[PATCH v2 5/8] firmware: arm_ffa: Introduce ffa-lend-pool

[Vincent Donnefort <vdonnefort@google.com>]

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;
          size = <0x0 0x4000000>;
      };
  };

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
---
 drivers/firmware/arm_ffa/Kconfig     |   5 +
 drivers/firmware/arm_ffa/Makefile    |   1 +
 drivers/firmware/arm_ffa/lend_pool.c | 261 +++++++++++++++++++++++++++
 include/linux/arm_ffa.h              |  23 +++
 4 files changed, 290 insertions(+)
 create mode 100644 drivers/firmware/arm_ffa/lend_pool.c

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..e4348f5c618b
--- /dev/null
+++ b/drivers/firmware/arm_ffa/lend_pool.c
@@ -0,0 +1,261 @@
+// 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 works if rodata=full or if all CPUs in the system
+ * support BBML3 or if a reserved-memory is declared for this driver
+ * "arm,ffa_lend_pool".
+ *
+ * Copyright (C) 2026 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#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/memblock.h>
+#include <linux/mm.h>
+#include <linux/of.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/rcupdate.h>
+#include <linux/suspend.h>
+#include <linux/set_memory.h>
+#include <linux/xarray.h>
+
+#include <linux/cacheflush.h>
+#include <asm/tlbflush.h>
+
+static DEFINE_XARRAY(ffa_lend_pool_devices);
+static atomic_t ffa_lend_pool_active;
+
+#define FFA_LEND_POOL_DISABLED	-1
+
+static bool ffa_lend_pool_can_set_direct_map(struct device *dev, struct page *page, u64 nr_pages)
+{
+	phys_addr_t addr, base, end;
+	size_t size;
+
+	if (can_set_direct_map())
+		return true;
+
+	if (!dev)
+		return false;
+
+	guard(rcu)();
+
+	if (xa_load(&ffa_lend_pool_devices, (unsigned long)dev) != dev)
+		return false;
+
+	if (WARN_ON_ONCE(!dev->cma_area))
+		return false;
+
+	addr = page_to_phys(page);
+	size = nr_pages << PAGE_SHIFT;
+	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
+ * @page:	First page of the memory region
+ * @nr_pages:	Number of pages
+ *
+ * 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, struct page *page, u64 nr_pages)
+{
+	struct page *p, *end;
+	unsigned long addr;
+	int ret;
+
+	if (!ffa_lend_pool_can_set_direct_map(dev, page, nr_pages))
+		return -ENODEV;
+
+	/* provides full ordering */
+	if (!atomic_add_unless(&ffa_lend_pool_active, 1, FFA_LEND_POOL_DISABLED))
+		return -EBUSY;
+
+	end = page + nr_pages;
+	for (p = page; p < end; p++)
+		flush_dcache_page(p);
+
+	ret = __set_direct_map_invalid_noflush(page, nr_pages);
+	if (ret) {
+		atomic_dec(&ffa_lend_pool_active);
+		return ret;
+	}
+
+	addr = (unsigned long)page_address(page);
+	flush_tlb_kernel_range(addr, addr + (nr_pages << PAGE_SHIFT));
+
+	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
+ * @page:	First page of the memory region
+ * @nr_pages:	Number of pages
+ *
+ * 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, struct page *page, u64 nr_pages)
+{
+	if (!ffa_lend_pool_can_set_direct_map(dev, page, nr_pages))
+		return;
+
+	__set_direct_map_default_noflush(page, nr_pages);
+
+	atomic_dec_return_release(&ffa_lend_pool_active);
+}
+EXPORT_SYMBOL_GPL(ffa_lend_reclaimed);
+
+static int ffa_lend_pool_pm_notify(struct notifier_block *nb, unsigned long mode, void *data)
+{
+	/* Prevent hibernation which would try to access lent memory */
+	switch (mode) {
+	case PM_HIBERNATION_PREPARE:
+		if (atomic_cmpxchg_acquire(&ffa_lend_pool_active, 0, FFA_LEND_POOL_DISABLED))
+			return notifier_from_errno(-EBUSY);
+		break;
+	case PM_POST_HIBERNATION:
+		atomic_set(&ffa_lend_pool_active, 0);
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ffa_lend_pool_pm_nb = {
+	.notifier_call	= ffa_lend_pool_pm_notify,
+};
+
+static const struct reserved_mem_ops ffa_lend_pool_ops;
+
+static struct reserved_mem *ffa_lend_pool_get_rmem(void)
+{
+	struct reserved_mem *rmem;
+	struct device_node *np;
+
+	np = of_find_compatible_node(NULL, NULL, "arm,ffa-lend-pool");
+	if (!np)
+		return NULL;
+
+	rmem = of_reserved_mem_lookup(np);
+	of_node_put(np);
+
+	if (WARN_ON_ONCE(rmem && rmem->ops != &ffa_lend_pool_ops))
+		return NULL;
+
+	return rmem;
+}
+
+/**
+ * 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 reserved_mem *rmem = ffa_lend_pool_get_rmem();
+
+	return rmem ? rmem->ops->device_init(rmem, dev) : -ENODEV;
+}
+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 reserved_mem *rmem = ffa_lend_pool_get_rmem();
+
+	if (rmem)
+		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;
+
+	/* Limited by ffa_lend_pool_active */
+	if (rmem->size / PAGE_SIZE > INT_MAX)
+		return -E2BIG;
+
+	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 = memblock_mark_ptemap(rmem->base, rmem->size);
+	if (ret)
+		return ret;
+
+	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);
+		memblock_clear_ptemap(rmem->base, rmem->size);
+		return ret;
+	}
+
+	register_pm_notifier(&ffa_lend_pool_pm_nb);
+	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_pool_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_pool_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..8608847931cc 100644
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -519,4 +519,27 @@ struct ffa_ops {
 	const struct ffa_notifier_ops *notifier_ops;
 };
 
+struct page;
+
+#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, struct page *page, u64 nr_pages);
+void ffa_lend_reclaimed(struct device *dev, struct page *page, u64 nr_pages);
+#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, struct page *page, u64 nr_pages)
+{
+	return -ENODEV;
+}
+static inline void ffa_lend_reclaimed(struct device *dev, struct page *page, u64 nr_pages)
+{
+}
+#endif
 #endif /* _LINUX_ARM_FFA_H */
-- 
2.55.0.1082.g2b9226bbc0-goog