linux-kernel - Re: [PATCH v4 1/1] arm64: rsi: Add automatic arm-cca-guest module loading

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Message-ID: <ea47035e-c834-4028-b98f-8b88caff929b@arm.com>
Date: Mon, 23 Dec 2024 09:32:28 +0000
From: Steven Price <steven.price@....com>
To: Jeremy Linton <jeremy.linton@....com>,
 linux-arm-kernel@...ts.infradead.org
Cc: suzuki.poulose@....com, gshan@...hat.com, sami.mujawar@....com,
 itaru.kitayama@...ux.dev, catalin.marinas@....com, will@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] arm64: rsi: Add automatic arm-cca-guest module
 loading

On 20/12/2024 18:12, Jeremy Linton wrote:
> The TSM module provides guest identification and attestation when a
> guest runs in CCA realm mode. By creating a dummy platform device,
> let's ensure the module is automatically loaded. The udev daemon loads
> the TSM module after it receives a device addition event. Once that
> happens, it can be used earlier in the boot process to decrypt the
> rootfs.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>

LGTM

Reviewed-by: Steven Price <steven.price@....com>

Thanks,
Steve

> ---
>  arch/arm64/include/asm/rsi.h                    |  2 ++
>  arch/arm64/kernel/rsi.c                         | 15 +++++++++++++++
>  drivers/virt/coco/arm-cca-guest/arm-cca-guest.c |  8 ++++++++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> index 188cbb9b23f5..b42aeac05340 100644
> --- a/arch/arm64/include/asm/rsi.h
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -10,6 +10,8 @@
>  #include <linux/jump_label.h>
>  #include <asm/rsi_cmds.h>
>  
> +#define RSI_PDEV_NAME "arm-cca-dev"
> +
>  DECLARE_STATIC_KEY_FALSE(rsi_present);
>  
>  void __init arm64_rsi_init(void);
> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> index 3031f25c32ef..ce4778141ec7 100644
> --- a/arch/arm64/kernel/rsi.c
> +++ b/arch/arm64/kernel/rsi.c
> @@ -8,6 +8,7 @@
>  #include <linux/psci.h>
>  #include <linux/swiotlb.h>
>  #include <linux/cc_platform.h>
> +#include <linux/platform_device.h>
>  
>  #include <asm/io.h>
>  #include <asm/mem_encrypt.h>
> @@ -140,3 +141,17 @@ 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/arm-cca-guest.c b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
> index 488153879ec9..87f162736b2e 100644
> --- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
> +++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
> @@ -6,6 +6,7 @@
>  #include <linux/arm-smccc.h>
>  #include <linux/cc_platform.h>
>  #include <linux/kernel.h>
> +#include <linux/mod_devicetable.h>
>  #include <linux/module.h>
>  #include <linux/smp.h>
>  #include <linux/tsm.h>
> @@ -219,6 +220,13 @@ static void __exit arm_cca_guest_exit(void)
>  }
>  module_exit(arm_cca_guest_exit);
>  
> +/* 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},
> +	{ }
> +};
> +
> +MODULE_DEVICE_TABLE(platform, arm_cca_match);
>  MODULE_AUTHOR("Sami Mujawar <sami.mujawar@....com>");
>  MODULE_DESCRIPTION("Arm CCA Guest TSM Driver");
>  MODULE_LICENSE("GPL");