linux-kernel - Re: [PATCH v4 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT

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Message-ID: <aW-MugHHrJVQQKxc@willie-the-truck>
Date: Tue, 20 Jan 2026 14:10:02 +0000
From: Will Deacon <will@...nel.org>
To: perlarsen@...gle.com
Cc: Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Yeoreum Yun <yeoreum.yun@....com>, Ben Horgan <ben.horgan@....com>,
	Oliver Upton <oupton@...nel.org>,
	Armelle Laine <armellel@...gle.com>,
	Sebastien Ene <sebastianene@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in
 host handler

On Fri, Jan 09, 2026 at 10:34:25PM +0000, Per Larsen via B4 Relay wrote:
> From: Sebastian Ene <sebastianene@...gle.com>
> 
> Allow direct messages to be forwarded from the host. The host should
> not be sending framework messages so they are filtered out.
> 
> Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> Reviewed-by: Yeoreum Yun <yeoreum.yun@....com>
> Signed-off-by: Per Larsen <perlarsen@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 20 ++++++++++++++++++++
>  include/linux/arm_ffa.h       |  3 +++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index f731cc4c3f280a32acccca0de92b9ac6c8e05602..fc84595007f310004def7d525371fa7c128f244a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -862,6 +862,22 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
>  	hyp_spin_unlock(&host_buffers.lock);
>  }
>  
> +static void do_ffa_direct_msg(struct arm_smccc_1_2_regs *res,
> +			      struct kvm_cpu_context *ctxt)
> +{
> +	DECLARE_REG(u32, flags, ctxt, 2);
> +
> +	struct arm_smccc_1_2_regs *args = (void *)&ctxt->regs.regs[0];
> +
> +	/* filter out framework messages and validate SBZ/MBZ bits */
> +	if (flags) {
> +		ffa_to_smccc_error(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	arm_smccc_1_2_smc(args, res);

I thought we were going to validate that the sender is HOST_FFA_ID?

> diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
> index 81e603839c4a51873090b7e22edbe7b33a7e94df..d209d0cdac1eb804be01e4607acac8f76cc99e40 100644
> --- a/include/linux/arm_ffa.h
> +++ b/include/linux/arm_ffa.h
> @@ -130,6 +130,9 @@
>  #define FFA_FEAT_RXTX_MIN_SZ_16K	2
>  #define FFA_FEAT_RXTX_MIN_SZ_MASK	GENMASK(1, 0)
>  
> +/* FFA message flags */
> +#define FFA_MSG_FLAGS_MSG_TYPE		BIT(31)
> +

This hunk is no longer needed now that we're just checking for the flags
being zero.

Will