[PATCH v4 3/4] KVM: x86/mmu: Move slot checks from __kvm_faultin_pfn() to kvm_faultin_pfn()

[Sean Christopherson <seanjc@google.com>]

Move the checks related to the validity of an access to a memslot from the
inner __kvm_faultin_pfn() to its sole caller, kvm_faultin_pfn().  This
allows emulating accesses to the APIC access page, which don't need to
resolve a pfn, even if there is a relevant in-progress mmu_notifier
invalidation.  Ditto for accesses to KVM internal memslots from L2, which
KVM also treats as emulated MMIO.

More importantly, this will allow for future cleanup by having the
"no memslot" case bail from kvm_faultin_pfn() very early on.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 62 ++++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 50bfaa53f3f2..505fc7eef533 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4333,33 +4333,6 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	struct kvm_memory_slot *slot = fault->slot;
 	bool async;
 
-	/*
-	 * 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
-	 * be zapped before KVM inserts a new MMIO SPTE for the gfn.
-	 */
-	if (slot && (slot->flags & KVM_MEMSLOT_INVALID))
-		return RET_PF_RETRY;
-
-	if (!kvm_is_visible_memslot(slot)) {
-		/* Don't expose private memslots to L2. */
-		if (is_guest_mode(vcpu)) {
-			fault->slot = NULL;
-			fault->pfn = KVM_PFN_NOSLOT;
-			fault->map_writable = false;
-			return RET_PF_CONTINUE;
-		}
-		/*
-		 * If the APIC access page exists but is disabled, go directly
-		 * to emulation without caching the MMIO access or creating a
-		 * MMIO SPTE.  That way the cache doesn't need to be purged
-		 * when the AVIC is re-enabled.
-		 */
-		if (slot && slot->id == APIC_ACCESS_PAGE_PRIVATE_MEMSLOT &&
-		    !kvm_apicv_activated(vcpu->kvm))
-			return RET_PF_EMULATE;
-	}
-
 	if (fault->is_private)
 		return kvm_faultin_pfn_private(vcpu, fault);
 
@@ -4406,6 +4379,37 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	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
+	 * be zapped before KVM inserts a new MMIO SPTE for the gfn.
+	 */
+	if (slot->flags & KVM_MEMSLOT_INVALID)
+		return RET_PF_RETRY;
+
+	if (!kvm_is_visible_memslot(slot)) {
+		/* Don't expose KVM's internal memslots to L2. */
+		if (is_guest_mode(vcpu)) {
+			fault->slot = NULL;
+			fault->pfn = KVM_PFN_NOSLOT;
+			fault->map_writable = false;
+			return RET_PF_CONTINUE;
+		}
+
+		/*
+		 * If the APIC access page exists but is disabled, go directly
+		 * to emulation without caching the MMIO access or creating a
+		 * MMIO SPTE.  That way the cache doesn't need to be purged
+		 * when the AVIC is re-enabled.
+		 */
+		if (slot->id == APIC_ACCESS_PAGE_PRIVATE_MEMSLOT &&
+		    !kvm_apicv_activated(vcpu->kvm))
+			return RET_PF_EMULATE;
+	}
+
 	/*
 	 * Check for a relevant mmu_notifier invalidation event before getting
 	 * the pfn from the primary MMU, and before acquiring mmu_lock.
@@ -4427,10 +4431,10 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	 * *guaranteed* to need to retry, i.e. waiting until mmu_lock is held
 	 * to detect retry guarantees the worst case latency for the vCPU.
 	 */
-	if (!slot &&
-	    mmu_invalidate_retry_gfn_unsafe(vcpu->kvm, fault->mmu_seq, fault->gfn))
+	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;
-- 
2.43.0.687.g38aa6559b0-goog