Re: [PATCH] PCI: revert "Enable PASID only when ACS RR & UF enabled on upstream path"

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Jan 11, 2023 at 03:17:03PM +0100, Christian König wrote:
> Am 11.01.23 um 15:14 schrieb Jason Gunthorpe:
> > On Wed, Jan 11, 2023 at 09:54:03PM +0800, Baolu Lu wrote:
> > > On 2023/1/11 21:44, Jason Gunthorpe wrote:
> > > > > iommu_enable_pci_caps() in the Intel IOMMU driver. This also does some
> > > > > handling for ATS, so here we could check the info->ats_supported flag if ACS
> > > > > needs to be checked or not.
> > > > *groan*  this is seems wrong 🙁 Lu why are we doing this inside iommu
> > > > drivers instead of in the device drivers to declare they want to use
> > > > PASID?
> > > Currently it's common to enable pasid in the IOMMU drivers, but device
> > > driver has more knowledge of the device, hence it makes more sense to
> > > move pci_enable_pasid() to the device driver.
> > So, lets fix it that way.
> > 
> > Add the flag to the pci_enable_pasid(), set the flag in the AMD
> > IOMMU's special AMD GPU only path assuming the device will always use
> > ATS
> 
> That will fix at least this the AMD use case.
> 
> > Do not set the flag in the other iommu drivers
> 
> Don't we have other hardware which supports ATS as well and might run into
> the same problem?

As I said, I think we have only 1 user of the common PASID API and it
was happy with things as-is, so I think for v6.2 we are fine.

Honestly, not declaring ACS in a 'enterprise' multi-function device is
already kind of sketchy/rare - even if ATS saves things for the PASID
case.

Jason