linux-kernel - Re: [PATCH v3 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT

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Message-ID: <aV_MnW8cg7IsWPuD@willie-the-truck>
Date: Thu, 8 Jan 2026 15:26:21 +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 v3 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in
 host handler

On Wed, Nov 19, 2025 at 02:07:53AM +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 | 22 ++++++++++++++++++++++
>  include/linux/arm_ffa.h       |  3 +++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 58b7d0c477d7fce235fc70d089d175c7879861b5..a38a3ab497e5eac11777109684a33f02d88d09a1 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -862,6 +862,23 @@ 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,
> +			      u64 vm_handle)
> +{
> +	DECLARE_REG(u32, flags, ctxt, 2);
> +
> +	struct arm_smccc_1_2_regs *args = (void *)&ctxt->regs.regs[0];
> +
> +	/* filter out framework messages */
> +	if (FIELD_GET(FFA_MSG_FLAGS_MSG_TYPE, flags)) {

Wouldn't we be better off just checking that flags is 0? The rest of it
is SBZ or MBZ in the current spec.

> +		ffa_to_smccc_error(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	arm_smccc_1_2_smc(args, res);
> +}
> +
>  bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
>  {
>  	struct arm_smccc_1_2_regs res;
> @@ -920,6 +937,11 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
>  	case FFA_PARTITION_INFO_GET:
>  		do_ffa_part_get(&res, host_ctxt);
>  		goto out_handled;
> +	case FFA_MSG_SEND_DIRECT_REQ:
> +	case FFA_FN64_MSG_SEND_DIRECT_REQ:
> +

Weird whitespace addition ^^

> +		do_ffa_direct_msg(&res, host_ctxt, HOST_FFA_ID);

What's the point of passing HOST_FFA_ID here? Is that supposed to end up
in the Sender ID bits of W1?

Will