[PATCH 6/6] iommu/s390: implement def_domain_type

Matthew Rosato
2024-12-09T19:24:29Z

On s390, identity domains are only supported under certain virtualization
scenarios. If iommu passthrough is requested but unavailable for a
device, ignore the request and instead fall back to dma-iommu with a
message.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
drivers/iommu/s390-iommu.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index 18979d8109b2..6906e1b5b1b0 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -462,6 +462,28 @@ static void s390_iommu_get_resv_regions(struct device *dev,
}
}

+static int s390_iommu_def_domain_type(struct device *dev)
+{
+ struct zpci_dev *zdev = to_zpci_dev(dev);
+
+ /* If strict DMA is requested this takes priority */
+ if (iommu_dma_is_strict())
+ return IOMMU_DOMAIN_DMA;
+
+ /* DMA_FQ is the default unless passthrough is specified */
+ if (!iommu_default_passthrough())
+ return IOMMU_DOMAIN_DMA_FQ;
+
+ /* If passthrough specified, CLP must indicate it is allowed. */
+ if (zdev->rtr_avail)
+ return IOMMU_DOMAIN_IDENTITY;
+
+ /* If not allowed, fall back to using translation via DMA_FQ */
+ pr_info("Passthrough ignored, translation required for %s.\n",
+ pci_name(to_pci_dev(dev)));
+ return IOMMU_DOMAIN_DMA_FQ;
+}
+
static struct iommu_device *s390_iommu_probe_device(struct device *dev)
{
struct zpci_dev *zdev;
@@ -839,6 +861,7 @@ static const struct iommu_ops s390_iommu_ops = {
.device_group = generic_device_group,
.pgsize_bitmap = SZ_4K,
.get_resv_regions = s390_iommu_get_resv_regions,
+ .def_domain_type = s390_iommu_def_domain_type,
.default_domain_ops = &(const struct iommu_domain_ops) {
.attach_dev = s390_iommu_attach_device,
.map_pages = s390_iommu_map_pages,
--
2.47.0