[PATCH v6 1/6] platform/x86/amd/hsmp: Serialize ACPI HSMP probe and remove with an rwsem

[Muralidhara M K]

Add hsmp_sock_rwsem and export it, then hold it for write across ACPI
probe, remove and init_acpi() so concurrent per-socket platform probes
cannot race the is_probed handshake or the one-time socket-array
allocation. Use lockdep_assert_held_write() in init_acpi() to catch
incorrect locking under lockdep.

An rw_semaphore is used rather than a plain mutex because an upcoming
change adds a read side so the lock-free data plane runs concurrently with
itself while probe/remove hold it for write to drain in-flight messages.
Introducing it as an rwsem now keeps the lock type stable across that
change.

Signed-off-by: Muralidhara M K <muralidhara.mk@xxxxxxx>
---
 drivers/platform/x86/amd/hsmp/acpi.c | 22 ++++++++++++++++++++++
 drivers/platform/x86/amd/hsmp/hsmp.c |  9 +++++++++
 drivers/platform/x86/amd/hsmp/hsmp.h |  7 +++++++
 3 files changed, 38 insertions(+)

diff --git a/drivers/platform/x86/amd/hsmp/acpi.c b/drivers/platform/x86/amd/hsmp/acpi.c
index 72f68cef1297..a23797bd1dd5 100644
--- a/drivers/platform/x86/amd/hsmp/acpi.c
+++ b/drivers/platform/x86/amd/hsmp/acpi.c
@@ -15,12 +15,15 @@
 #include <linux/array_size.h>
 #include <linux/bits.h>
 #include <linux/bitfield.h>
+#include <linux/cleanup.h>
 #include <linux/device.h>
 #include <linux/dev_printk.h>
 #include <linux/ioport.h>
 #include <linux/kstrtox.h>
+#include <linux/lockdep.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
+#include <linux/rwsem.h>
 #include <linux/string.h>
 #include <linux/sysfs.h>
 #include <linux/topology.h>
@@ -482,11 +485,20 @@ static ssize_t hsmp_freq_limit_source_show(struct device *dev, struct device_att
 	return len;
 }
 
+/*
+ * Bring up one ACPI HSMP socket: parse its ACPI table, run the mailbox
+ * handshake and register its sysfs/hwmon interfaces.
+ *
+ * Called with hsmp_sock_rwsem held for write by hsmp_acpi_probe(), so the
+ * per-socket bring-up cannot race a concurrent probe or remove.
+ */
 static int init_acpi(struct device *dev)
 {
 	u16 sock_ind;
 	int ret;
 
+	lockdep_assert_held_write(&hsmp_sock_rwsem);
+
 	ret = hsmp_get_uid(dev, &sock_ind);
 	if (ret)
 		return ret;
@@ -607,6 +619,14 @@ static int hsmp_acpi_probe(struct platform_device *pdev)
 	if (!hsmp_pdev)
 		return -ENOMEM;
 
+	/*
+	 * Multiple ACPI socket devices probe in parallel, but the is_probed
+	 * handshake and the one-time socket-array allocation below must run
+	 * exactly once.  Serialize the whole bring-up against concurrent
+	 * probe/remove by holding the socket rwsem for write.
+	 */
+	guard(rwsem_write)(&hsmp_sock_rwsem);
+
 	if (!hsmp_pdev->is_probed) {
 		hsmp_pdev->num_sockets = topology_max_packages();
 		if (!hsmp_pdev->num_sockets) {
@@ -642,6 +662,8 @@ static int hsmp_acpi_probe(struct platform_device *pdev)
 
 static void hsmp_acpi_remove(struct platform_device *pdev)
 {
+	guard(rwsem_write)(&hsmp_sock_rwsem);
+
 	/*
 	 * We register only one misc_device even on multi-socket system.
 	 * So, deregister should happen only once.
diff --git a/drivers/platform/x86/amd/hsmp/hsmp.c b/drivers/platform/x86/amd/hsmp/hsmp.c
index 1a87931136fd..e9c17698983c 100644
--- a/drivers/platform/x86/amd/hsmp/hsmp.c
+++ b/drivers/platform/x86/amd/hsmp/hsmp.c
@@ -12,6 +12,7 @@
 #include <linux/acpi.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/rwsem.h>
 #include <linux/semaphore.h>
 #include <linux/sysfs.h>
 
@@ -40,6 +41,14 @@
 
 static struct hsmp_plat_device hsmp_pdev;
 
+/*
+ * Serializes AMD HSMP socket bring-up and teardown: ACPI probe and remove take
+ * it for write so concurrent per-socket probes cannot race the is_probed
+ * handshake or the one-time socket-array allocation.
+ */
+DECLARE_RWSEM(hsmp_sock_rwsem);
+EXPORT_SYMBOL_NS_GPL(hsmp_sock_rwsem, "AMD_HSMP");
+
 /*
  * Send a message to the HSMP port via PCI-e config space registers
  * or by writing to MMIO space.
diff --git a/drivers/platform/x86/amd/hsmp/hsmp.h b/drivers/platform/x86/amd/hsmp/hsmp.h
index 0509a442eaae..129200d0cf81 100644
--- a/drivers/platform/x86/amd/hsmp/hsmp.h
+++ b/drivers/platform/x86/amd/hsmp/hsmp.h
@@ -16,6 +16,7 @@
 #include <linux/kconfig.h>
 #include <linux/miscdevice.h>
 #include <linux/pci.h>
+#include <linux/rwsem.h>
 #include <linux/semaphore.h>
 #include <linux/sysfs.h>
 
@@ -71,4 +72,10 @@ int hsmp_create_sensor(struct device *dev, u16 sock_ind);
 static inline int hsmp_create_sensor(struct device *dev, u16 sock_ind) { return 0; }
 #endif
 int hsmp_msg_get_nargs(u16 sock_ind, u32 msg_id, u32 *data, u8 num_args);
+
+/*
+ * Serializes HSMP socket bring-up and teardown. ACPI probe and remove take it
+ * for write.
+ */
+extern struct rw_semaphore hsmp_sock_rwsem;
 #endif /* HSMP_H */
-- 
2.34.1