn(vcpu, gfn)) {
 			trace_kvm_async_pf_doublefault(cr2_or_gpa, gfn);
 			kvm_make_request(KVM_REQ_APF_HALT, vcpu);
-			return true;
+			goto out_retry;
 		} else if (kvm_arch_setup_async_pf(vcpu, cr2_or_gpa, gfn))
-			return true;
+			goto out_retry;
 	}
 
 	*pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL,
 				    write, writable, hva);
-	return false;
+
+out_retry:
+	*r = RET_PF_RETRY;
+	return true;
 }
 
 static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
@@ -3955,8 +3958,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	smp_rmb();
 
 	if (kvm_faultin_pfn(vcpu, prefault, gfn, gpa, &pfn, &hva,
-			 write, &map_writable))
-		return RET_PF_RETRY;
+			 write, &map_writable, &r))
+		return r;
 
 	if (handle_abnormal_pfn(vcpu, is_tdp ? 0 : gpa, gfn, pfn, ACC_ALL, &r))
 		return r;

arch/x86/kvm/mmu/paging_tmpl.h

@@ -882,8 +882,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 	smp_rmb();
 
 	if (kvm_faultin_pfn(vcpu, prefault, walker.gfn, addr, &pfn, &hva,
-			 write_fault, &map_writable))
-		return RET_PF_RETRY;
+			 write_fault, &map_writable, &r))
+		return r;
 
 	if (handle_abnormal_pfn(vcpu, addr, walker.gfn, pfn, walker.pte_access, &r))
 		return r;