Re: [PATCH v3 3/3] iommu/s390: implement iommu passthrough via identity domain

Niklas Schnelle
2025-01-29T10:29:59Z

On Fri, 2025-01-24 at 15:17 -0500, Matthew Rosato wrote:
> 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;

The logic here did confuse me resolving the merge conflict with your
other series. Maybe a ternary conves better that this is really about
not applying the flags if the I/O address translation anchor isn't
used. Something like:

fib.iota = iota | ((iota) ? ZPCI_IOTA_RTTO_FLASG : 0);

> 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()
> };

Other than the nit above this all looks good to me and as stated on
other patches I did give this a try in my setup.

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>