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

[Baolu Lu]

On 2022/9/15 11:22, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, September 13, 2022 5:25 PM
> >
> > 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()
> > ?
>
> Probably intel_iommu_enable_pci_caps()

It's better.

> > > >    		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.
>
> Yes, that is what the first part of this patch fixes.
>
> But my point is about the message that previously PASID was enabled
> only when FEAT_SVA is enabled and now the patch moves it to the
> probe time.
>
> My point is that even in old way iommu_enable_dev_iotlb() was called
> twice: one at probe time and the other at FEAT_SVA. If ATS exists
> then PASID is enabled at probe time already. If ATS doesn't exist then
> PASID is always disabled.
>
> So this patch is really to decouple PASID enabling from ATS and remove
> the unnecessary/duplicated call of iommu_enable_dev_iotlb() in
> intel_iommu_enable_sva().

Yes. Exactly. I will rephrase the commit message and send a v2.

Best regards,
baolu