KVM: arm64: Release pfn, i.e. put page, if copying MTE tags hits ZONE_DEVICE

Put the page reference acquired by gfn_to_pfn_prot() if
kvm_vm_ioctl_mte_copy_tags() runs into ZONE_DEVICE memory.  KVM's less-
than-stellar heuristics for dealing with pfn-mapped memory means that KVM
can get a page reference to ZONE_DEVICE memory.

Fixes: f0376edb1d ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240726235234.228822-2-seanjc@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/guest.c

@@ -1059,6 +1059,7 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
 		page = pfn_to_online_page(pfn);
 		if (!page) {
 			/* Reject ZONE_DEVICE memory */
+			kvm_release_pfn_clean(pfn);
 			ret = -EFAULT;
 			goto out;
 		}