Re: [PATCH v5 1/2] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ in host handler

[Per Larsen <perl@immunant.com>]

On 1/23/26 4:55 AM, Will Deacon wrote:
> Per,
> 
> On Wed, Jan 21, 2026 at 08:27:12AM +0000, Per Larsen via B4 Relay wrote:
>> From: Sebastian Ene <sebastianene@google.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@google.com>
>> Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
>> Signed-off-by: Per Larsen <perlarsen@google.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.

I should have read your feedback more closely and checked against the 
spec. I will add a new mask for bits 31:16 to check sender ID against
HOST_FFA_ID. Sorry to waste a review cycle and your attention on this.

> 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...

Acknowledged; will do! Apologies for the very late reply.