Re: [PATCH 2/2] KVM: arm64: support optional calls of FF-A v1.2

[Per Larsen]

Hi Yeoreum,

On 10/29/25 2:36 PM, Yeoreum Yun wrote:
> Hi Ben,
>
> > On 10/28/25 21:06, Yeoreum Yun wrote:
> > > Hi Ben,
> > >
> > > > > To use TPM drvier which uses CRB over FF-A with FFA_DIRECT_REQ2,
> > > > > support the FF-A v1.2's optinal calls by querying whether
> > > > > SPMC supports those.
> > > > >
> > > > > Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> > > > > ---
> > > > >   arch/arm64/kvm/hyp/nvhe/ffa.c | 19 ++++++++++++++++++-
> > > > >   1 file changed, 18 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > > > index 0ae87ff61758..9ded1c6369b9 100644
> > > > > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > > > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > > > > @@ -646,6 +646,22 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
> > > > >   		ffa_to_smccc_res(res, ret);
> > > > >   }
> > > > >
> > > > > +static bool ffa_1_2_optional_calls_supported(u64 func_id)
> > > > > +{
> > > > > +	struct arm_smccc_1_2_regs res;
> > > > > +
> > > > > +	if (!smp_load_acquire(&has_version_negotiated) ||
> > > > > +		(FFA_MINOR_VERSION(FFA_VERSION_1_2) < 2))
> > > > > +		return false;
> > > > > +
> > > > > +	arm_smccc_1_2_smc(&(struct arm_smccc_1_2_regs) {
> > > > > +		.a0 = FFA_FEATURES,
> > > > > +		.a1 = func_id,
> > > > > +	}, &res);
> > > > > +
> > > > > +	return res.a0 == FFA_SUCCESS;
> > > > > +}
> > > > > +
> > > > >   /*
> > > > >    * Is a given FFA function supported, either by forwarding on directly
> > > > >    * or by handling at EL2?
> > > > > @@ -678,12 +694,13 @@ static bool ffa_call_supported(u64 func_id)
> > > > >   	case FFA_NOTIFICATION_SET:
> > > > >   	case FFA_NOTIFICATION_GET:
> > > > >   	case FFA_NOTIFICATION_INFO_GET:
> > > > > +		return false;
> > > > >   	/* Optional interfaces added in FF-A 1.2 */
> > > > >   	case FFA_MSG_SEND_DIRECT_REQ2:		/* Optional per 7.5.1 */
> > > > >   	case FFA_MSG_SEND_DIRECT_RESP2:		/* Optional per 7.5.1 */
> > > > >   	case FFA_CONSOLE_LOG:			/* Optional per 13.1: not in Table 13.1 */
> > > >
> > > > Looking at table 13.54 in the FF-A 1.2 spec FFA_CONSOLE_LOG is only supported in secure FF-A
> > > > instances and not from the normal world.
> > >
> > > Thanks. in that case, we can return false for FFA_CONSOLE_LOG
> > > unconditionally.
> > >
> > > > >   	case FFA_PARTITION_INFO_GET_REGS:	/* Optional for virtual instances per 13.1 */
> > > > > -		return false;
> > > > > +		return ffa_1_2_optional_calls_supported(func_id);
> > > > >   	}
> > > >
> > > > I don't think that an smc call here is the right thing to do. This changes this from a light
> > > > weight deny list to an extra smc call for each ffa_msg_send_direct_req2 from the driver.
> > > >
> > > > Instead, I would expect this patch just to remove FFA_MSG_SEND_DIRECT_REQ2 from the deny list
> > > > and rely on the TPM driver to use FFA_FEATURES to check whether it's supported.
> > > >
> > > > So, just this change:
> > > >
> > > > @@ -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 */
> > > >          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 */
> > > >
> > > > Am I missing something?
> > >
> > > Nope. I think you don't think you miss anything and
> > > I also think about it.
> > >
> > > But, I'm not sure about "support" means in the pkvm about FF-A.
> > > Anyway unless the SPMC doesn't support the specific FF-A ABI,
> > > I don't know that's meaningful to return "TRUE" in here.
> > > IOW, suppose pkvm returns supports of  FFA_MSG_SEND_DIRECT_REQ2
> > > but user receive when it calls FFA_MSG_SEND_DIRECT_REQ2 with NOT SUPPORTED.
> >
> > As I understand it, the ffa_call_supported() is used in two places:
> > 1. To return NOT SUPPORTED to an FFA_FEATURE call for ffa calls that are
> > on the deny list.
> > 2. To block ffa calls if they are on the deny list.
> >
> > For both your patch and just removing FFA_MSG_SEND_DIRECT_REQ2 from the
> > denylist I think the behaviour is the same.
> >
> > If FFA_MSG_SEND_DIRECT_REQ2 is not supported at the spmc then:
> > a) an FFA_FEATURE call will return not supported
> > b) an FFA_MSG_SEND_DIRECT_REQ2 will return not supported
>
> Right! I've missed the FFA_FEATURE handles via default_host_smc_handler().
> As you said, it just a deny list.
>
> Thanks. I'll change it.
Sorry to jump into the discussion very late. I uploaded a patch set 
which adds support for the FFA_MSG_SEND_DIRECT_REQ2 interface which was 
originally developed for the Android common kernels:

https://lore.kernel.org/all/20251030-host-direct-messages-v1-0-463e57871c8f@xxxxxxxxxx/T/#t 


Since there appears to be an upstream use case for this functionality, 
it might be a good building block for the present patch set.

Thanks,
Per