Re: [PATCH v2 1/7] KVM: arm64: Support FFA_NOTIFICATION_BITMAP_CREATE in host handler

[Vincent Donnefort <vdonnefort@google.com>]

On Wed, Jun 10, 2026 at 09:51:55AM +0100, Vincent Donnefort wrote:
> Hi Seb,
> 
> On Mon, Jun 08, 2026 at 04:55:43PM +0000, Sebastian Ene wrote:
> > Allow FF-A notification bitmap creation messages to be forwarded to
> > Trustzone from the host and introduce a helper to check for SBZ
> > register fields.
> > 
> > Signed-off-by: Sebastian Ene <sebastianene@google.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/ffa.c | 36 ++++++++++++++++++++++++++++++++++-
> >  1 file changed, 35 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > index 1af722771178..c20d45191085 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > @@ -71,6 +71,18 @@ static u32 hyp_ffa_version;
> >  static bool has_version_negotiated;
> >  static hyp_spinlock_t version_lock;
> >  
> > +static bool ffa_check_unused_args_sbz(struct kvm_cpu_context *ctxt, int first_reg)
> > +{
> > +	int reg;
> > +
> > +	for (reg = first_reg; reg < 17; reg++) {
> 
> The upper limit should probably be something like ARRAY_SIZE(ctx->regs.regs) - first_reg?

I wasn't really inspired this morning on the cruiser...

But nonetheless, that 17 should probably be a #define somewhere?
> 
> > +		if (cpu_reg(ctxt, reg))
> > +			return true;
> > +	}
> > +
> > +	return false;
> > +}
> > +
> >  static void ffa_to_smccc_error(struct arm_smccc_1_2_regs *res, u64 ffa_errno)
> >  {
> >  	*res = (struct arm_smccc_1_2_regs) {
> > @@ -676,7 +688,6 @@ static bool ffa_call_supported(u64 func_id)
> >  	case FFA_MEM_DONATE:
> >  	case FFA_MEM_RETRIEVE_REQ:
> >         /* Optional notification interfaces added in FF-A 1.1 */
> > -	case FFA_NOTIFICATION_BITMAP_CREATE:
> >  	case FFA_NOTIFICATION_BITMAP_DESTROY:
> >  	case FFA_NOTIFICATION_BIND:
> >  	case FFA_NOTIFICATION_UNBIND:
> > @@ -862,6 +873,26 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res,
> >  	hyp_spin_unlock(&host_buffers.lock);
> >  }
> >  
> > +static void do_ffa_notif_bitmap_create(struct arm_smccc_1_2_regs *res,
> > +				       struct kvm_cpu_context *ctxt)
> > +{
> > +	DECLARE_REG(u32, vmid, ctxt, 1);
> > +	struct arm_smccc_1_2_regs *args;
> > +
> > +	if (ffa_check_unused_args_sbz(ctxt, 3)) {
> 
> Is that expected we start at 3 but only read 0 and 1?

Ha, we do not read 2 but nonetheless it is useful!

> 
> > +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> > +		return;
> > +	}
> > +
> > +	if (vmid != HOST_FFA_ID) {
> > +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> > +		return;
> > +	}
> > +
> > +	args = (void *)&ctxt->regs.regs[0];
> > +	arm_smccc_1_2_smc(args, res);
> 
> Should be hyp_smccc_1_2_smc()
> 
> > +}
> > +
> >  bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
> >  {
> >  	struct arm_smccc_1_2_regs res;
> > @@ -920,6 +951,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
> >  	case FFA_PARTITION_INFO_GET:
> >  		do_ffa_part_get(&res, host_ctxt);
> >  		goto out_handled;
> > +	case FFA_NOTIFICATION_BITMAP_CREATE:
> > +		do_ffa_notif_bitmap_create(&res, host_ctxt);
> > +		goto out_handled;
> >  	}
> >  
> >  	if (ffa_call_supported(func_id))
> > -- 
> > 2.54.0.1064.gd145956f57-goog
> >