Re: [PATCH] KVM: arm64: Allow pKVM on v1.0 compatible FF-A implementations

[Marc Zyngier <maz@kernel.org>]

On Tue, 18 Jul 2023 19:45:37 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> pKVM initialization fails on systems with v1.1+ FF-A implementations, as
> the hyp does a strict match on the returned version from FFA_VERSION.
> This is a stronger assertion than required by the specification, which
> requires minor revisions be backwards compatible with earlier revisions
> of the same major version.
> 
> Relax the check in hyp_ffa_init() to only test the returned major
> version. Even though v1.1 broke ABI, the expectation is that firmware
> incapable of using the v1.0 ABI return NOT_SUPPORTED instead of a valid
> version.
> 
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 58dcd92bf346..ab4f5d160c58 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -705,7 +705,20 @@ int hyp_ffa_init(void *pages)
>  	if (res.a0 == FFA_RET_NOT_SUPPORTED)
>  		return 0;
>  
> -	if (res.a0 != FFA_VERSION_1_0)
> +	/*
> +	 * Firmware returns the maximum supported version of the FF-A
> +	 * implementation. Check that the returned version is
> +	 * backwards-compatible with the hyp according to the rules in DEN0077A
> +	 * v1.1 REL0 13.2.1.
> +	 *
> +	 * Of course, things are never simple when dealing with firmware. v1.1
> +	 * broke ABI with v1.0 on several structures, which is itself
> +	 * incompatible with the aforementioned versioning scheme. The
> +	 * expectation is that v1.x implementations that do not support the v1.0
> +	 * ABI return NOT_SUPPORTED rather than a version number, according to
> +	 * DEN0077A v1.1 REL0 18.6.4.

To quote someone: "What a great!"

> +	 */
> +	if (FFA_MAJOR_VERSION(res.a0) != 1)
>  		return -EOPNOTSUPP;
>  
>  	arm_smccc_1_1_smc(FFA_ID_GET, 0, 0, 0, 0, 0, 0, 0, &res);
> 
> base-commit: 9d2a55b403eea26cab7c831d8e1c00ef1e6a6850

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.