[PATCH v5 05/27] iommu/arm-smmu-v3: Make CD programming use arm_smmu_write_entry()

[Jason Gunthorpe]

On Tue, Mar 26, 2024 at 07:12:53PM +0000, Mostafa Saleh wrote:
> On Tue, Mar 26, 2024 at 03:30:55PM -0300, Jason Gunthorpe wrote:
> > On Sat, Mar 23, 2024 at 01:02:15PM +0000, Mostafa Saleh wrote:
> > > > +static void arm_smmu_get_cd_used(const __le64 *ent, __le64 *used_bits)
> > > > +{
> > > > +	used_bits[0] = cpu_to_le64(CTXDESC_CD_0_V);
> > > > +	if (!(ent[0] & cpu_to_le64(CTXDESC_CD_0_V)))
> > > > +		return;
> > > > +	memset(used_bits, 0xFF, sizeof(struct arm_smmu_cd));
> > > 
> > > This is a slightly different approach than what the driver does for STEs,
> > > where it explicitly sets the used bits. Is there a reason for that?
> > 
> > It is just more compact this way
> 
> IMHO, it seems too much to have this mechanism for CDs for just one
> SVA case, but I'll need to go through the whole seires first to make
> sure I am not missing anything.

It is pretty ugly if you try to do it that way. You still need to
create some ops because the entry_set should be re-used (I mean I
guess you could copy it as well). Then you have to open code the
logic. And then the EPD0 path is somewhat fragile. Something sort of
like this:

void arm_smmu_write_cd_entry(struct arm_smmu_master *master, int ssid,
			     struct arm_smmu_cd *cdptr,
			     const struct arm_smmu_cd *target)
{
	bool target_valid = target->data[0] & cpu_to_le64(CTXDESC_CD_0_V);
	bool cur_valid = cdptr->data[0] & cpu_to_le64(CTXDESC_CD_0_V);
	struct arm_smmu_cd_writer cd_writer = {
		.writer = {
			.ops = &arm_smmu_cd_writer_ops,
			.master = master,
		},
		.ssid = ssid,
	};

	if (ssid != IOMMU_NO_PASID && cur_valid != target_valid) {
		if (cur_valid)
			master->cd_table.used_ssids--;
		else
			master->cd_table.used_ssids++;
	}

	/* Force a V=0/V=1 update*/
	__le64 update = target[0] & ~cpu_to_le64(CTXDESC_CD_0_V);
	entry_set(&cd_writer.writer, cdptr->data, &update, 0, 1);
	entry_set(&cd_writer.writer, cdptr->data, target->data, 1, NUM_ENTRY_QWORDS - 1);
	entry_set(&cd_writer.writer, cdptr->data, target->data, 0, 1);
}

void arm_smmu_write_cd_entry_epd0(struct arm_smmu_master *master, int ssid,
				  struct arm_smmu_cd *cdptr,
				  const struct arm_smmu_cd *target)
{
	struct arm_smmu_cd_writer cd_writer = {
		.writer = {
			.ops = &arm_smmu_cd_writer_ops,
			.master = master,
		},
		.ssid = ssid,
	};

	/*
	 * Target must the EPD0 = 1 version of the existing CD entry, caller
	 * must enforce it. Assume used_ssids doesn't need updating
	 * for this reason.
	 */
	/* Update EPD0 */
	entry_set(&cd_writer.writer, cdptr->data, target->data, 0, 1);
	/* Update everthing else */
	entry_set(&cd_writer.writer, cdptr->data, target->data, 0, NUM_ENTRY_QWORDS - 1);
}

IMOH, at this point it is saner to have just implemented the used
function and use the mechanism robustly. Less special cases, less
fragility, less duplication.

Jason