firmware: arm_ffa: Add support for MEM_LEND

As part of the FF-A spec, an endpoint is allowed to transfer access of,
or lend, a memory region to one or more borrowers.

Extend the existing memory sharing implementation to support
FF-A MEM_LEND functionality and expose this to other kernel drivers.

Note that upon a successful MEM_LEND request the caller must ensure that
the memory region specified is not accessed until a successful
MEM_RECALIM call has been made. On systems with a hypervisor present
this will been enforced, however on systems without a hypervisor the
responsibility falls to the calling kernel driver to prevent access.

Link: https://lore.kernel.org/r/20211015165742.2513065-1-marc.bonnici@arm.com
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_ffa/driver.c

@@ -613,13 +613,30 @@ ffa_memory_share(struct ffa_device *dev, struct ffa_mem_ops_args *args)
 	return ffa_memory_ops(FFA_FN_NATIVE(MEM_SHARE), args);
 }
 
+static int
+ffa_memory_lend(struct ffa_device *dev, struct ffa_mem_ops_args *args)
+{
+	/* Note that upon a successful MEM_LEND request the caller
+	 * must ensure that the memory region specified is not accessed
+	 * until a successful MEM_RECALIM call has been made.
+	 * On systems with a hypervisor present this will been enforced,
+	 * however on systems without a hypervisor the responsibility
+	 * falls to the calling kernel driver to prevent access.
+	 */
+	if (dev->mode_32bit)
+		return ffa_memory_ops(FFA_MEM_LEND, args);
+
+	return ffa_memory_ops(FFA_FN_NATIVE(MEM_LEND), args);
+}
+
 static const struct ffa_dev_ops ffa_ops = {
 	.api_version_get = ffa_api_version_get,
 	.partition_info_get = ffa_partition_info_get,
 	.mode_32bit_set = ffa_mode_32bit_set,
 	.sync_send_receive = ffa_sync_send_receive,
 	.memory_reclaim = ffa_memory_reclaim,
 	.memory_share = ffa_memory_share,
+	.memory_lend = ffa_memory_lend,
 };
 
 const struct ffa_dev_ops *ffa_dev_ops_get(struct ffa_device *dev)

include/linux/arm_ffa.h

@@ -262,6 +262,8 @@ struct ffa_dev_ops {
 	int (*memory_reclaim)(u64 g_handle, u32 flags);
 	int (*memory_share)(struct ffa_device *dev,
 			    struct ffa_mem_ops_args *args);
+	int (*memory_lend)(struct ffa_device *dev,
+			   struct ffa_mem_ops_args *args);
 };
 
 #endif /* _LINUX_ARM_FFA_H */