[PATCH v4 4/4] KVM: x86/mmu: Handle no-slot faults at the beginning of kvm_faultin_pfn()

[Sean Christopherson]

Handle the "no memslot" case at the beginning of kvm_faultin_pfn(), just
after the private versus shared check, so that there's no need to
repeatedly query whether or not a slot exists.  This also makes it more
obvious that, except for private vs. shared attributes, the process of
faulting in a pfn simply doesn't apply to gfns without a slot.

Cc: David Matlack <dmatlack@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c          | 33 ++++++++++++++++++---------------
 arch/x86/kvm/mmu/mmu_internal.h |  5 ++++-
 2 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 505fc7eef533..7a2874756b3f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3278,6 +3278,14 @@ static int direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	return ret;
 }
 
+static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
+					      struct kvm_page_fault *fault)
+{
+	kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT,
+				      PAGE_SIZE, fault->write, fault->exec,
+				      fault->is_private);
+}
+
 static void kvm_send_hwpoison_signal(struct kvm_memory_slot *slot, gfn_t gfn)
 {
 	unsigned long hva = gfn_to_hva_memslot(slot, gfn);
@@ -3314,9 +3322,16 @@ static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
 {
 	gva_t gva = fault->is_tdp ? 0 : fault->addr;
 
+	if (fault->is_private) {
+		kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+		return -EFAULT;
+	}
+
 	vcpu_cache_mmio_info(vcpu, gva, fault->gfn,
 			     access & shadow_mmio_access_mask);
 
+	fault->pfn = KVM_PFN_NOSLOT;
+
 	/*
 	 * If MMIO caching is disabled, emulate immediately without
 	 * touching the shadow page tables as attempting to install an
@@ -4296,14 +4311,6 @@ static inline u8 kvm_max_level_for_order(int order)
 	return PG_LEVEL_4K;
 }
 
-static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
-					      struct kvm_page_fault *fault)
-{
-	kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT,
-				      PAGE_SIZE, fault->write, fault->exec,
-				      fault->is_private);
-}
-
 static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
 				   struct kvm_page_fault *fault)
 {
@@ -4376,12 +4383,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 		return -EFAULT;
 	}
 
+	if (unlikely(!slot))
+		return kvm_handle_noslot_fault(vcpu, fault, access);
+
 	fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
 	smp_rmb();
 
-	if (!slot)
-		goto faultin_pfn;
-
 	/*
 	 * Retry the page fault if the gfn hit a memslot that is being deleted
 	 * or moved.  This ensures any existing SPTEs for the old memslot will
@@ -4434,7 +4441,6 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	if (mmu_invalidate_retry_gfn_unsafe(vcpu->kvm, fault->mmu_seq, fault->gfn))
 		return RET_PF_RETRY;
 
-faultin_pfn:
 	ret = __kvm_faultin_pfn(vcpu, fault);
 	if (ret != RET_PF_CONTINUE)
 		return ret;
@@ -4442,9 +4448,6 @@ 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(!slot))
-		return kvm_handle_noslot_fault(vcpu, fault, access);
-
 	/*
 	 * Check again for a relevant mmu_notifier invalidation event purely to
 	 * avoid contending mmu_lock.  Most invalidations will be detected by
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 0669a8a668ca..bd7d07e6c697 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -235,7 +235,10 @@ struct kvm_page_fault {
 	/* The memslot containing gfn. May be NULL. */
 	struct kvm_memory_slot *slot;
 
-	/* Outputs of kvm_faultin_pfn.  */
+	/*
+	 * Outputs of kvm_faultin_pfn, guaranteed to be valid if and only if
+	 * slot is non-NULL.
+	 */
 	unsigned long mmu_seq;
 	kvm_pfn_t pfn;
 	hva_t hva;
-- 
2.43.0.687.g38aa6559b0-goog