Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

[Baolu Lu]

On 2022/9/13 16:01, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Monday, September 12, 2022 10:48 AM
> >
> > @@ -1401,7 +1403,6 @@ static void iommu_enable_dev_iotlb(struct
> > device_domain_info *info)
>
> This is not the right name now as dev_iotlb is only related to ATS.

Yes. This name is confusing. Perhaps we can split it into some specific
helpers,

- intel_iommu_enable_pci_ats()
- intel_iommu_enabel_pci_pri()
- intel_iommu_enable_pci_pasid()
?

> >   		info->pfsid = pci_dev_id(pf_pdev);
> >   	}
> >
> > -#ifdef CONFIG_INTEL_IOMMU_SVM
> >   	/* The PCIe spec, in its wisdom, declares that the behaviour of
> >   	   the device if you enable PASID support after ATS support is
> >   	   undefined. So always enable PASID support on devices which
> > @@ -1414,7 +1415,7 @@ static void iommu_enable_dev_iotlb(struct
> > device_domain_info *info)
> >   	    (info->pasid_enabled ? pci_prg_resp_pasid_required(pdev) : 1)
> > &&
> >   	    !pci_reset_pri(pdev) && !pci_enable_pri(pdev, PRQ_DEPTH))
> >   		info->pri_enabled = 1;
> > -#endif
> > +
> >   	if (info->ats_supported && pci_ats_page_aligned(pdev) &&
> >   	    !pci_enable_ats(pdev, VTD_PAGE_SHIFT)) {
> >   		info->ats_enabled = 1;
>
> iommu_enable_dev_iotlb() is currently called both when the device is probed
> and when sva is enabled (which is actually useless). From this angle the commit
> msg is inaccurate.

The logic is a bit tricky. iommu_support_dev_iotlb() only returns a
devinfo pointer when ATS is supported on the device. So, you are right
if device supports both ATS and PASID; otherwise PASID will not be
enabled.

> > diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
> > index 39a06d245f12..b3f40375f214 100644
> > --- a/drivers/iommu/intel/Kconfig
> > +++ b/drivers/iommu/intel/Kconfig
> > @@ -21,6 +21,8 @@ config INTEL_IOMMU
> >   	select IOASID
> >   	select IOMMU_DMA
> >   	select PCI_ATS
> > +	select PCI_PRI
> > +	select PCI_PASID
> >   	help
> >   	  DMA remapping (DMAR) devices support enables independent
> > address
> >   	  translations for Direct Memory Access (DMA) from devices.
> > @@ -48,8 +50,6 @@ config INTEL_IOMMU_DEBUGFS
> >   config INTEL_IOMMU_SVM
> >   	bool "Support for Shared Virtual Memory with Intel IOMMU"
> >   	depends on X86_64
> > -	select PCI_PASID
> > -	select PCI_PRI
> >   	select MMU_NOTIFIER
> >   	select IOASID
>
> this is already selected by CONFIG_INTEL_IOMMU

Yes. Should be removed.

> >   	select IOMMU_SVA
> > --
> > 2.25.1

Best regards,
baolu