[PATCH 1/2] x86/amd_node: fix integer divide by zero during init

[Steven Noonan]

On a Xen dom0 boot, this feature does not behave, and we end up
calculating:

    num_roots = 1
    num_nodes = 2
    roots_per_node = 0

This causes a divide-by-zero in the modulus inside the loop.

This change adds a couple of guards for invalid states where we might
get a divide-by-zero.

Signed-off-by: Steven Noonan <steven@xxxxxxxxxxxxxx>
Signed-off-by: Ariadne Conill <ariadne@ariadne.space>
CC: Yazen Ghannam <yazen.ghannam@xxxxxxx>
CC: x86@xxxxxxxxxxxxxxx
CC: stable@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/amd_node.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
index 3d0a4768d603c..cdc6ba224d4ad 100644
--- a/arch/x86/kernel/amd_node.c
+++ b/arch/x86/kernel/amd_node.c
@@ -282,6 +282,17 @@ static int __init amd_smn_init(void)
 		return -ENODEV;
 
 	num_nodes = amd_num_nodes();
+
+	if (!num_nodes)
+		return -ENODEV;
+
+	/* Possibly a virtualized environment (e.g. Xen) where we wi
ll get
+	 * roots_per_node=0 if the number of roots is fewer than number of
+	 * nodes
+	 */
+	if (num_roots < num_nodes)
+		return -ENODEV;
+
 	amd_roots = kcalloc(num_nodes, sizeof(*amd_roots), GFP_KERNEL);
 	if (!amd_roots)
 		return -ENOMEM;
-- 
2.51.2

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