arch/x86/kernel/amd_node.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * AMD Node helper functions and common defines
 *
 * Copyright (c) 2024, Advanced Micro Devices, Inc.
 * All Rights Reserved.
 *
 * Author: Yazen Ghannam <Yazen.Ghannam@amd.com>
 */

#include <linux/debugfs.h>
#include <asm/amd/node.h>

/*
 * AMD Nodes are a physical collection of I/O devices within an SoC. There can be one
 * or more nodes per package.
 *
 * The nodes are software-visible through PCI config space. All nodes are enumerated
 * on segment 0 bus 0. The device (slot) numbers range from 0x18 to 0x1F (maximum 8
 * nodes) with 0x18 corresponding to node 0, 0x19 to node 1, etc. Each node can be a
 * multi-function device.
 *
 * On legacy systems, these node devices represent integrated Northbridge functionality.
 * On Zen-based systems, these node devices represent Data Fabric functionality.
 *
 * See "Configuration Space Accesses" section in BKDGs or
 * "Processor x86 Core" -> "Configuration Space" section in PPRs.
 */
struct pci_dev *amd_node_get_func(u16 node, u8 func)
{
	if (node >= MAX_AMD_NUM_NODES)
		return NULL;

	return pci_get_domain_bus_and_slot(0, 0, PCI_DEVFN(AMD_NODE0_PCI_SLOT + node, func));
}

static struct pci_dev **amd_roots;

/* Protect the PCI config register pairs used for SMN. */
static DEFINE_MUTEX(smn_mutex);

#define SMN_INDEX_OFFSET	0x60
#define SMN_DATA_OFFSET		0x64

#define HSMP_INDEX_OFFSET	0xc4
#define HSMP_DATA_OFFSET	0xc8

/*
 * SMN accesses may fail in ways that are difficult to detect here in the called
 * functions amd_smn_read() and amd_smn_write(). Therefore, callers must do
 * their own checking based on what behavior they expect.
 *
 * For SMN reads, the returned value may be zero if the register is Read-as-Zero.
 * Or it may be a "PCI Error Response", e.g. all 0xFFs. The "PCI Error Response"
 * can be checked here, and a proper error code can be returned.
 *
 * But the Read-as-Zero response cannot be verified here. A value of 0 may be
 * correct in some cases, so callers must check that this correct is for the
 * register/fields they need.
 *
 * For SMN writes, success can be determined through a "write and read back"
 * However, this is not robust when done here.
 *
 * Possible issues:
 *
 * 1) Bits that are "Write-1-to-Clear". In this case, the read value should
 *    *not* match the write value.
 *
 * 2) Bits that are "Read-as-Zero"/"Writes-Ignored". This information cannot be
 *    known here.
 *
 * 3) Bits that are "Reserved / Set to 1". Ditto above.
 *
 * Callers of amd_smn_write() should do the "write and read back" check
 * themselves, if needed.
 *
 * For #1, they can see if their target bits got cleared.
 *
 * For #2 and #3, they can check if their target bits got set as intended.
 *
 * This matches what is done for RDMSR/WRMSR. As long as there's no #GP, then
 * the operation is considered a success, and the caller does their own
 * checking.
 */
static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, bool write)
{
	struct pci_dev *root;
	int err = -ENODEV;

	if (node >= amd_num_nodes())
		return err;

	/*
	 * Uninitialized amd_roots indicates pci_request_config_region_exclusive()
	 * didn't run or failed and thus the kernel cannot rely on having
	 * exclusive access to SMN registers so prevent that.
	 */
	if (!amd_roots)
		return err;

	root = amd_roots[node];
	if (!root)
		return err;

	guard(mutex)(&smn_mutex);

	err = pci_write_config_dword(root, i_off, address);
	if (err) {
		pr_warn("Error programming SMN address 0x%x.\n", address);
		return pcibios_err_to_errno(err);
	}

	err = (write ? pci_write_config_dword(root, d_off, *value)
		     : pci_read_config_dword(root, d_off, value));

	return pcibios_err_to_errno(err);
}

int __must_check amd_smn_read(u16 node, u32 address, u32 *value)
{
	int err = __amd_smn_rw(SMN_INDEX_OFFSET, SMN_DATA_OFFSET, node, address, value, false);

	if (PCI_POSSIBLE_ERROR(*value)) {
		err = -ENODEV;
		*value = 0;
	}

	return err;
}
EXPORT_SYMBOL_GPL(amd_smn_read);

int __must_check amd_smn_write(u16 node, u32 address, u32 value)
{
	return __amd_smn_rw(SMN_INDEX_OFFSET, SMN_DATA_OFFSET, node, address, &value, true);
}
EXPORT_SYMBOL_GPL(amd_smn_write);

int __must_check amd_smn_hsmp_rdwr(u16 node, u32 address, u32 *value, bool write)
{
	return __amd_smn_rw(HSMP_INDEX_OFFSET, HSMP_DATA_OFFSET, node, address, value, 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)
{
	u16 node;
	int ret;

	ret = kstrtou16_from_user(userbuf, count, 0, &node);
	if (ret)
		return ret;

	if (node >= amd_num_nodes())
		return -ENODEV;

	debug_node = node;
	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_CPU_OUT_OF_SPEC, 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 struct pci_dev *get_next_root(struct pci_dev *root)
{
	while ((root = pci_get_class(PCI_CLASS_BRIDGE_HOST << 8, root))) {
		/* Root device is Device 0 Function 0. */
		if (root->devfn)
			continue;

		if (root->vendor != PCI_VENDOR_ID_AMD &&
		    root->vendor != PCI_VENDOR_ID_HYGON)
			continue;

		break;
	}

	return root;
}

static bool enable_dfs;

static int __init amd_smn_enable_dfs(char *str)
{
	enable_dfs = true;
	return 1;
}
__setup("amd_smn_debugfs_enable", amd_smn_enable_dfs);

static int __init amd_smn_init(void)
{
	u16 count, num_roots, roots_per_node, node, num_nodes;
	struct pci_dev *root __free(pci_dev_put) = NULL;

	if (!cpu_feature_enabled(X86_FEATURE_ZEN))
		return 0;

	guard(mutex)(&smn_mutex);

	if (amd_roots)
		return 0;

	num_roots = 0;
	while ((root = get_next_root(root))) {
		pci_dbg(root, "Reserving PCI config space\n");

		/*
		 * There are a few SMN index/data pairs and other registers
		 * that shouldn't be accessed by user space. So reserve the
		 * entire PCI config space for simplicity rather than covering
		 * specific registers piecemeal.
		 */
		if (!pci_request_config_region_exclusive(root, 0, PCI_CFG_SPACE_SIZE, NULL)) {
			pci_err(root, "Failed to reserve config space\n");
			return -EEXIST;
		}

		num_roots++;
	}

	pr_debug("Found %d AMD root devices\n", num_roots);

	if (!num_roots)
		return -ENODEV;

	num_nodes = amd_num_nodes();
	amd_roots = kzalloc_objs(*amd_roots, num_nodes);
	if (!amd_roots)
		return -ENOMEM;

	roots_per_node = num_roots / num_nodes;
	if (!roots_per_node) {
		if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
			pr_warn(FW_BUG "Error detecting roots per node.\n");
		roots_per_node = 1;
	}

	count = 0;
	node = 0;
	while (node < num_nodes && (root = get_next_root(root))) {
		/* Use one root for each node and skip the rest. */
		if (count++ % roots_per_node)
			continue;

		pci_dbg(root, "is root for AMD node %u\n", node);
		amd_roots[node++] = pci_dev_get(root);
	}

	if (enable_dfs) {
		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;
}

fs_initcall(amd_smn_init);