On 18/09/2026 19:30, Ilias Apalodimas wrote:
> Hi Harsimran
>
>>
>> /**
>> - * setup_mm_hdr() - Allocate a buffer for StandAloneMM and initialize the
>> - * header data.
>> + * get_comm_buf() - Obtain a communication buffer for MM/FF-A exchange
>> + * @payload_size: size of the payload that will be appended to the
>> + * MM communication header
>> + *
>> + * This helper returns a buffer suitable for constructing an
>> + * EFI_MM_COMMUNICATE message. During the boot phase a new buffer is
>> + * dynamically allocated. After ExitBootServices(), dynamic
>> + * allocation is no longer permitted, and all runtime communication must
>> + * use the statically reserved FF-A shared buffer.
>> + *
>> + * The caller owns the returned buffer only during the boot phase and
>> + * must release it with free(). During the runtime phase, the returned
>> + * pointer aliases the static FF-A shared buffer and must not be freed.
>> + *
>> + * Return:
>> + * Pointer to a valid communication buffer on success.
>> + * NULL if no suitable communication buffer is available.
>> + */
>> +static __efi_runtime u8 *get_comm_buf(efi_uintn_t payload_size)
>> +{
>> + efi_uintn_t comm_buf_size;
>> + u8 *comm_buf;
>> +
>> + comm_buf_size = MM_COMMUNICATE_HEADER_SIZE +
>> + MM_VARIABLE_COMMUNICATE_SIZE +
>> + payload_size;
>> +
>> + /*
>> + * After ExitBootServices(), dynamic allocation is no longer permitted.
>> + * Use the predefined FF-A shared buffer at runtime; otherwise allocate
>> + * a fresh buffer during the boot phase.
>> + */
>> + if (efi_at_runtime()) {
>> +#if CONFIG_IS_ENABLED(ARM_FFA_TRANSPORT)
>> + if (IS_ENABLED(CONFIG_ARM_FFA_RT_MODE)) {
>> + if (comm_buf_size > CONFIG_FFA_SHARED_MM_BUF_SIZE)
>> + return NULL;
>> + comm_buf = ffa_shared_buf;
>> + if (!comm_buf)
>> + return NULL;
>> + efi_memset_runtime(comm_buf, 0, comm_buf_size);
>> + } else {
>> + return NULL;
>
> This is problematic for the existing use case. With the changes in the later
> patches
> that swap all runtime call unconditionally every call to setup_mm_hdr() will
> return
> EFI_OUT_OF_RESOURCES and none of the runtime services will work without FF-A.
> There's nothing elegant we can do about this .We either Let the fucntions
> from efi_var_common.c
> deal with the runtime part (which I think I prefer), or we define a similar
> runtime
> available buffer for comm_buf.
>
Thanks Ilias.
Yes, I agree this would break the existing non-FF-A runtime path once
the later patches install the TEE runtime handlers unconditionally.
I am planning to keep the existing efi_var_common.c runtime handlers for
the non-FF-A case, and only replace the runtime service table with the
TEE/FF-A runtime handlers when CONFIG_ARM_FFA_RT_MODE is enabled. That
keeps the existing OP-TEE behaviour unchanged, while the FF-A runtime
transport continues to use the static shared buffer after
ExitBootServices().
Does that approach make sense to you?
Regards
Harsimran Singh Tungal>> + }
>> +#else
>> + return NULL;
>> +#endif
>> + } else {
>> + comm_buf = calloc(1, comm_buf_size);
>> + if (!comm_buf)
>> + return NULL;
>> + }
>> + return comm_buf;
>> +}
>> +
>> +/**
>> +static __efi_runtime u8 *setup_mm_hdr(void **dptr, efi_uintn_t payload_size,
>> + efi_uintn_t func, efi_status_t *ret)
>> {
>> - const efi_guid_t mm_var_guid = EFI_MM_VARIABLE_GUID;
>> + static const __efi_runtime_rodata efi_guid_t mm_var_guid =
>> + EFI_MM_VARIABLE_GUID;
>> struct efi_mm_communicate_header *mm_hdr;
>> struct smm_variable_communicate_header *var_hdr;
>> u8 *comm_buf;
>> @@ -555,16 +615,15 @@ static u8 *setup_mm_hdr(void **dptr, efi_uintn_t
>> payload_size,
>> return NULL;
>> }
>>
>> - comm_buf = calloc(1, MM_COMMUNICATE_HEADER_SIZE +
>> - MM_VARIABLE_COMMUNICATE_SIZE +
>> - payload_size);
>> + comm_buf = get_comm_buf(payload_size);
>> if (!comm_buf) {
>> *ret = EFI_OUT_OF_RESOURCES;
>> return NULL;
>> }
>>
>> mm_hdr = (struct efi_mm_communicate_header *)comm_buf;
>> - guidcpy(&mm_hdr->header_guid, &mm_var_guid);
>> + efi_memcpy_runtime(&mm_hdr->header_guid, &mm_var_guid,
>> + sizeof(mm_hdr->header_guid));
>> mm_hdr->message_len = MM_VARIABLE_COMMUNICATE_SIZE + payload_size;
>>
>> var_hdr = (struct smm_variable_communicate_header *)mm_hdr->data;
>> @@ -1077,6 +1136,20 @@ void efi_variables_boot_exit_notify(void)
>> ebs_called = true;
>> }
>>
>> +/**
>> + * ffa_shared_buf_notify_virtual_address_map() - SetVirtualAddressMap
>> callback
>> + *
>> + * @event: callback event
>> + * @context: callback context
>> + */
>> +#if CONFIG_IS_ENABLED(ARM_FFA_TRANSPORT) &&
>> IS_ENABLED(CONFIG_ARM_FFA_RT_MODE)
>> +static void EFIAPI __efi_runtime
>> +ffa_shared_buf_notify_virtual_address_map(struct efi_event *event, void
>> *context)
>> +{
>> + efi_convert_pointer(0, (void **)&ffa_shared_buf);
>> +}
>> +#endif
>> +
>> /**
>> * efi_init_variables() - initialize variable services
>> *
>> @@ -1085,6 +1158,9 @@ void efi_variables_boot_exit_notify(void)
>> efi_status_t efi_init_variables(void)
>> {
>> efi_status_t ret;
>> +#if CONFIG_IS_ENABLED(ARM_FFA_TRANSPORT) &&
>> IS_ENABLED(CONFIG_ARM_FFA_RT_MODE)
>> + struct efi_event *event;
>> +#endif
>>
>> /* Create a cached copy of the variables that will be enabled on
>> ExitBootServices() */
>> ret = efi_var_mem_init();
>> @@ -1103,5 +1179,37 @@ efi_status_t efi_init_variables(void)
>> if (ret != EFI_SUCCESS)
>> return ret;
>>
>> +#if CONFIG_IS_ENABLED(ARM_FFA_TRANSPORT) &&
>> IS_ENABLED(CONFIG_ARM_FFA_RT_MODE)
>> + if (IS_ENABLED(CONFIG_ARM_FFA_RT_MODE)) {
>> + /*
>> + * The FF-A shared buffer is accessed by EFI runtime services,
>> so
>> + * keep the resident pointer convertible across
>> + * SetVirtualAddressMap() and mark the region as runtime memory.
>> + *
>> + * CONFIG_FFA_SHARED_MM_BUF_ADDR is expected to be EFI-page
>> aligned.
>> + */
>> + BUILD_BUG_ON(CONFIG_FFA_SHARED_MM_BUF_ADDR & EFI_PAGE_MASK);
>> + ffa_shared_buf = (void *)CONFIG_FFA_SHARED_MM_BUF_ADDR;
>> + ret = efi_create_event(EVT_SIGNAL_VIRTUAL_ADDRESS_CHANGE,
>> + TPL_CALLBACK,
>> +
>> ffa_shared_buf_notify_virtual_address_map,
>> + NULL, NULL, &event);
>> + if (ret != EFI_SUCCESS)
>> + return ret;
>> + ret = efi_add_memory_map(CONFIG_FFA_SHARED_MM_BUF_ADDR,
>> + CONFIG_FFA_SHARED_MM_BUF_SIZE,
>> + EFI_RUNTIME_SERVICES_DATA);
>> + if (ret != EFI_SUCCESS) {
>> + efi_close_event(event);
>> + log_err("EFI: failed to add FF-A shared buffer to
>> runtime map (%lu)\n",
>> + ret);
>> + return ret;
>> + }
>> + log_info("EFI: FF-A shared buffer runtime map: addr=0x%lx
>> size=0x%lx\n",
>> + (ulong)CONFIG_FFA_SHARED_MM_BUF_ADDR,
>> + (ulong)CONFIG_FFA_SHARED_MM_BUF_SIZE);
>> + }
>> +#endif
>> +
>> return EFI_SUCCESS;
>> }
>
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