> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Thursday, August 8, 2024 2:19 AM
>
> PCI ATS has a global Smallest Translation Unit field that is located in
> the PF but shared by all of the VFs.
>
> The expectation is that the STU will be set to the root port's global STU
> capability which is driven by the IO page table configuration of the iommu
> HW. Today it becomes set when the iommu driver first enables ATS.
>
> Thus, to enable ATS on the VF, the PF must have already had the correct
> STU programmed, even if ATS is off on the PF.
>
> Unfortunately the PF only programs the STU when the PF enables ATS. The
> iommu drivers tend to leave ATS disabled when IDENTITY translation is
> being used.
Is there more context on this?
Looking at intel-iommu driver ATS is disabled for IDENETITY when
the iommu is in legacy mode:
dmar_domain_attach_device()
{
...
if (sm_supported(info->iommu) || !domain_type_is_si(info->domain))
iommu_enable_pci_caps(info);
...
}
But this follows what VT-d spec says (section 9.3):
TT: Translate Type
10b: Untranslated requests are processed as pass-through. The SSPTPTR
field is ignored by hardware. Translated and Translation Requests are
blocked.
> +/**
> + * pci_prepare_ats - Setup the PS for ATS
> + * @dev: the PCI device
> + * @ps: the IOMMU page shift
> + *
> + * This must be done by the IOMMU driver on the PF before any VFs are
> created to
> + * ensure that the VF can have ATS enabled.
> + *
> + * Returns 0 on success, or negative on failure.
> + */
> +int pci_prepare_ats(struct pci_dev *dev, int ps)
> +{
> + u16 ctrl;
> +
> + if (!pci_ats_supported(dev))
> + return -EINVAL;
> +
> + if (WARN_ON(dev->ats_enabled))
> + return -EBUSY;
> +
> + if (ps < PCI_ATS_MIN_STU)
> + return -EINVAL;
> +
> + if (dev->is_virtfn)
> + return 0;
missed a check that 'ps' matches pf's ats_stu.
> +
> + dev->ats_stu = ps;
> + ctrl = PCI_ATS_CTRL_STU(dev->ats_stu - PCI_ATS_MIN_STU);
> + pci_write_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, ctrl);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_prepare_ats);
> +
Then there is no need to keep the 'ps' parameter in pci_enable_ats().
