[PATCH v9 09/10] firmware: arm_ffa: Introduce ffa-lend-pool

[Vincent Donnefort]

When memory is lent to the Secure world via FF-A, fatal CPU speculative
reads from Non-Secure can still occur as long as it retains a cacheable
mapping to that memory. Introduce the "arm,ffa-lend-pool"
reserved-memory CMA driver to unmap pages before lending
(ffa_prepare_lend()) and restore them upon reclaim
(ffa_lend_reclaimed()). Devices bind to the pool via the "memory-region"
DT property or via ffa_lend_pool_attach().

  reserved-memory {
      #address-cells = <0x2>;
      #size-cells = <0x2>;
      ranges;

      ffa_lend: ffa-lend-pool {
          compatible = "arm,ffa-lend-pool";
          reusable;
          ll-map;
          size = <0x0 0x4000000>;
      };
  };

Signed-off-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>

diff --git a/drivers/firmware/arm_ffa/Kconfig b/drivers/firmware/arm_ffa/Kconfig
index 5e3ae5cf82e8..66dbf74c37c3 100644
--- a/drivers/firmware/arm_ffa/Kconfig
+++ b/drivers/firmware/arm_ffa/Kconfig
@@ -19,3 +19,8 @@ config ARM_FFA_SMCCC
 	bool
 	default ARM_FFA_TRANSPORT
 	depends on ARM64 && HAVE_ARM_SMCCC_DISCOVERY
+
+config ARM_FFA_LEND_POOL
+	bool
+	default y
+	depends on ARM_FFA_TRANSPORT && CMA && OF_RESERVED_MEM
diff --git a/drivers/firmware/arm_ffa/Makefile b/drivers/firmware/arm_ffa/Makefile
index 168990a7e792..5ea3019c407b 100644
--- a/drivers/firmware/arm_ffa/Makefile
+++ b/drivers/firmware/arm_ffa/Makefile
@@ -6,3 +6,4 @@ ffa-core-objs := $(ffa-bus-y)
 ffa-module-objs := $(ffa-driver-y) $(ffa-transport-y)
 obj-$(CONFIG_ARM_FFA_TRANSPORT)  = ffa-core.o
 obj-$(CONFIG_ARM_FFA_TRANSPORT) += ffa-module.o
+obj-$(CONFIG_ARM_FFA_LEND_POOL) += lend_pool.o
diff --git a/drivers/firmware/arm_ffa/lend_pool.c b/drivers/firmware/arm_ffa/lend_pool.c
new file mode 100644
index 000000000000..67a36f5d5aa6
--- /dev/null
+++ b/drivers/firmware/arm_ffa/lend_pool.c
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Arm FF-A Reserved Memory CMA driver for Memory Lending
+ *
+ * Prevents CPU speculative reads to secure memory by unmapping it from the
+ * kernel direct map. This only works if the reserved-memory is mapped at the
+ * last-level ("ll-map;" or "rodata=full") or if all CPUs in the system support
+ * BBML3.
+ *
+ * Copyright (C) 2026 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
+ */
+
+#include <linux/arm_ffa.h>
+#include <linux/cleanup.h>
+#include <linux/cma.h>
+#include <linux/dma-map-ops.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/rcupdate.h>
+#include <linux/set_memory.h>
+#include <linux/xarray.h>
+
+static DEFINE_XARRAY(ffa_lend_devices);
+
+static bool ffa_lend_pool_contains(struct device *dev, phys_addr_t addr, size_t size)
+{
+	phys_addr_t base, end;
+
+	if (!dev)
+		return false;
+
+	guard(rcu)();
+
+	if (xa_load(&ffa_lend_devices, (unsigned long)dev) != dev)
+		return false;
+
+	if (WARN_ON_ONCE(!dev->cma_area))
+		return false;
+
+	base = cma_get_base(dev->cma_area);
+	end = base + cma_get_size(dev->cma_area);
+
+	return addr >= base && (addr + size) <= end;
+}
+
+/**
+ * ffa_prepare_lend() - Prepare a memory region to be lent in FF-A
+ * @dev:	Device attached to the lend pool
+ * @addr:	Physical start address of the memory region
+ * @size:	Size in bytes
+ *
+ * When memory is lent via FF-A, TrustZone transitions it to the secure state.
+ * As long as Arm CPUs retain a valid mapping to that now-secure memory, they
+ * can speculatively read it, which is fatal on some systems.
+ *
+ * ffa_prepare_lend() prevents this by unmapping the memory range from the
+ * kernel's direct map.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int ffa_prepare_lend(struct device *dev, phys_addr_t addr, size_t size)
+{
+	unsigned long nr_pages = size >> PAGE_SHIFT;
+	struct page *page;
+	unsigned long i;
+	int ret;
+
+	if (!ffa_lend_pool_contains(dev, addr, size))
+		return -ENODEV;
+
+	page = pfn_to_page(PHYS_PFN(addr));
+	for (i = 0; i < nr_pages; i++) {
+		ret = __set_direct_map_invalid_noflush(page + i);
+
+		if (ret) {
+			while (i--)
+				__set_direct_map_default_noflush(page + i);
+
+			return ret;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ffa_prepare_lend);
+
+/**
+ * ffa_lend_reclaimed() - Restore a reclaimed FF-A memory region
+ * @dev:	Device attached to the lend pool
+ * @addr:	Physical start address of the memory region
+ * @size:	Size in bytes
+ *
+ * Restores a memory range into the kernel's direct mapping. It must be called
+ * after a successful FF-A memory reclaim invocation.
+ */
+void ffa_lend_reclaimed(struct device *dev, phys_addr_t addr, size_t size)
+{
+	unsigned long nr_pages = size >> PAGE_SHIFT;
+	struct page *page;
+	unsigned long i;
+
+	if (!ffa_lend_pool_contains(dev, addr, size))
+		return;
+
+	page = pfn_to_page(PHYS_PFN(addr));
+	for (i = 0; i < nr_pages; i++)
+		__set_direct_map_default_noflush(page + i);
+}
+EXPORT_SYMBOL_GPL(ffa_lend_reclaimed);
+
+/**
+ * ffa_lend_pool_attach() - Attach a device to the FF-A lend pool
+ * @dev:	Device to attach
+ *
+ * FF-A devices are dynamically discovered and might not have an associated
+ * device tree node with a "memory-region" phandle. In that case, drivers must
+ * use this function to attach to the "arm,ffa-lend-pool" reserved memory
+ * region.
+ *
+ * Return: 0 on success, negative error code otherwise.
+ */
+int ffa_lend_pool_attach(struct device *dev)
+{
+	struct device_node *np;
+	struct reserved_mem *rmem;
+
+	np = of_find_compatible_node(NULL, NULL, "arm,ffa-lend-pool");
+	if (!np)
+		return -ENODEV;
+
+	rmem = of_reserved_mem_lookup(np);
+	of_node_put(np);
+	if (!rmem || !rmem->ops || !rmem->ops->device_init)
+		return -EINVAL;
+
+	return rmem->ops->device_init(rmem, dev);
+}
+EXPORT_SYMBOL_GPL(ffa_lend_pool_attach);
+
+/**
+ * ffa_lend_pool_detach() - Detach a device from the FF-A lend pool
+ * @dev:	Device to detach
+ *
+ * Releases the device from the "arm,ffa-lend-pool" reserved memory region.
+ */
+void ffa_lend_pool_detach(struct device *dev)
+{
+	struct device_node *np;
+	struct reserved_mem *rmem;
+
+	np = of_find_compatible_node(NULL, NULL, "arm,ffa-lend-pool");
+	if (!np)
+		return;
+
+	rmem = of_reserved_mem_lookup(np);
+	of_node_put(np);
+
+	if (rmem && rmem->ops && rmem->ops->device_release)
+		rmem->ops->device_release(rmem, dev);
+}
+EXPORT_SYMBOL_GPL(ffa_lend_pool_detach);
+
+static int __init ffa_lend_pool_setup(unsigned long node, struct reserved_mem *rmem)
+{
+	struct cma *cma;
+	int ret;
+
+	if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
+	    of_get_flat_dt_prop(node, "no-map", NULL)) {
+		pr_err("FF-A lend pool: node must be 'reusable' and not 'no-map'\n");
+		return -EINVAL;
+	}
+
+	if (!IS_ALIGNED(rmem->base | rmem->size, CMA_MIN_ALIGNMENT_BYTES)) {
+		pr_err("FF-A lend pool: incorrect alignment of CMA region\n");
+		return -EINVAL;
+	}
+
+	ret = cma_init_reserved_mem(rmem->base, rmem->size, 0, rmem->name, &cma);
+	if (ret) {
+		pr_err("FF-A lend pool: unable to setup CMA region (%d)\n", ret);
+		return ret;
+	}
+
+	rmem->priv = cma;
+
+	return 0;
+}
+
+static int ffa_lend_pool_device_init(struct reserved_mem *rmem, struct device *dev)
+{
+	int ret;
+
+	if (!can_set_direct_map_range(pfn_to_page(PHYS_PFN(rmem->base)), rmem->size / PAGE_SIZE)) {
+		pr_err("FF-A lend pool: reserved memory cannot be unmapped in direct map\n");
+		return -EINVAL;
+	}
+
+	dev->cma_area = rmem->priv;
+
+	ret = xa_err(xa_store(&ffa_lend_devices, (unsigned long)dev, dev, GFP_KERNEL));
+	if (ret)
+		dev->cma_area = NULL;
+
+	return ret;
+}
+
+static void ffa_lend_pool_device_release(struct reserved_mem *rmem, struct device *dev)
+{
+	xa_erase(&ffa_lend_devices, (unsigned long)dev);
+	dev->cma_area = NULL;
+}
+
+static const struct reserved_mem_ops ffa_lend_pool_ops = {
+	.node_init	= ffa_lend_pool_setup,
+	.device_init	= ffa_lend_pool_device_init,
+	.device_release = ffa_lend_pool_device_release,
+};
+RESERVEDMEM_OF_DECLARE(ffa_lend_pool, "arm,ffa-lend-pool", &ffa_lend_pool_ops);
diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
index e71d83ee0aef..fa3570f85ff7 100644
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -519,4 +519,25 @@ struct ffa_ops {
 	const struct ffa_notifier_ops *notifier_ops;
 };
 
+#if IS_ENABLED(CONFIG_ARM_FFA_LEND_POOL)
+int ffa_lend_pool_attach(struct device *dev);
+void ffa_lend_pool_detach(struct device *dev);
+int ffa_prepare_lend(struct device *dev, phys_addr_t paddr, size_t size);
+void ffa_lend_reclaimed(struct device *dev, phys_addr_t paddr, size_t size);
+#else
+static inline int ffa_lend_pool_attach(struct device *dev)
+{
+	return -ENODEV;
+}
+static inline void ffa_lend_pool_detach(struct device *dev)
+{
+}
+static inline int ffa_prepare_lend(struct device *dev, phys_addr_t paddr, size_t size)
+{
+	return -ENODEV;
+}
+static inline void ffa_lend_reclaimed(struct device *dev, phys_addr_t paddr, size_t size)
+{
+}
+#endif
 #endif /* _LINUX_ARM_FFA_H */
-- 
2.55.0.970.g62bdec98f9-goog