[PATCH v2 3/3] iommu/s390: implement iommu passthrough via identity domain

Matthew Rosato
2024-12-13T22:50:03Z

Enabled via the kernel command-line 'iommu.passthrough=1' option.

Introduce the concept of identity domains to s390-iommu, which relies on
the bus_dma_region to offset identity mappings to the start of the DMA
aperture advertized by CLP.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
arch/s390/pci/pci.c | 6 ++-
drivers/iommu/s390-iommu.c | 95 +++++++++++++++++++++++++++++---------
2 files changed, 76 insertions(+), 25 deletions(-)

diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 88f72745fa59..758b23331754 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -124,14 +124,16 @@ int zpci_register_ioat(struct zpci_dev *zdev, u8 dmaas,
struct zpci_fib fib = {0};
u8 cc;

- WARN_ON_ONCE(iota & 0x3fff);
fib.pba = base;
/* Work around off by one in ISM virt device */
if (zdev->pft == PCI_FUNC_TYPE_ISM && limit > base)
fib.pal = limit + (1 << 12);
else
fib.pal = limit;
- fib.iota = iota | ZPCI_IOTA_RTTO_FLAG;
+ if (iota == 0)
+ fib.iota = iota;
+ else
+ fib.iota = iota | ZPCI_IOTA_RTTO_FLAG;
fib.gd = zdev->gisa;
cc = zpci_mod_fc(req, &fib, status);
if (cc)
diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index fbdeded3d48b..3d93a9644fca 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -16,7 +16,7 @@

#include "dma-iommu.h"

-static const struct iommu_ops s390_iommu_ops;
+static const struct iommu_ops s390_iommu_ops, s390_iommu_rtr_ops;

static struct kmem_cache *dma_region_table_cache;
static struct kmem_cache *dma_page_table_cache;
@@ -392,9 +392,11 @@ static int blocking_domain_attach_device(struct iommu_domain *domain,
return 0;

s390_domain = to_s390_domain(zdev->s390_domain);
- spin_lock_irqsave(&s390_domain->list_lock, flags);
- list_del_rcu(&zdev->iommu_list);
- spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+ if (zdev->dma_table) {
+ spin_lock_irqsave(&s390_domain->list_lock, flags);
+ list_del_rcu(&zdev->iommu_list);
+ spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+ }

zpci_unregister_ioat(zdev, 0);
zdev->dma_table = NULL;
@@ -723,7 +725,13 @@ int zpci_init_iommu(struct zpci_dev *zdev)
if (rc)
goto out_err;

- rc = iommu_device_register(&zdev->iommu_dev, &s390_iommu_ops, NULL);
+ if (zdev->rtr_avail) {
+ rc = iommu_device_register(&zdev->iommu_dev,
+ &s390_iommu_rtr_ops, NULL);
+ } else {
+ rc = iommu_device_register(&zdev->iommu_dev, &s390_iommu_ops,
+ NULL);
+ }
if (rc)
goto out_sysfs;

@@ -787,6 +795,39 @@ static int __init s390_iommu_init(void)
}
subsys_initcall(s390_iommu_init);

+static int s390_attach_dev_identity(struct iommu_domain *domain,
+ struct device *dev)
+{
+ struct zpci_dev *zdev = to_zpci_dev(dev);
+ u8 status;
+ int cc;
+
+ blocking_domain_attach_device(&blocking_domain, dev);
+
+ /* If we fail now DMA remains blocked via blocking domain */
+ cc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
+ 0, &status);
+ /*
+ * If the device is undergoing error recovery the reset code
+ * will re-establish the new domain.
+ */
+ if (cc && status != ZPCI_PCI_ST_FUNC_NOT_AVAIL)
+ return -EIO;
+
+ zdev_s390_domain_update(zdev, domain);
+
+ return 0;
+}
+
+static const struct iommu_domain_ops s390_identity_ops = {
+ .attach_dev = s390_attach_dev_identity,
+};
+
+static struct iommu_domain s390_identity_domain = {
+ .type = IOMMU_DOMAIN_IDENTITY,
+ .ops = &s390_identity_ops,
+};
+
static struct iommu_domain blocking_domain = {
.type = IOMMU_DOMAIN_BLOCKED,
.ops = &(const struct iommu_domain_ops) {
@@ -794,23 +835,31 @@ static struct iommu_domain blocking_domain = {
}
};

-static const struct iommu_ops s390_iommu_ops = {
- .blocked_domain = &blocking_domain,
- .release_domain = &blocking_domain,
- .capable = s390_iommu_capable,
- .domain_alloc_paging = s390_domain_alloc_paging,
- .probe_device = s390_iommu_probe_device,
- .device_group = generic_device_group,
- .pgsize_bitmap = SZ_4K,
- .get_resv_regions = s390_iommu_get_resv_regions,
- .default_domain_ops = &(const struct iommu_domain_ops) {
- .attach_dev = s390_iommu_attach_device,
- .map_pages = s390_iommu_map_pages,
- .unmap_pages = s390_iommu_unmap_pages,
- .flush_iotlb_all = s390_iommu_flush_iotlb_all,
- .iotlb_sync = s390_iommu_iotlb_sync,
- .iotlb_sync_map = s390_iommu_iotlb_sync_map,
- .iova_to_phys = s390_iommu_iova_to_phys,
- .free = s390_domain_free,
+#define S390_IOMMU_COMMON_OPS() \
+ .blocked_domain = &blocking_domain, \
+ .release_domain = &blocking_domain, \
+ .capable = s390_iommu_capable, \
+ .domain_alloc_paging = s390_domain_alloc_paging, \
+ .probe_device = s390_iommu_probe_device, \
+ .device_group = generic_device_group, \
+ .pgsize_bitmap = SZ_4K, \
+ .get_resv_regions = s390_iommu_get_resv_regions, \
+ .default_domain_ops = &(const struct iommu_domain_ops) { \
+ .attach_dev = s390_iommu_attach_device, \
+ .map_pages = s390_iommu_map_pages, \
+ .unmap_pages = s390_iommu_unmap_pages, \
+ .flush_iotlb_all = s390_iommu_flush_iotlb_all, \
+ .iotlb_sync = s390_iommu_iotlb_sync, \
+ .iotlb_sync_map = s390_iommu_iotlb_sync_map, \
+ .iova_to_phys = s390_iommu_iova_to_phys, \
+ .free = s390_domain_free, \
}
+
+static const struct iommu_ops s390_iommu_ops = {
+ S390_IOMMU_COMMON_OPS()
+};
+
+static const struct iommu_ops s390_iommu_rtr_ops = {
+ .identity_domain = &s390_identity_domain,
+ S390_IOMMU_COMMON_OPS()
};
--
2.47.1