Re: [PATCH v2 2/6] firmware: smccc: Detect hypervisor via RSI host call in CCA Realms

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Initialization order bug causes `arm_smccc_hypervisor_has_uuid()` to incorrectly fall back to standard SMC during early boot in a CCA Realm.
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commit 8e27a5d40fac36e0edcb6814624362e892694ac4
Author: Kameron Carr <kameroncarr@linux.microsoft.com>

firmware: smccc: Detect hypervisor via RSI host call in CCA Realms

This commit modifies arm_smccc_hypervisor_has_uuid() to check is_realm_world()
and use an RSI host call to query the hypervisor UUID inside a Realm. It adds
a file-static RSI host call buffer serialized by a spinlock for ARM64.

> diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
> index bdee057db2fd3..a876b7aa2dc99 100644
> --- a/drivers/firmware/smccc/smccc.c
> +++ b/drivers/firmware/smccc/smccc.c
[ ... ]
> @@ -67,12 +73,45 @@ s32 arm_smccc_get_soc_id_revision(void)
>  }
>  EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_revision);
>  
[ ... ]
>  bool arm_smccc_hypervisor_has_uuid(const uuid_t *hyp_uuid)
>  {
>  	struct arm_smccc_res res = {};
>  	uuid_t uuid;
>  
> -	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> +#ifdef CONFIG_ARM64
> +	if (is_realm_world())
> +		arm_smccc_realm_get_hypervisor_uuid(&res);
> +	else
> +#endif

[Severity: Medium]
Will this check evaluate to false during early boot, causing the detection to
incorrectly fall back to the standard SMC conduit?

Looking at setup_arch(), psci_dt_init() executes before arm64_rsi_init() is
called to set up the rsi_present static key used by is_realm_world():

setup_arch() {
    ...
    if (acpi_disabled)
        psci_dt_init();
    else
        psci_acpi_init();

    arm64_rsi_init();
    ...
}

Because psci_dt_init() calls psci_probe(), which calls kvm_init_hyp_services(),
this eventually reaches arm_smccc_hypervisor_has_uuid() before the static key
is initialized. 

Does this sequence cause a silent failure to detect the KVM hypervisor inside
an Arm CCA Realm?

> +		arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID,
> +				     &res);
> +
>  	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
>  		return false;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260625173500.1995481-1-kameroncarr@linux.microsoft.com?part=2