Re: [PATCH v7 5/5] KVM: arm64: Support FFA_MSG_SEND_DIRECT_REQ2 in host handler

[Per Larsen]

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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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