Messages in this thread | | | Date | Fri, 18 Aug 2023 20:10:15 +0100 | Subject | Re: [PATCH v11 4/6] iommu/s390: Force ISM devices to use IOMMU_DOMAIN_DMA | From | Robin Murphy <> |
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On 2023-07-17 12:00, Niklas Schnelle wrote: > ISM devices are virtual PCI devices used for cross-LPAR communication. > Unlike real PCI devices ISM devices do not use the hardware IOMMU but > inspects IOMMU translation tables directly on IOTLB flush (s390 RPCIT > instruction). > > While ISM devices keep their DMA allocations static and only very rarely > DMA unmap at all, For each IOTLB flush that occurs after unmap the ISM > devices will inspect the area of the IOVA space indicated by the flush. > This means that for the global IOTLB flushes used by the flush queue > mechanism the entire IOVA space would be inspected. In principle this > would be fine, albeit potentially unnecessarily slow, it turns out > however that ISM devices are sensitive to seeing IOVA addresses that are > currently in use in the IOVA range being flushed. Seeing such in-use > IOVA addresses will cause the ISM device to enter an error state and > become unusable. > > Fix this by forcing IOMMU_DOMAIN_DMA to be used for ISM devices. This > makes sure IOTLB flushes only cover IOVAs that have been unmapped and > also restricts the range of the IOTLB flush potentially reducing latency > spikes.
Would it not be simpler to return false for IOMMU_CAP_DEFERRED_FLUSH for these devices?
Cheers, Robin.
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> > --- > drivers/iommu/s390-iommu.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c > index f6d6c60e5634..020cc538e4c4 100644 > --- a/drivers/iommu/s390-iommu.c > +++ b/drivers/iommu/s390-iommu.c > @@ -710,6 +710,15 @@ struct zpci_iommu_ctrs *zpci_get_iommu_ctrs(struct zpci_dev *zdev) > return &zdev->s390_domain->ctrs; > } > > +static int s390_iommu_def_domain_type(struct device *dev) > +{ > + struct zpci_dev *zdev = to_zpci_dev(dev); > + > + if (zdev->pft == PCI_FUNC_TYPE_ISM) > + return IOMMU_DOMAIN_DMA; > + return 0; > +} > + > int zpci_init_iommu(struct zpci_dev *zdev) > { > u64 aperture_size; > @@ -789,6 +798,7 @@ static const struct iommu_ops s390_iommu_ops = { > .probe_device = s390_iommu_probe_device, > .probe_finalize = s390_iommu_probe_finalize, > .release_device = s390_iommu_release_device, > + .def_domain_type = s390_iommu_def_domain_type, > .device_group = generic_device_group, > .pgsize_bitmap = SZ_4K, > .get_resv_regions = s390_iommu_get_resv_regions, >
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