KVM: arm/arm64: Change misleading use of is_error_pfn

When converting a gfn to a pfn, we call gfn_to_pfn_prot, which returns
various kinds of error values.  It turns out that is_error_pfn() only
returns true when the gfn was found in a memory slot and could somehow
not be used, but it does not return true if the gfn does not belong to
any memory slot.

Change use to is_error_noslot_pfn() which covers both cases.

Note: Since we already check for kvm_is_error_hva(hva) explicitly in the
caller of this function while holding the kvm->srcu lock protecting the
memory slots, this should never be a problem, but nevertheless this
change is warranted as it shows the intention of the code.
Reported-by: NJames Hogan <james.hogan@imgtec.com>
Signed-off-by: NChristoffer Dall <christoffer.dall@linaro.org>

arch/arm/kvm/mmu.c

@@ -1309,7 +1309,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	smp_rmb();
 
 	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
-	if (is_error_pfn(pfn))
+	if (is_error_noslot_pfn(pfn))
 		return -EFAULT;
 
 	if (kvm_is_device_pfn(pfn)) {