linux-kernel - Re: [PATCH] KVM: arm64: Fix error checking for FFA

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Message-ID: <aV_RnY1v2We1ajFM@willie-the-truck>
Date: Thu, 8 Jan 2026 15:47:41 +0000
From: Will Deacon <will@...nel.org>
To: Kornel Dulęba <korneld@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oupton@...nel.org>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Bartlomiej Grzesik <bgrzesik@...gle.com>,
	Tomasz Nowicki <tnowicki@...gle.com>,
	Sebastian Ene <sebastianene@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix error checking for FFA_VERSION

On Fri, Nov 14, 2025 at 11:11:53AM +0000, Kornel Dulęba wrote:
> According to section 13.2 of the DEN0077 FF-A specification, when
> firmware does not support the requested version, it should reply with
> FFA_RET_NOT_SUPPORTED(-1). Table 13.6 specifies the type of the error
> code as int32.
> Currently, the error checking logic compares the unsigned long return
> value it got from the SMC layer, against a "-1" literal. This fails due
> to a type mismatch: the literal is extended to 64 bits, whereas the
> register contains only 32 bits of ones(0x00000000ffffffff).
> Consequently, hyp_ffa_init misinterprets the "-1" return value as an
> invalid FF-A version. This prevents pKVM initialization on devices where
> FF-A is not supported in firmware.
> Fix this by explicitly casting res.a0 to s32.
> 
> Signed-off-by: Kornel Dulęba <korneld@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 58b7d0c477d7fce235fc70d089d175c7879861b5..ab1e53bd4ceeea431fc30a875482ed1523b01ab5 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -792,7 +792,7 @@ static void do_ffa_version(struct arm_smccc_1_2_regs *res,
>  			.a0 = FFA_VERSION,
>  			.a1 = ffa_req_version,
>  		}, res);
> -		if (res->a0 == FFA_RET_NOT_SUPPORTED)
> +		if ((s32)res->a0 == FFA_RET_NOT_SUPPORTED)
>  			goto unlock;
>  
>  		hyp_ffa_version = ffa_req_version;
> @@ -943,7 +943,7 @@ int hyp_ffa_init(void *pages)
>  		.a0 = FFA_VERSION,
>  		.a1 = FFA_VERSION_1_2,
>  	}, &res);
> -	if (res.a0 == FFA_RET_NOT_SUPPORTED)
> +	if ((s32)res.a0 == FFA_RET_NOT_SUPPORTED)
>  		return 0;
>  
>  	/*

Acked-by: Will Deacon <will@...nel.org>

Will