[PATCH 16/16] x86/amd_smn: Add support for debugfs access to SMN registers

Yazen Ghannam
2024-10-23T17:22:30Z

From: Mario Limonciello <mario.limonciello@amd.com>

There are certain registers on AMD Zen systems that can only be
accessed through SMN.

Introduce a new interface that provides debugfs files for accessing SMN.
As this introduces the capability for userspace to manipulate the
hardware in unpredictable ways, taint the kernel when writing.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
---
arch/x86/kernel/amd_smn.c | 83 +++++++++++++++++++++++++++++++++++++++
1 file changed, 83 insertions(+)

diff --git a/arch/x86/kernel/amd_smn.c b/arch/x86/kernel/amd_smn.c
index aeebd63234f9..618d9a05f3d7 100644
--- a/arch/x86/kernel/amd_smn.c
+++ b/arch/x86/kernel/amd_smn.c
@@ -7,6 +7,7 @@
#define pr_fmt(fmt) "amd_smn: " fmt

#include <linux/pci.h>
+#include <linux/debugfs.h>

#include <asm/amd_smn.h>

@@ -113,6 +114,82 @@ int __must_check amd_smn_hsmp_rdwr(u16 node, u32 address, u32 *value, bool write
}
EXPORT_SYMBOL_GPL(amd_smn_hsmp_rdwr);

+static struct dentry *debugfs_dir;
+static u16 debug_node;
+static u32 debug_address;
+
+static ssize_t smn_node_write(struct file *file, const char __user *userbuf,
+ size_t count, loff_t *ppos)
+{
+ int ret;
+
+ ret = kstrtou16_from_user(userbuf, count, 0, &debug_node);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+static int smn_node_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "0x%08x\n", debug_node);
+ return 0;
+}
+
+static ssize_t smn_address_write(struct file *file, const char __user *userbuf,
+ size_t count, loff_t *ppos)
+{
+ int ret;
+
+ ret = kstrtouint_from_user(userbuf, count, 0, &debug_address);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+static int smn_address_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "0x%08x\n", debug_address);
+ return 0;
+}
+
+static int smn_value_show(struct seq_file *m, void *v)
+{
+ u32 val;
+ int ret;
+
+ ret = amd_smn_read(debug_node, debug_address, &val);
+ if (ret)
+ return ret;
+
+ seq_printf(m, "0x%08x\n", val);
+ return 0;
+}
+
+static ssize_t smn_value_write(struct file *file, const char __user *userbuf,
+ size_t count, loff_t *ppos)
+{
+ u32 val;
+ int ret;
+
+ ret = kstrtouint_from_user(userbuf, count, 0, &val);
+ if (ret)
+ return ret;
+
+ add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+
+ ret = amd_smn_write(debug_node, debug_address, val);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+DEFINE_SHOW_STORE_ATTRIBUTE(smn_node);
+DEFINE_SHOW_STORE_ATTRIBUTE(smn_address);
+DEFINE_SHOW_STORE_ATTRIBUTE(smn_value);
+
static int amd_cache_roots(void)
{
u16 node, num_nodes = amd_num_nodes();
@@ -180,6 +257,12 @@ static int __init amd_smn_init(void)
if (err)
return err;

+ debugfs_dir = debugfs_create_dir("amd_smn", arch_debugfs_dir);
+
+ debugfs_create_file("node", 0600, debugfs_dir, NULL, &smn_node_fops);
+ debugfs_create_file("address", 0600, debugfs_dir, NULL, &smn_address_fops);
+ debugfs_create_file("value", 0600, debugfs_dir, NULL, &smn_value_fops);
+
return 0;
}

--
2.43.0