powerpc/kvm: Fix kvm_use_magic_page

stable inclusion
from stable-v5.10.110
commit e1a58498ef91f5713b8a0c41a8e09d5a640d8b7f
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e1a58498ef91f5713b8a0c41a8e09d5a640d8b7f

--------------------------------

commit 0c8eb288 upstream.

When switching from __get_user to fault_in_pages_readable, commit
9f9eae5c broke kvm_use_magic_page: like __get_user,
fault_in_pages_readable returns 0 on success.

Fixes: 9f9eae5c ("powerpc/kvm: Prefer fault_in_pages_readable function")
Cc: stable@vger.kernel.org # v4.18+
Signed-off-by: NAndreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/powerpc/kernel/kvm.c

@@ -669,7 +669,7 @@ static void __init kvm_use_magic_page(void)
 	on_each_cpu(kvm_map_magic_page, &features, 1);
 
 	/* Quick self-test to see if the mapping works */
-	if (!fault_in_pages_readable((const char *)KVM_MAGIC_PAGE, sizeof(u32))) {
+	if (fault_in_pages_readable((const char *)KVM_MAGIC_PAGE, sizeof(u32))) {
 		kvm_patching_worked = false;
 		return;
 	}