KVM: arm64: Move S1PTW S2 fault logic out of io_mem_abort()

To allow for re-injection of stage-2 faults on stage-1 page-table walks
due to either a missing or read-only memslot, move the triage logic out
of io_mem_abort() and into kvm_handle_guest_abort(), where these aborts
can be handled before anything else.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20200729102821.23392-5-will@kernel.org

arch/arm64/kvm/mmio.c

@@ -145,12 +145,6 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		return -ENOSYS;
 	}
 
-	/* Page table accesses IO mem: tell guest to fix its TTBR */
-	if (kvm_vcpu_dabt_iss1tw(vcpu)) {
-		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
-		return 1;
-	}
-
 	/*
 	 * Prepare MMIO operation. First decode the syndrome data we get
 	 * from the CPU. Then try if some in-kernel emulation feels

arch/arm64/kvm/mmu.c

@@ -2105,12 +2105,23 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
 	write_fault = kvm_is_write_fault(vcpu);
 	if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
+		/*
+		 * The guest has put either its instructions or its page-tables
+		 * somewhere it shouldn't have. Userspace won't be able to do
+		 * anything about this (there's no syndrome for a start), so
+		 * re-inject the abort back into the guest.
+		 */
 		if (is_iabt) {
-			/* Prefetch Abort on I/O address */
 			ret = -ENOEXEC;
 			goto out;
 		}
 
+		if (kvm_vcpu_dabt_iss1tw(vcpu)) {
+			kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
+			ret = 1;
+			goto out_unlock;
+		}
+
 		/*
 		 * Check for a cache maintenance operation. Since we
 		 * ended-up here, we know it is outside of any memory