linux-kernel - Re: [PATCH v3 1/1] arm64: rsi: Add automatic arm-cca-guest module loading

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Message-ID: <20241211213018.GA17486@willie-the-truck>
Date: Wed, 11 Dec 2024 21:30:19 +0000
From: Will Deacon <will@...nel.org>
To: Jeremy Linton <jeremy.linton@....com>
Cc: linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
	gshan@...hat.com, steven.price@....com, sami.mujawar@....com,
	catalin.marinas@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] arm64: rsi: Add automatic arm-cca-guest module
 loading

On Fri, Dec 06, 2024 at 07:21:28PM -0600, Jeremy Linton wrote:
> The TSM module provides guest identification and attestation when a
> guest runs in CCA 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>
> ---
>  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..5434e5496ac2 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 rsi_init(void)
> +{
> +	if (is_realm_world() &&
> +	    platform_device_register(&rsi_dev))
> +		pr_err("failed to register rsi platform device\n");
> +	return 0;
> +}
> +
> +arch_initcall(rsi_init)

This file already has an arm64_rsi_init()... Ideally, we'd hang this
off the end of that instead of the initcall but I suspect you're going
to tell me that platform_device_register() doesn't like being called
that early?

If so, perhaps arm64_create_dummy_rsi_dev() might be better?

Will