linux-kernel - Re: [PATCH v7 5/5] KVM: arm64: Support FFA_MSG_SEND_DIRECT

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Message-ID: <25ba5929-79c0-40b8-b529-79a37914605d@immunant.com>
Date: Mon, 21 Jul 2025 15:43:42 -0700
From: Per Larsen <perl@...unant.com>
To: Will Deacon <will@...nel.org>, perlarsen@...gle.com
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
 Zenghui Yu <yuzenghui@...wei.com>, Catalin Marinas
 <catalin.marinas@....com>, Sudeep Holla <sudeep.holla@....com>,
 linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 linux-kernel@...r.kernel.org, ahomescu@...gle.com, armellel@...gle.com,
 arve@...roid.com, ayrton@...gle.com, qperret@...gle.com,
 sebastianene@...gle.com, qwandor@...gle.com
Subject: Re: [PATCH v7 5/5] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ2 in
 host handler



On 7/18/25 6:53 AM, Will Deacon wrote:
> On Tue, Jul 01, 2025 at 10:06:38PM +0000, Per Larsen via B4 Relay wrote:
>> From: Per Larsen <perlarsen@...gle.com>
>>
>> FF-A 1.2 adds the DIRECT_REQ2 messaging interface which is similar to
>> the existing FFA_MSG_SEND_DIRECT_{REQ,RESP} functions except that it
>> uses the SMC calling convention v1.2 which allows calls to use x4-x17 as
>> argument and return registers. Add support for FFA_MSG_SEND_DIRECT_REQ2
>> in the host ffa handler.
>>
>> Signed-off-by: Per Larsen <perlarsen@...gle.com>
>> ---
>>   arch/arm64/kvm/hyp/nvhe/ffa.c | 24 +++++++++++++++++++++++-
>>   include/linux/arm_ffa.h       |  2 ++
>>   2 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
>> index 79d834120a3f3d26e17e9170c60012b60c6f5a5e..21225988a9365219ccfd69e8e599d7403b5cdf05 100644
>> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
>> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
>> @@ -679,7 +679,6 @@ static bool ffa_call_supported(u64 func_id)
>>   	case FFA_NOTIFICATION_GET:
>>   	case FFA_NOTIFICATION_INFO_GET:
>>   	/* Optional interfaces added in FF-A 1.2 */
>> -	case FFA_MSG_SEND_DIRECT_REQ2:		/* Optional per 7.5.1 */
> 
> I think that's the only change needed. In fact, maybe just don't add it
> in the earlier patch?
> 
>>   	case FFA_MSG_SEND_DIRECT_RESP2:		/* Optional per 7.5.1 */
>>   	case FFA_CONSOLE_LOG:			/* Optional per 13.1: not in Table 13.1 */
>>   	case FFA_PARTITION_INFO_GET_REGS:	/* Optional for virtual instances per 13.1 */
>> @@ -862,6 +861,22 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
>>   	hyp_spin_unlock(&host_buffers.lock);
>>   }
>>   
>> +static void do_ffa_direct_msg2(struct arm_smccc_1_2_regs *regs,
>> +			       struct kvm_cpu_context *ctxt,
>> +			       u64 vm_handle)
>> +{
>> +	DECLARE_REG(u32, endp, ctxt, 1);
>> +
>> +	struct arm_smccc_1_2_regs *args = (void *)&ctxt->regs.regs[0];
>> +
>> +	if (FIELD_GET(FFA_SRC_ENDPOINT_MASK, endp) != vm_handle) {
>> +		ffa_to_smccc_error(regs, FFA_RET_INVALID_PARAMETERS);
>> +		return;
>> +	}
> 
> Why do we care about checking the src id? We don't check that for
> FFA_MSG_SEND_DIRECT_REQ and I don't think we need to care about it here
> either.
FFA_MSG_SEND_DIRECT_REQ is handled by do_ffa_direct_msg [0] (in the 
android common kernels, I'm not aware of efforts to upstream this).

I patterned the check in do_ffa_direct_msg2 off the checking done in 
do_ffa_direct_msg. I pressume your reasoning is that this check can
never fail since we pass in HOST_FFA_ID in kvm_host_ffa_handler. My
thinking was that we do need to validate the source ID once we start
using this function for requests that come from a guest VM. I could
of course add the check in an android-specific patch, WDYT is best?

Also note that since do_ffa_direct_msg was switched to use SMCCC 1.2, I 
think it can handle both FFA_MSG_SEND_DIRECT_REQ and 
FFA_MSG_SEND_DIRECT_REQ2. If you agree, should we upstream 
do_ffa_direct_msg and use it to handle both of these direct requests?

[0] 
https://cs.android.com/android/kernel/superproject/+/common-android16-6.12:common/arch/arm64/kvm/hyp/nvhe/ffa.c;l=1446

Thanks,
Per