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

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Message-ID: <32211eb5-eed5-4c71-b62a-362d32e1af47@redhat.com>
Date: Wed, 30 Oct 2024 10:23:39 +1000
From: Gavin Shan <gshan@...hat.com>
To: Jeremy Linton <jeremy.linton@....com>,
 linux-arm-kernel@...ts.infradead.org
Cc: steven.price@....com, suzuki.poulose@....com, catalin.marinas@....com,
 will@...nel.org, sami.mujawar@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: rsi: Add automatic arm-cca-guest module loading

Hi Jeremy,

On 10/30/24 12:11 AM, Jeremy Linton wrote:
> The TSM module provides both guest identification as well as
> attestation when a guest is run in CCA mode. Lets assure by creating a
> dummy platform device that the module is automatically loaded during
> boot. Once it is in place it can be used earlier in the boot process
> to say decrypt a LUKS rootfs.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>   arch/arm64/include/asm/rsi.h                    |  2 ++
>   arch/arm64/kernel/rsi.c                         | 15 +++++++++++++++
>   drivers/virt/coco/arm-cca-guest/arm-cca-guest.c |  7 +++++++
>   3 files changed, 24 insertions(+)
> 

I don't understand how the TSM module is automatically loaded and arm_cca_guest_init()
is triggered because of the newly introduced platform device. Could you please provide
more details? Apart from it, some nick-picks as below.

> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> index 188cbb9b23f5..1b14a4c4257a 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 ARMV9_RSI_PDEV_NAME "arm-cca-dev"
> +

Maybe 'ARMV9' can be avoided since RSI is the specific feature to ARMv9.
Besides, we already had @rsi_present there. So I would suggest to rename
it to RSI_PDEV_NAME

>   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..ad963eb12921 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 = ARMV9_RSI_PDEV_NAME,
> +	.id = -1
> +};
> +

         .id = PLATFORM_DEVID_NONE,

> +static int __init rsi_init(void)
> +{
> +	if (is_realm_world())
> +		if (platform_device_register(&rsi_dev))
> +			pr_err("failed to register rsi platform device");
> +	return 0;
> +}
> +

Those two checks can be connected with '&&' and '\n' seems missed in the
error message.

         if (is_realm_world() && platform_device_register(&rsi_dev))
             pr_err("Failed to register RSI platform device\n");

> +arch_initcall(rsi_init)
> 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..e7ef3b83d5d9 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 +220,12 @@ static void __exit arm_cca_guest_exit(void)
>   }
>   module_exit(arm_cca_guest_exit);
>   
> +static const struct platform_device_id arm_cca_match[] = {
> +	{ ARMV9_RSI_PDEV_NAME, 0},
> +	{ }
> +};
> +
> +MODULE_DEVICE_TABLE(platform, arm_cca_match);


/* Comments here to explain why @arm_cca_dev_ids[] is needed */
static const struct platform_device_id arm_cca_dev_ids[] = {
        ...
};

MODULE_DEVICE_TABLE(platform, arm_cca_dev_ids);

>   MODULE_AUTHOR("Sami Mujawar <sami.mujawar@....com>");
>   MODULE_DESCRIPTION("Arm CCA Guest TSM Driver");
>   MODULE_LICENSE("GPL");

Thanks,
Gavin