Re: [PATCH 1/2] KVM: arm64: fix FF-A call failure when ff-a driver is built-in

[Sebastian Ene <sebastianene@google.com>]

On Mon, Oct 27, 2025 at 07:17:28PM +0000, Yeoreum Yun wrote:

Hi Yeoreum,

> Until has_version_negotiated is set to true,
> all FF-A function calls fail except FFA_VERSION.
> The has_version_negotiated flag is set to true when
> the first FFA_VERSION call is made after init_hyp_mode().
> 
> This works fine when the FF-A driver is built as a module,
> since ffa_init() is invoked after kvm_arm_init(), allowing do_ffa_version()
> to set has_version_negotiated to true.
> 
> However, when the FF-A driver is built-in (CONFIG_ARM_FFA_TRANSPORT=y),
> all FF-A calls fail. This happens because ffa_init() runs before
> kvm_arm_init() — the init level of ffa_init() is rootfs_initcall.
> As a result, the hypervisor cannot set has_version_negotiated,
> since the FFA_VERSION call made in ffa_init() does not trap to the hypervisor
> (HCR_EL2.TSC is cleared before kvm_arm_init()).
> 

I understand the reason behind the patch but this is problematic to have
the builtin driver load before pKVM because the hypervisor would be
un-aware of the host mapped buffers. (eg. the call from ffa_rxtx_map is
not trapped because it is too early). Essentially, you will end up
bypassing the hyp FF-A proxy which I think you will want to avoid.

> Consequently, this causes failures when using EFI variable services
> with secure partitions that rely on FFA_SEND_DIRECT_MSG.
> 
> To fix this, call hyp_ffa_post_init() and set has_version_negotiated
> during hyp_ffa_init() when the FF-A driver is built-in (CONFIG_ARM_FFA_TRANSPORT=y).
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 4e16f9b96f63..0ae87ff61758 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -984,5 +984,17 @@ int hyp_ffa_init(void *pages)
>  	};
>  
>  	version_lock = __HYP_SPIN_LOCK_UNLOCKED;
> +
> +	if (IS_BUILTIN(CONFIG_ARM_FFA_TRANSPORT)) {
> +		hyp_spin_lock(&version_lock);
> +		if (hyp_ffa_post_init()) {
> +			hyp_spin_unlock(&version_lock);
> +			return -EOPNOTSUPP;
> +		}
> +
> +		smp_store_release(&has_version_negotiated, true);
> +		hyp_spin_unlock(&version_lock);
> +	}
> +
>  	return 0;
>  }

Thanks,
Sebastian

> -- 
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>