[PATCH 9/9] KVM: x86/mmu: Try to handle no-slot faults during kvm_faultin_pfn()

[David Matlack <dmatlack@google.com>]

Try to handle faults on GFNs that do not have a backing memslot during
kvm_faultin_pfn(), rather than relying on the caller to call
handle_abnormal_pfn() right after kvm_faultin_pfn(). This reduces all of
the page fault paths by eliminating duplicate code.

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>
---
 arch/x86/kvm/mmu/mmu.c         | 55 +++++++++++++++++-----------------
 arch/x86/kvm/mmu/paging_tmpl.h |  4 ---
 2 files changed, 27 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 47f4d1e81db1..741b92b1f004 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3154,28 +3154,32 @@ static int kvm_handle_error_pfn(struct kvm_page_fault *fault)
 	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;
 }
@@ -4181,6 +4185,9 @@ 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(fault);
 
+	if (unlikely(!fault->slot))
+		return kvm_handle_noslot_fault(vcpu, fault, ACC_ALL);
+
 	return RET_PF_CONTINUE;
 }
 
@@ -4239,10 +4246,6 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu,
 	if (r != RET_PF_CONTINUE)
 		return r;
 
-	r = handle_abnormal_pfn(vcpu, fault, ACC_ALL);
-	if (r != RET_PF_CONTINUE)
-		return r;
-
 	r = RET_PF_RETRY;
 	write_lock(&vcpu->kvm->mmu_lock);
 
@@ -4338,10 +4341,6 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	if (r != RET_PF_CONTINUE)
 		return r;
 
-	r = handle_abnormal_pfn(vcpu, fault, ACC_ALL);
-	if (r != RET_PF_CONTINUE)
-		return r;
-
 	r = RET_PF_RETRY;
 	read_lock(&vcpu->kvm->mmu_lock);
 
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index a199db4acecc..cf19227e842c 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -841,10 +841,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	if (r != RET_PF_CONTINUE)
 		return r;
 
-	r = handle_abnormal_pfn(vcpu, fault, walker.pte_access);
-	if (r != RET_PF_CONTINUE)
-		return r;
-
 	/*
 	 * Do not change pte_access if the pfn is a mmio page, otherwise
 	 * we will cache the incorrect access into mmio spte.
-- 
2.37.1.595.g718a3a8f04-goog