[PATCH] x86/platform/uv: Abort UV initialization when reduced nr_cpus requires it

[Steve Wahl]

When nr_cpus is set to a smaller number than actually present, there
is some node-to-socket mapping info we won't get access to in
build_socket_tables().  This could later result in using a -1 value
for some array indexing, and eventual kernel page faults.

To avoid this, if any unfilled table entries are found, print a
warning message, and resume initializing, acting as if this is not a
UV system.  UV features will be unavailable, but we will not cause
kernel dumps.

This is a condition we expect only in platform debugging situations,
not in day-to-day operation.

Fixes: 8a50c5851927 ("x86/platform/uv: UV support for sub-NUMA clustering")
Signed-off-by: Steve Wahl <steve.wahl@xxxxxxx>
---
 arch/x86/kernel/apic/x2apic_uv_x.c | 58 ++++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index d9384d5b4b8e..8cf3f61b0000 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -1567,11 +1567,13 @@ static void __init free_1_to_1_table(unsigned short **tp, char *tname, int min,
  * If the number of nodes is >1 per socket, socket to node table will
  * contain lowest node number on that socket.
  */
-static void __init build_socket_tables(void)
+static int __init build_socket_tables(void)
 {
 	struct uv_gam_range_entry *gre = uv_gre_table;
 	int nums, numn, nump;
-	int cpu, i, lnid;
+	int cpu, i, lnid, nid;
+	int sockid;
+	int rc = 0;
 	int minsock = _min_socket;
 	int maxsock = _max_socket;
 	int minpnode = _min_pnode;
@@ -1580,11 +1582,12 @@ static void __init build_socket_tables(void)
 	if (!gre) {
 		if (is_uv2_hub() || is_uv3_hub()) {
 			pr_info("UV: No UVsystab socket table, ignoring\n");
-			return;
+			return 0;
 		}
 		pr_err("UV: Error: UVsystab address translations not available!\n");
 		WARN_ON_ONCE(!gre);
-		return;
+		rc = -EINVAL;
+		goto err_free_tables;
 	}
 
 	numn = num_possible_nodes();
@@ -1596,10 +1599,8 @@ static void __init build_socket_tables(void)
 	    || (alloc_conv_table(nums, &_socket_to_pnode) < 0)
 	    || (alloc_conv_table(numn, &_node_to_socket) < 0)
 	    || (alloc_conv_table(nums, &_socket_to_node) < 0)) {
-		kfree(_pnode_to_socket);
-		kfree(_socket_to_pnode);
-		kfree(_node_to_socket);
-		return;
+		rc = -ENOMEM;
+		goto err_free_tables;
 	}
 
 	/* Fill in pnode/node/addr conversion list values: */
@@ -1623,9 +1624,9 @@ static void __init build_socket_tables(void)
 	/* Set socket -> node values: */
 	lnid = NUMA_NO_NODE;
 	for_each_possible_cpu(cpu) {
-		int nid = cpu_to_node(cpu);
-		int apicid, sockid;
+		int apicid;
 
+		nid = cpu_to_node(cpu);
 		if (lnid == nid)
 			continue;
 		lnid = nid;
@@ -1647,6 +1648,28 @@ static void __init build_socket_tables(void)
 			_socket_to_node[sockid - minsock]);
 	}
 
+	/*
+	 * If nr_cpus=<val> is used to reduce the cpu count below
+	 * what's actually present, the cpu loop above may not find
+	 * all the node to socket mappings needed to complete these
+	 * tables.  Abort UV init and act like a non-uv system if this
+	 * happens.
+	 */
+	for_each_node(nid) {
+		if (_node_to_socket[nid] == SOCK_EMPTY) {
+			pr_err("UV: Incomplete node table (nr_cpus too small?)\n");
+			rc = -EINVAL;
+			goto err_free_tables;
+		}
+	}
+	for (sockid = 0; sockid < nums; sockid++) {
+		if (_socket_to_node[sockid] == SOCK_EMPTY) {
+			pr_err("UV: Incomplete socket table (nr_cpus too small?)\n");
+			rc = -EINVAL;
+			goto err_free_tables;
+		}
+	}
+
 	/*
 	 * If e.g. socket id == pnode for all pnodes,
 	 *   system runs faster by removing corresponding conversion table.
@@ -1655,6 +1678,17 @@ static void __init build_socket_tables(void)
 	FREE_1_TO_1_TABLE(_node_to_socket, _min_socket, nums, numn);
 	FREE_1_TO_1_TABLE(_socket_to_pnode, _min_pnode, nums, nump);
 	FREE_1_TO_1_TABLE(_pnode_to_socket, _min_pnode, nums, nump);
+
+	return 0;
+
+ err_free_tables:
+	kfree(_pnode_to_socket);
+	kfree(_socket_to_pnode);
+	kfree(_node_to_socket);
+	kfree(_socket_to_node);
+	/* make is_uv_system() return false from now on */
+	uv_system_type = UV_NONE;
+	return rc;
 }
 
 /* Check which reboot to use */
@@ -1763,7 +1797,9 @@ static void __init uv_system_init_hub(void)
 		return;
 	}
 
-	build_socket_tables();
+	if (build_socket_tables() < 0)
+		return;
+
 	build_uv_gr_table();
 	set_block_size();
 	uv_init_hub_info(&hub_info);
-- 
2.26.2