diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 3d9b87a9727a..dcbc9cf5581d 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -19,6 +19,7 @@
 #include <linux/platform_device.h>
 #include <linux/printk.h>
 #include <linux/srcu.h>
+#include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
@@ -740,6 +741,7 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 	if (err)
 		return ERR_PTR(err);
 
+	mpam_mon_sel_lock_init(msc);
 	msc->id = pdev->id;
 	msc->pdev = pdev;
 	INIT_LIST_HEAD_RCU(&msc->all_msc_list);
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 768a58a3ab27..97f02cf92d7a 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -10,6 +10,7 @@
 #include <linux/llist.h>
 #include <linux/mutex.h>
 #include <linux/srcu.h>
+#include <linux/spinlock.h>
 #include <linux/types.h>
 
 #define MPAM_MSC_MAX_NUM_RIS	16
@@ -65,12 +66,52 @@ struct mpam_msc {
 	 */
 	struct mutex		part_sel_lock;
 
+	/*
+	 * mon_sel_lock protects access to the MSC hardware registers that are
+	 * affected by MPAMCFG_MON_SEL, and the mbwu_state.
+	 * Access to mon_sel is needed from both process and interrupt contexts,
+	 * but is complicated by firmware-backed platforms that can't make any
+	 * access unless they can sleep.
+	 * Always use the mpam_mon_sel_lock() helpers.
+	 * Accesses to mon_sel need to be able to fail if they occur in the wrong
+	 * context.
+	 * If needed, take msc->probe_lock first.
+	 */
+	raw_spinlock_t		_mon_sel_lock;
+	unsigned long		_mon_sel_flags;
+
 	void __iomem		*mapped_hwpage;
 	size_t			mapped_hwpage_sz;
 
 	struct mpam_garbage	garbage;
 };
 
+/* Returning false here means accesses to mon_sel must fail and report an error. */
+static inline bool __must_check mpam_mon_sel_lock(struct mpam_msc *msc)
+{
+	/* Locking will require updating to support a firmware backed interface */
+	if (WARN_ON_ONCE(msc->iface != MPAM_IFACE_MMIO))
+		return false;
+
+	raw_spin_lock_irqsave(&msc->_mon_sel_lock, msc->_mon_sel_flags);
+	return true;
+}
+
+static inline void mpam_mon_sel_unlock(struct mpam_msc *msc)
+{
+	raw_spin_unlock_irqrestore(&msc->_mon_sel_lock, msc->_mon_sel_flags);
+}
+
+static inline void mpam_mon_sel_lock_held(struct mpam_msc *msc)
+{
+	lockdep_assert_held_once(&msc->_mon_sel_lock);
+}
+
+static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc)
+{
+	raw_spin_lock_init(&msc->_mon_sel_lock);
+}
+
 struct mpam_class {
 	/* mpam_components in this class */
 	struct list_head	components;