KVM: x86/mmu: Handle no-slot faults in kvm_faultin_pfn()

Handle faults on GFNs that do not have a backing memslot in
kvm_faultin_pfn() and drop handle_abnormal_pfn(). This eliminates
duplicate code in the various page fault handlers.

Opportunistically tweak the comment about handling gfn > host.MAXPHYADDR
to reflect that the effect of returning RET_PF_EMULATE at that point is
to avoid creating an MMIO SPTE for such GFNs.

No functional change intended.
Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220921173546.2674386-7-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -3218,28 +3218,32 @@ static int kvm_handle_error_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fa
 	return -EFAULT;
 }
 
-static int handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
-			       unsigned int access)
+static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
+				   struct kvm_page_fault *fault,
+				   unsigned int access)
 {
-	if (unlikely(!fault->slot)) {
-		gva_t gva = fault->is_tdp ? 0 : fault->addr;
+	gva_t gva = fault->is_tdp ? 0 : fault->addr;
 
-		vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
-				     access & shadow_mmio_access_mask);
-		/*
-		 * If MMIO caching is disabled, emulate immediately without
-		 * touching the shadow page tables as attempting to install an
-		 * MMIO SPTE will just be an expensive nop.  Do not cache MMIO
-		 * whose gfn is greater than host.MAXPHYADDR, any guest that
-		 * generates such gfns is running nested and is being tricked
-		 * by L0 userspace (you can observe gfn > L1.MAXPHYADDR if
-		 * and only if L1's MAXPHYADDR is inaccurate with respect to
-		 * the hardware's).
-		 */
-		if (unlikely(!enable_mmio_caching) ||
-		    unlikely(fault->gfn > kvm_mmu_max_gfn()))
-			return RET_PF_EMULATE;
-	}
+	vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
+			     access & shadow_mmio_access_mask);
+
+	/*
+	 * If MMIO caching is disabled, emulate immediately without
+	 * touching the shadow page tables as attempting to install an
+	 * MMIO SPTE will just be an expensive nop.
+	 */
+	if (unlikely(!enable_mmio_caching))
+		return RET_PF_EMULATE;
+
+	/*
+	 * Do not create an MMIO SPTE for a gfn greater than host.MAXPHYADDR,
+	 * any guest that generates such gfns is running nested and is being
+	 * tricked by L0 userspace (you can observe gfn > L1.MAXPHYADDR if and
+	 * only if L1's MAXPHYADDR is inaccurate with respect to the
+	 * hardware's).
+	 */
+	if (unlikely(fault->gfn > kvm_mmu_max_gfn()))
+		return RET_PF_EMULATE;
 
 	return RET_PF_CONTINUE;
 }
@@ -4248,7 +4252,8 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	return RET_PF_CONTINUE;
 }
 
-static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
+static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
+			   unsigned int access)
 {
 	int ret;
 
@@ -4262,6 +4267,9 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	if (unlikely(is_error_pfn(fault->pfn)))
 		return kvm_handle_error_pfn(vcpu, fault);
 
+	if (unlikely(!fault->slot))
+		return kvm_handle_noslot_fault(vcpu, fault, access);
+
 	return RET_PF_CONTINUE;
 }
 
@@ -4312,11 +4320,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	if (r)
 		return r;
 
-	r = kvm_faultin_pfn(vcpu, fault);
-	if (r != RET_PF_CONTINUE)
-		return r;
-
-	r = handle_abnormal_pfn(vcpu, fault, ACC_ALL);
+	r = kvm_faultin_pfn(vcpu, fault, ACC_ALL);
 	if (r != RET_PF_CONTINUE)
 		return r;
 

arch/x86/kvm/mmu/paging_tmpl.h

@@ -837,11 +837,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	else
 		fault->max_level = walker.level;
 
-	r = kvm_faultin_pfn(vcpu, fault);
-	if (r != RET_PF_CONTINUE)
-		return r;
-
-	r = handle_abnormal_pfn(vcpu, fault, walker.pte_access);
+	r = kvm_faultin_pfn(vcpu, fault, walker.pte_access);
 	if (r != RET_PF_CONTINUE)
 		return r;