linux-kernel - [PATCH] firmware: smccc: support both conduits for getting hyp UUID

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Message-ID: <20250604214522.3523-1-romank@linux.microsoft.com>
Date: Wed,  4 Jun 2025 14:45:21 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: anirudh@...rudhrb.com
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lpieralisi@...nel.org,
	mark.rutland@....com,
	sudeep.holla@....com,
	apais@...rosoft.com,
	benhill@...rosoft.com,
	bperkins@...rosoft.com,
	sunilmut@...rosoft.com
Subject: [PATCH] firmware: smccc: support both conduits for getting hyp UUID

> From: Anirudh Rayabharam (Microsoft) <anirudh@...rudhrb.com>
>
> When Linux is running as the root partition under Microsoft Hypervisor
> (MSHV) a.k.a Hyper-V, smc is used as the conduit for smc calls.
>
> Extend arm_smccc_hypervisor_has_uuid() to support this usecase. Use
> arm_smccc_1_1_invoke to retrieve and use the appropriate conduit instead
> of supporting only hvc.
>
> Boot tested on MSHV guest, MSHV root & KVM guest.
>
> Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@...rudhrb.com>
> ---
>  drivers/firmware/smccc/smccc.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
> index cd65b434dc6e..bdee057db2fd 100644
> --- a/drivers/firmware/smccc/smccc.c
> +++ b/drivers/firmware/smccc/smccc.c
> @@ -72,10 +72,7 @@ bool arm_smccc_hypervisor_has_uuid(const uuid_t *hyp_uuid)
>  	struct arm_smccc_res res = {};
>  	uuid_t uuid;
>
> -	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> -		return false;
> -
> -	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
>  	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
>  		return false;

The patch is a strict superset of the existing functionality.
Validated on baremetal Linux and KVM, Apple M3 nested virt., various client and
server ARM64 systems running Windows ARM64 with VMs managed by Hyper-V and OpenVMM.

Looks good to me.

Tested-by: Roman Kisel <romank@...ux.microsoft.com>
Reviewed-by: Roman Kisel <romank@...ux.microsoft.com>