Re: [PATCH] coco: guest: arm64: Update ARM CCA guest driver

[Jeremy Linton <jeremy.linton@arm.com>]

On 10/8/25 8:27 AM, Aneesh Kumar K.V (Arm) wrote:
> Make preparatory updates to the ARM CCA guest driver:
> 
>   - Switch from using a platform device to a faux device (based on
>     feedback in [1])
>   - Rename the device from `arm-cca-dev` to `arm-rsi-dev`, so that the
>     host driver can register an equivalent `arm-rmi-dev`
> 
> These changes are purely structural and introduce no new functionality.
> Subsequent patches will extend this driver to add guest device
> assignment support.
> 
> [1] https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
> NOTE:
> This patch is sent early outside the patchseries to avoid userspace from
> depending on the presence of the newly introduced platform device.
> The platform device was added in v6.14-rc1.


At this point, changing the platform device name also breaks systemd's 
confidential vm detection, because its using this device name as the 
first step.


> 
>   arch/arm64/include/asm/rsi.h                  |  2 +-
>   arch/arm64/kernel/rsi.c                       | 15 -----
>   drivers/virt/coco/arm-cca-guest/Makefile      |  3 +
>   .../{arm-cca-guest.c => arm-cca.c}            | 65 +++++++++++--------
>   4 files changed, 41 insertions(+), 44 deletions(-)
>   rename drivers/virt/coco/arm-cca-guest/{arm-cca-guest.c => arm-cca.c} (85%)
> 
> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> index b42aeac05340..26ef6143562b 100644
> --- a/arch/arm64/include/asm/rsi.h
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -10,7 +10,7 @@
>   #include <linux/jump_label.h>
>   #include <asm/rsi_cmds.h>
>   
> -#define RSI_PDEV_NAME "arm-cca-dev"
> +#define RSI_DEV_NAME "arm-rsi-dev"
>   
>   DECLARE_STATIC_KEY_FALSE(rsi_present);
>   
> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> index ce4778141ec7..569ef08750e5 100644
> --- a/arch/arm64/kernel/rsi.c
> +++ b/arch/arm64/kernel/rsi.c
> @@ -140,18 +140,3 @@ void __init arm64_rsi_init(void)
>   
>   	static_branch_enable(&rsi_present);
>   }
> -
> -static struct platform_device rsi_dev = {
> -	.name = RSI_PDEV_NAME,
> -	.id = PLATFORM_DEVID_NONE
> -};
> -
> -static int __init arm64_create_dummy_rsi_dev(void)
> -{
> -	if (is_realm_world() &&
> -	    platform_device_register(&rsi_dev))
> -		pr_err("failed to register rsi platform device\n");
> -	return 0;
> -}
> -
> -arch_initcall(arm64_create_dummy_rsi_dev)
> diff --git a/drivers/virt/coco/arm-cca-guest/Makefile b/drivers/virt/coco/arm-cca-guest/Makefile
> index 69eeba08e98a..609462ea9438 100644
> --- a/drivers/virt/coco/arm-cca-guest/Makefile
> +++ b/drivers/virt/coco/arm-cca-guest/Makefile
> @@ -1,2 +1,5 @@
>   # SPDX-License-Identifier: GPL-2.0-only
> +#
>   obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest.o
> +
> +arm-cca-guest-$(CONFIG_TSM) +=  arm-cca.o
> diff --git a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c b/drivers/virt/coco/arm-cca-guest/arm-cca.c
> similarity index 85%
> rename from drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
> rename to drivers/virt/coco/arm-cca-guest/arm-cca.c
> index 0c9ea24a200c..89d9e7f8eb5d 100644
> --- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
> +++ b/drivers/virt/coco/arm-cca-guest/arm-cca.c
> @@ -1,8 +1,9 @@
>   // SPDX-License-Identifier: GPL-2.0-only
>   /*
> - * Copyright (C) 2023 ARM Ltd.
> + * Copyright (C) 2025 ARM Ltd.
>    */
>   
> +#include <linux/device/faux.h>
>   #include <linux/arm-smccc.h>
>   #include <linux/cc_platform.h>
>   #include <linux/kernel.h>
> @@ -181,52 +182,60 @@ static int arm_cca_report_new(struct tsm_report *report, void *data)
>   	return ret;
>   }
>   
> -static const struct tsm_report_ops arm_cca_tsm_ops = {
> +static const struct tsm_report_ops arm_cca_tsm_report_ops = {
>   	.name = KBUILD_MODNAME,
>   	.report_new = arm_cca_report_new,
>   };
>   
> -/**
> - * arm_cca_guest_init - Register with the Trusted Security Module (TSM)
> - * interface.
> - *
> - * Return:
> - * * %0        - Registered successfully with the TSM interface.
> - * * %-ENODEV  - The execution context is not an Arm Realm.
> - * * %-EBUSY   - Already registered.
> - */
> -static int __init arm_cca_guest_init(void)
> +static void unregister_cca_tsm_report(void *data)
> +{
> +	tsm_report_unregister(&arm_cca_tsm_report_ops);
> +}
> +
> +static int cca_tsm_probe(struct faux_device *fdev)
>   {
>   	int ret;
>   
>   	if (!is_realm_world())
>   		return -ENODEV;
>   
> -	ret = tsm_report_register(&arm_cca_tsm_ops, NULL);
> -	if (ret < 0)
> +	ret = tsm_report_register(&arm_cca_tsm_report_ops, NULL);
> +	if (ret < 0) {
>   		pr_err("Error %d registering with TSM\n", ret);
> +		return ret;
> +	}
> +
> +	ret = devm_add_action_or_reset(&fdev->dev, unregister_cca_tsm_report, NULL);
> +	if (ret < 0) {
> +		pr_err("Error %d registering devm action\n", ret);
> +		unregister_cca_tsm_report(NULL);
> +		return ret;
> +	}
>   
>   	return ret;
>   }
> -module_init(arm_cca_guest_init);
>   
> -/**
> - * arm_cca_guest_exit - unregister with the Trusted Security Module (TSM)
> - * interface.
> - */
> -static void __exit arm_cca_guest_exit(void)
> +static struct faux_device *cca_tsm;
> +
> +static const struct faux_device_ops cca_device_ops = {
> +	.probe = cca_tsm_probe,
> +};
> +
> +static int __init cca_tsm_init(void)
>   {
> -	tsm_report_unregister(&arm_cca_tsm_ops);
> +	cca_tsm = faux_device_create(RSI_DEV_NAME, NULL, &cca_device_ops);
> +	if (!cca_tsm)
> +		return -ENOMEM;
> +	return 0;
>   }
> -module_exit(arm_cca_guest_exit);
> +module_init(cca_tsm_init);
>   
> -/* modalias, so userspace can autoload this module when RSI is available */
> -static const struct platform_device_id arm_cca_match[] __maybe_unused = {
> -	{ RSI_PDEV_NAME, 0},
> -	{ }
> -};
> +static void __exit cca_tsm_exit(void)
> +{
> +	faux_device_destroy(cca_tsm);
> +}
> +module_exit(cca_tsm_exit);
>   
> -MODULE_DEVICE_TABLE(platform, arm_cca_match);
>   MODULE_AUTHOR("Sami Mujawar <sami.mujawar@arm.com>");
>   MODULE_DESCRIPTION("Arm CCA Guest TSM Driver");
>   MODULE_LICENSE("GPL");