Re: [PATCH v12 10/10] iommu/arm-smmu-v3: Add stall support for platform devices

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Sun, Jan 31, 2021 at 07:29:09PM +0100, Auger Eric wrote:
> Hi Jean,
> 
> Some rather minor comments§questions below that may not justify a respin.
> 
> On 1/27/21 4:43 PM, Jean-Philippe Brucker wrote:
> > -static bool arm_smmu_iopf_supported(struct arm_smmu_master *master)
> > +bool arm_smmu_master_iopf_supported(struct arm_smmu_master *master)
> >  {
> > -	return false;
> > +	/* We're not keeping track of SIDs in fault events */
> shall we? [*] below

That would require storing the incoming SID into the iommu_fault_event
struct, and retrieve it in arm_smmu_page_response(). Easy enough, but I
don't think it's needed for existing devices.

> > +	if (master->num_streams != 1)
> > +		return false;
[...]
> > +static int arm_smmu_page_response(struct device *dev,
> > +				  struct iommu_fault_event *unused,
> > +				  struct iommu_page_response *resp)
> > +{
> > +	struct arm_smmu_cmdq_ent cmd = {0};
> > +	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> > +	int sid = master->streams[0].id;
> [*]
> > +
> > +	if (master->stall_enabled) {
> > +		cmd.opcode		= CMDQ_OP_RESUME;
> > +		cmd.resume.sid		= sid;
> > +		cmd.resume.stag		= resp->grpid;
> > +		switch (resp->code) {
> > +		case IOMMU_PAGE_RESP_INVALID:
> add fallthrough?

I think fallthrough is mainly useful to tell reader and compiler that a
break was omitted on purpose. When two cases are stuck together the intent
to merge the flow is clear enough in my opinion. GCC's
-Wimplicit-fallthrough doesn't warn in this case.

> > +		case IOMMU_PAGE_RESP_FAILURE:
> > +			cmd.resume.resp = CMDQ_RESUME_0_RESP_ABORT;
> > +			break;
[...]
> > +static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
> > +{
> > +	int ret;
> > +	u32 reason;
> > +	u32 perm = 0;
> > +	struct arm_smmu_master *master;
> > +	bool ssid_valid = evt[0] & EVTQ_0_SSV;
> > +	u32 sid = FIELD_GET(EVTQ_0_SID, evt[0]);
> > +	struct iommu_fault_event fault_evt = { };
> > +	struct iommu_fault *flt = &fault_evt.fault;
> > +
> > +	/* Stage-2 is always pinned at the moment */
> > +	if (evt[1] & EVTQ_1_S2)
> > +		return -EFAULT;
> > +
> > +	master = arm_smmu_find_master(smmu, sid);
> > +	if (!master)
> > +		return -EINVAL;
> > +
> > +	if (evt[1] & EVTQ_1_RnW)
> > +		perm |= IOMMU_FAULT_PERM_READ;
> > +	else
> > +		perm |= IOMMU_FAULT_PERM_WRITE;
> > +
> > +	if (evt[1] & EVTQ_1_InD)
> > +		perm |= IOMMU_FAULT_PERM_EXEC;
> > +
> > +	if (evt[1] & EVTQ_1_PnU)
> > +		perm |= IOMMU_FAULT_PERM_PRIV;
> > +
> > +	switch (FIELD_GET(EVTQ_0_ID, evt[0])) {
> > +	case EVT_ID_TRANSLATION_FAULT:
> > +	case EVT_ID_ADDR_SIZE_FAULT:
> > +	case EVT_ID_ACCESS_FAULT:
> > +		reason = IOMMU_FAULT_REASON_PTE_FETCH;
> Doesn't it rather map to IOMMU_FAULT_REASON_ACCESS?
> /* access flag check failed */"

Good point, I guess it didn't exist when I wrote this. And ADDR_SIZE_FAULT
corresponds to IOMMU_FAULT_REASON_OOR_ADDRESS now, right?

By the way the wording on those two fault reasons, "access flag" and
"stage", seems arch-specific - x86 names are "accessed flag" and "level".

> > +		break;
> > +	case EVT_ID_PERMISSION_FAULT:
> > +		reason = IOMMU_FAULT_REASON_PERMISSION;
> > +		break;
> > +	default:
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	if (evt[1] & EVTQ_1_STALL) {
> > +		flt->type = IOMMU_FAULT_PAGE_REQ;
> > +		flt->prm = (struct iommu_fault_page_request) {
> > +			.flags = IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE,
> > +			.grpid = FIELD_GET(EVTQ_1_STAG, evt[1]),
> > +			.perm = perm,
> > +			.addr = FIELD_GET(EVTQ_2_ADDR, evt[2]),
> > +		};
> > +
> > +		if (ssid_valid) {
> > +			flt->prm.flags |= IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
> > +			flt->prm.pasid = FIELD_GET(EVTQ_0_SSID, evt[0]);
> > +		}
> > +	} else {
> > +		flt->type = IOMMU_FAULT_DMA_UNRECOV;
> > +		flt->event = (struct iommu_fault_unrecoverable) {
> > +			.reason = reason,
> > +			.flags = IOMMU_FAULT_UNRECOV_ADDR_VALID |
> > +				 IOMMU_FAULT_UNRECOV_FETCH_ADDR_VALID,
> nit: shall IOMMU_FAULT_UNRECOV_FETCH_ADDR_VALID be set here? Supported
> unrecoverable faults feature the IPA field which is UNKNOWN for S1
> translations. fetch_addr rather was
> corresponding to WALK_EABT.Fetch_addr to me.

Right I should drop the IPA part entirely, since we don't report S2 faults
in this patch.

Thanks,
Jean

> > +			.perm = perm,
> > +			.addr = FIELD_GET(EVTQ_2_ADDR, evt[2]),
> > +			.fetch_addr = FIELD_GET(EVTQ_3_IPA, evt[3]),
> > +		};