linux-kernel - Re: [PATCH v5 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT

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Message-ID: <aXNvzxoBXr-oRB8r@willie-the-truck>
Date: Fri, 23 Jan 2026 12:55:43 +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 v5 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in
 host handler

Per,

On Wed, Jan 21, 2026 at 08:27:12AM +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 | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index f731cc4c3f280a32acccca0de92b9ac6c8e05602..9967916278a7ca051500946ef2fcfe7bb40e0e8d 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -862,6 +862,28 @@ 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];
> +
> +	if (vm_handle != HOST_FFA_ID) {
> +		ffa_to_smccc_error(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}

Sorry, but this isn't what I had in mind. 'vm_handle' is just a local
variable and the only caller passes HOST_FFA_ID, so this isn't really
achieving anything.

What you had in v4 dropped the 'vm_handle' argument entirely, which I
think is the right thing to do. However, the FF-A spec encodes the sender
ID in bits 31:16 of register W1 and so _that_ is what I think we should
be checking because _that_ is what the receiver will see.

Honestly, we could avoid quite a lot of these review cycles if you
actually replied to my emails on the list instead of just responding
with a new patch series each time. It's supposed to be a technical
discussion...

Will