[PATCH] tee: optee: ffa: support shared memory offsets on large-page kernels

[Mahantesh Salimath]

OP-TEE FF-A memory objects use 4 KiB pages, while the kernel page
size may be larger. Consequently, tee_shm->offset can be greater than
or equal to FFA_PAGE_SIZE, but OP-TEE rejects such a value in
internal_offs.

Do not encode the excess page offset in offs_low/offs_high. Those
fields describe the logical memref offset and are copied back into
tee_param->shm_offs on return. Folding the page offset into them breaks
parameter round trips when a memref is reused. They are also ignored by
the OPTEE_RPC_CMD_SHM_ALLOC response path, which uses only global_id and
internal_offs to construct the shared-memory mobj.

Instead, start the FF-A descriptor at the 4 KiB page containing the
shared buffer, the same approach as optee_fill_pages_list() in the SMC
ABI. Store the remaining in-page offset in internal_offs and preserve
shm_offs in offs_low/offs_high. This keeps internal_offs within the
FF-A page size, maps RPC allocations at the correct address, and
preserves normal memref offsets across repeated invocations.

Tested on ARMv8-A with 64 KiB PAGE_SIZE. OP-TEE OS ran as a secure
partition under Hafnium (SPMC) over FF-A. Verified registered shared
memory with tee_shm->offset >= 4 KiB, memref reuse on the same
TEEC_Operation, and RPC OPTEE_RPC_CMD_SHM_ALLOC (xtest regression
6007-6009). optee_hello_world, optee_aes, and xtest regression 1005,
1007, 1008, 4001-4003 and 6001-6003 also passed.

Fixes: 4615e5a34b95 ("optee: add FF-A support")
Acked-by: Liming Sun <limings@xxxxxxxxxx>
Acked-by: James Hurley <jahurley@xxxxxxxxxx>
Acked-by: Dave Thompson <davthompson@xxxxxxxxxx>
Signed-off-by: Mahantesh Salimath <mahantesh@xxxxxxxxxx>
---
 drivers/tee/optee/ffa_abi.c   | 66 +++++++++++++++++++++++++++++------
 drivers/tee/optee/optee_msg.h |  4 +--
 2 files changed, 57 insertions(+), 13 deletions(-)

diff --git a/drivers/tee/optee/ffa_abi.c b/drivers/tee/optee/ffa_abi.c
index 633715b98625..2a37e4899dc6 100644
--- a/drivers/tee/optee/ffa_abi.c
+++ b/drivers/tee/optee/ffa_abi.c
@@ -187,6 +187,40 @@ static int optee_ffa_from_msg_param(struct optee *optee,
 	return 0;
 }
 
+/*
+ * OP-TEE FF-A memory objects use 4 KiB pages while the kernel page size may
+ * be larger, for example 64 KiB on arm64. The FF-A descriptor is registered
+ * from the 4 KiB page containing the start of the shared buffer, so
+ * internal_offs is the offset into that page.
+ */
+static void optee_ffa_set_internal_offs(struct optee_msg_param_fmem *fmem,
+					struct tee_shm *shm)
+{
+	size_t page_offs = tee_shm_get_page_offset(shm);
+
+	BUILD_BUG_ON(PAGE_SIZE < FFA_PAGE_SIZE);
+
+	fmem->internal_offs = page_offs & (FFA_PAGE_SIZE - 1);
+}
+
+/*
+ * Keep shm_offs unchanged in offs_low/offs_high: it is returned to callers
+ * and may be reused for a subsequent invocation.
+ */
+static int optee_ffa_set_fmem_offsets(struct optee_msg_param_fmem *fmem,
+				      struct tee_shm *shm, u64 shm_offs)
+{
+	optee_ffa_set_internal_offs(fmem, shm);
+
+	fmem->offs_low = shm_offs;
+	fmem->offs_high = shm_offs >> 32;
+	/* Check that the entire offset could be stored. */
+	if (fmem->offs_high != shm_offs >> 32)
+		return -EINVAL;
+
+	return 0;
+}
+
 static int to_msg_param_ffa_mem(struct optee_msg_param *mp,
 				const struct tee_param *p)
 {
@@ -196,14 +230,8 @@ static int to_msg_param_ffa_mem(struct optee_msg_param *mp,
 		   TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INPUT;
 
 	if (shm) {
-		u64 shm_offs = p->u.memref.shm_offs;
-
-		mp->u.fmem.internal_offs = shm->offset;
-
-		mp->u.fmem.offs_low = shm_offs;
-		mp->u.fmem.offs_high = shm_offs >> 32;
-		/* Check that the entire offset could be stored. */
-		if (mp->u.fmem.offs_high != shm_offs >> 32)
+		if (optee_ffa_set_fmem_offsets(&mp->u.fmem, shm,
+					       p->u.memref.shm_offs))
 			return -EINVAL;
 
 		mp->u.fmem.global_id = shm->sec_world_id;
@@ -284,14 +312,30 @@ static int optee_ffa_shm_register(struct tee_context *ctx, struct tee_shm *shm,
 		.nattrs = 1,
 	};
 	struct sg_table sgt;
+	size_t page_offs;
+	size_t ffa_offs;
+	size_t ffa_size;
 	int rc;
 
+	if (!num_pages)
+		return -EINVAL;
+
 	rc = optee_check_mem_type(start, num_pages);
 	if (rc)
 		return rc;
 
-	rc = sg_alloc_table_from_pages(&sgt, pages, num_pages, 0,
-				       num_pages * PAGE_SIZE, GFP_KERNEL);
+	page_offs = tee_shm_get_page_offset(shm);
+	ffa_offs = round_down(page_offs, FFA_PAGE_SIZE);
+	ffa_size = num_pages * PAGE_SIZE - ffa_offs;
+
+	/*
+	 * Start the FF-A descriptor at the 4 KiB page containing the shared
+	 * buffer, skipping unused leading 4 KiB pages when PAGE_SIZE is
+	 * larger. Same approach as optee_fill_pages_list() in the SMC ABI.
+	 * This leaves only page_offs & (FFA_PAGE_SIZE - 1) for internal_offs.
+	 */
+	rc = sg_alloc_table_from_pages(&sgt, pages, num_pages, ffa_offs,
+				       ffa_size, GFP_KERNEL);
 	if (rc)
 		return rc;
 	args.sg = sgt.sgl;
@@ -458,8 +502,8 @@ static void handle_ffa_rpc_func_cmd_shm_alloc(struct tee_context *ctx,
 		.attr = OPTEE_MSG_ATTR_TYPE_FMEM_OUTPUT,
 		.u.fmem.size = tee_shm_get_size(shm),
 		.u.fmem.global_id = shm->sec_world_id,
-		.u.fmem.internal_offs = shm->offset,
 	};
+	optee_ffa_set_internal_offs(&arg->params[0].u.fmem, shm);
 
 	arg->ret = TEEC_SUCCESS;
 }
diff --git a/drivers/tee/optee/optee_msg.h b/drivers/tee/optee/optee_msg.h
index 7d9b12e71c03..6c3043f8da33 100644
--- a/drivers/tee/optee/optee_msg.h
+++ b/drivers/tee/optee/optee_msg.h
@@ -136,8 +136,8 @@ struct optee_msg_param_rmem {
  * struct optee_msg_param_fmem - FF-A memory reference parameter
  * @offs_low:		lower bits of offset into shared memory reference
  * @offs_high:		higher bits of offset into shared memory reference
- * @internal_offs:	internal offset into the first page of shared memory
- *			reference
+ * @internal_offs:	offset into the first 4 KiB page of the FF-A shared
+ *			memory region
  * @size:		size of the buffer
  * @global_id:		global identifier of the shared memory
  */
-- 
2.43.0