Re: [PATCH v4 2/8] firmware: smccc: Add support for Live Firmware Activation (LFA)

[Sudeep Holla <sudeep.holla@kernel.org>]

On Fri, Sep 18, 2026 at 04:11:05PM +0200, Andre Przywara wrote:
> From: Salman Nabi <salman.nabi@arm.com>
> 
> The Arm Live Firmware Activation (LFA) is a specification [1] to describe
> activating firmware components without a reboot. Those components
> (like TF-A's BL31, EDK-II, TF-RMM, secure paylods) would be updated the
> usual way: via fwupd, FF-A or other secure storage methods, or via some
> IMPDEF Out-Of-Bound method. The user can then activate this new firmware,
> at system runtime, without requiring a reboot.
> The specification covers the SMCCC interface to list and query available
> components and eventually trigger the activation.
> 
> Add a new directory under /sys/firmware to present firmware components
> capable of live activation. Each of them is a directory under lfa/,
> and is identified via its GUID. The activation will be triggered by echoing
> "1" into the "activate" file:
> ==========================================
> /sys/firmware/lfa # ls -l . 6c*
> .:
> total 0
> drwxr-xr-x    2 0 0         0 Jan 19 11:33 47d4086d-4cfe-9846-9b95-2950cbbd5a00
> drwxr-xr-x    2 0 0         0 Jan 19 11:33 6c0762a6-12f2-4b56-92cb-ba8f633606d9
> drwxr-xr-x    2 0 0         0 Jan 19 11:33 d6d0eea7-fcea-d54b-9782-9934f234b6e4
> 
> 6c0762a6-12f2-4b56-92cb-ba8f633606d9:
> total 0
> --w-------    1 0        0             4096 Jan 19 11:33 activate
> -r--r--r--    1 0        0             4096 Jan 19 11:33 activation_capable
> -r--r--r--    1 0        0             4096 Jan 19 11:33 activation_pending
> --w-------    1 0        0             4096 Jan 19 11:33 cancel
> -r--r--r--    1 0        0             4096 Jan 19 11:33 cpu_rendezvous
> -r--r--r--    1 0        0             4096 Jan 19 11:33 current_version
> -rw-r--r--    1 0        0             4096 Jan 19 11:33 force_cpu_rendezvous
> -r--r--r--    1 0        0             4096 Jan 19 11:33 may_reset_cpu
> -r--r--r--    1 0        0             4096 Jan 19 11:33 name
> -r--r--r--    1 0        0             4096 Jan 19 11:33 pending_version
> /sys/firmware/lfa/6c0762a6-12f2-4b56-92cb-ba8f633606d9 # grep . *
> grep: activate: Permission denied
> activation_capable:1
> activation_pending:1
> grep: cancel: Permission denied
> cpu_rendezvous:1
> current_version:0.0
> force_cpu_rendezvous:1
> may_reset_cpu:0
> name:TF-RMM
> pending_version:0.0
> /sys/firmware/lfa/6c0762a6-12f2-4b56-92cb-ba8f633606d9 # echo 1 > activate
> [ 2825.797871] Arm LFA: firmware activation succeeded.
> /sys/firmware/lfa/6c0762a6-12f2-4b56-92cb-ba8f633606d9 #
> ==========================================
> 
> [1] https://developer.arm.com/documentation/den0147/latest/
> 
> Signed-off-by: Salman Nabi <salman.nabi@arm.com>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  drivers/firmware/smccc/Kconfig  |  10 +
>  drivers/firmware/smccc/Makefile |   1 +
>  drivers/firmware/smccc/lfa_fw.c | 766 ++++++++++++++++++++++++++++++++
>  drivers/firmware/smccc/smccc.c  |   5 +
>  include/linux/arm-smccc.h       |  15 +
>  5 files changed, 797 insertions(+)
>  create mode 100644 drivers/firmware/smccc/lfa_fw.c
> 

[...]

> diff --git a/drivers/firmware/smccc/lfa_fw.c b/drivers/firmware/smccc/lfa_fw.c
> new file mode 100644
> index 0000000000000..7cf847e102d5a
> --- /dev/null
> +++ b/drivers/firmware/smccc/lfa_fw.c
> @@ -0,0 +1,766 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2025 Arm Limited

2026 ?

[...]

> +
> +/* A list of known GUIDs, to be shown in the "name" sysfs file. */
> +static const struct fw_image_uuid {
> +	const char *name;
> +	const char *uuid;
> +} fw_images_uuids[] = {
> +	{
> +		.name = "TF-A BL31 runtime",
> +		.uuid = "47d4086d-4cfe-9846-9b95-2950cbbd5a00",
> +	},
> +	{
> +		.name = "BL33 non-secure payload",
> +		.uuid = "d6d0eea7-fcea-d54b-9782-9934f234b6e4",
> +	},
> +	{
> +		.name = "TF-RMM",

Names must go as mentioned earlier. And won't the GET_INVENTORY provide
you the list of UUIDs which IMO should eliminate the needs for such static
information in the driver, no ?

> +		.uuid = "6c0762a6-12f2-4b56-92cb-ba8f633606d9",
> +	},
> +};
> +

[...]

> +static unsigned long get_nr_lfa_components(void)
> +{
> +	struct arm_smccc_1_2_regs reg = { 0 };
> +
> +	reg.a0 = ARM_SMCCC_LFA_GET_INFO;
> +	reg.a1 = 0; /* lfa_info_selector = 0 */
> +


DEN0147, Section 2, also says that the caller must use LFA_FEATURES
to ensure that every function other than LFA_VERSION and LFA_FEATURES is
implemented before calling it. This driver defines the LFA_FEATURES
function ID, but never invokes it before using GET_INFO, GET_INVENTORY,
PRIME, ACTIVATE, and CANCEL.

Could probe query all five functions and reject the device if any function
required by the driver is absent?

> +static ssize_t pending_version_show(struct kobject *kobj,
> +				    struct kobj_attribute *attr, char *buf)
> +{
> +	struct fw_image *image = kobj_to_fw_image(kobj);
> +	struct arm_smccc_1_2_regs reg = { 0 };
> +
> +	/*
> +	 * Similar to activation pending, this value can change following an
> +	 * update, we need to retrieve fresh info instead of stale information.
> +	 */
> +	reg.a0 = ARM_SMCCC_LFA_GET_INVENTORY;
> +	reg.a1 = image->fw_seq_id;
> +	arm_smccc_1_2_invoke(&reg, &reg);
> +	if (reg.a0 == LFA_SUCCESS) {
> +		if (reg.a5 != 0 && image->activation_pending) {

Why are you not testing/checking the activation_pending bit in the fresh
reg.a3 value instead of the cached image flag?

Table 2.4.5 makes X5 valid according to the flags returned by the same
LFA_GET_INVENTORY call.

If a component becomes pending after enumeration,reading pending_version
before activation_pending will incorrectly return "N/A" despite the
fresh call reporting a valid X5.

So, I think this needs fixing ?

> +
> +static int lfa_smccc_probe(struct arm_smccc_device *sdev)
> +{
> +	struct arm_smccc_1_2_regs reg = { 0 };
> +	int err;
> +
> +	reg.a0 = ARM_SMCCC_LFA_GET_VERSION;
> +	arm_smccc_1_2_invoke(&reg, &reg);

Check if SMCCC >= v1.2 before using these functions.

> +
> +MODULE_DESCRIPTION("ARM Live Firmware Activation (LFA)");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
> index 5ea3478be9d3c..d7cd01e5c92b8 100644
> --- a/drivers/firmware/smccc/smccc.c
> +++ b/drivers/firmware/smccc/smccc.c
> @@ -94,6 +94,11 @@ static const struct smccc_device_info smccc_devices[] __initconst = {
>  		.requires_smc   = false,
>  		.device_name    = "arm-smccc-trng",
>  	},
> +	{
> +		.func_id        = ARM_SMCCC_LFA_GET_VERSION,
> +		.requires_smc   = false,
> +		.device_name    = "arm-smccc-lfa",
> +	},
>  };
>  

DEN0147, Section 2.1.2, says that the caller must determine that
the SMCCC version is at least 1.2 before calling LFA_VERSION.  The generic
SMCCC probing path only checks that a conduit exists before invoking this
function ID. That could break our SMCCC bus logic. Assuming the firmware
can cope up, it is always good to check the SMCCC version >=v1.2 in the
probe which is not done currently.

-- 
Regards,
Sudeep