Subject: Re: [PATCH v4 18/24] iommu/arm-smmu-v3: Introduce master->ats_broken flag

From: Jason Gunthorpe <[email-masked]>
Date: Mon, 1 Jun 2026 09:32:31 -0300

On Fri, May 29, 2026 at 06:27:40PM -0700, Nicolin Chen wrote:
> On Tue, May 19, 2026 at 09:06:58AM -0300, Jason Gunthorpe wrote:
> > On Mon, May 18, 2026 at 08:39:01PM -0700, Nicolin Chen wrote:
> > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > index cde2ff2dcc49b..638956e2535b4 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > @@ -2429,6 +2429,10 @@ static int arm_smmu_atc_inv_master(struct arm_smmu_master *master,
> > >  	struct arm_smmu_cmd cmd;
> > >  	struct arm_smmu_cmdq_batch cmds;
> > >  
> > > +	/* Do not issue ATC_INV that will definitely time out */
> > > +	if (READ_ONCE(master->ats_broken))
> > > +		return 0;
> > > +
> > >  	cmd = arm_smmu_make_cmd_atc_inv_all(0, IOMMU_NO_PASID);
> > >  	arm_smmu_cmdq_batch_init_cmd(master->smmu, &cmds, &cmd);
> > >  	for (i = 0; i < master->num_streams; i++)
> > > @@ -2651,12 +2655,18 @@ static void __arm_smmu_domain_inv_range(struct arm_smmu_invs *invs,
> > >  						       cur->id));
> > >  			break;
> > >  		case INV_TYPE_ATS:
> > > +			/* Do not issue ATC_INV that will definitely time out */
> > > +			if (READ_ONCE(cur->master->ats_broken))
> > > +				break;
> > 
> > Yuk, this should be a bool in the invs list, not the master.
> > 
> > If the flow is to have the core code always attach a blocked domain before
> > reset_done then the invs list will naturally fix itself.
> 
> So I've tried INV_TYPE_ATS_BROKEN: during per-domain invalidation,
> each batch is built from domain->invs so it can carry the "invs";
> if the batch times out, we can immediately mutate its ATS entries.
> 
> But I realized a limitation. E.g., if a device attaches to two SVA
> domains on two SSIDs. An invalidation timing out on one of the SVA
> domains could mark INV_TYPE_ATS_BROKEN in its own invs, but not in
> the other SVA domain's invs?

You'd have to mark all the S1's sharing the STE.

> So, it seems that master->ats_broken is still a cleaner solution?

I don't want the invs code touching master, that is against the entire
design.

Maybe a flag in the invs list itself is sufficient.

Jason