Messages in this thread | | | Date | Tue, 26 Jul 2022 10:57:22 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu interface |
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On Tue, Jul 26, 2022 at 02:23:26PM +0800, Baolu Lu wrote: > On 2022/7/25 22:40, Jason Gunthorpe wrote: > > On Sun, Jul 24, 2022 at 03:03:16PM +0800, Baolu Lu wrote: > > > > > How about rephrasing this part of commit message like below: > > > > > > Some buses, like PCI, route packets without considering the PASID value. > > > Thus a DMA target address with PASID might be treated as P2P if the > > > address falls into the MMIO BAR of other devices in the group. To make > > > things simple, these interfaces only apply to devices belonging to the > > > singleton groups. > > > > > Considering that the PCI bus supports hot-plug, even a device boots with > > > a singleton group, a later hot-added device is still possible to share > > > the group, which breaks the singleton group assumption. In order to > > > avoid this situation, this interface requires that the ACS is enabled on > > > all devices on the path from the device to the host-PCI bridge. > > > > But ACS directly fixes the routing issue above > > > > This entire explanation can be recast as saying we block PASID > > attachment in all cases where the PCI fabric is routing based on > > address. ACS disables that. > > > > Not sure it even has anything to do with hotplug or singleton?? > > Yes, agreed. I polished this patch like below. Does it look good to you? > > iommu: Add attach/detach_dev_pasid iommu interface > > Attaching an IOMMU domain to a PASID of a device is a generic operation > for modern IOMMU drivers which support PASID-granular DMA address > translation. Currently visible usage scenarios include (but not limited): > > - SVA (Shared Virtual Address) > - kernel DMA with PASID > - hardware-assist mediated device > > This adds a pair of domain ops for this purpose and adds the interfaces > for device drivers to attach/detach a domain to/from a {device, > PASID}.
> The PCI bus routes packets without considering the PASID value.
More like:
Some configurations of the PCI fabric will route device originated TLP packets based on memory address, and these configurations are incompatible with PASID as the PASID packets form a distinct address space. For instance any configuration where switches are present without ACS is incompatible with PASID.
> + /* > + * Block PASID attachment in all cases where the PCI fabric is > + * routing based on address. ACS disables it. > + */ > + if (dev_is_pci(dev) && > + !pci_acs_path_enabled(to_pci_dev(dev), NULL, REQ_ACS_FLAGS)) > + return -ENODEV;
I would probably still put this in a function just to be clear, and probably even a PCI layer funcion 'pci_is_pasid_supported' that clearly indicates that the fabric path can route a PASID packet without mis-routing it.
If the fabric routes PASID properly then groups are not an issue - all agree on this?
Jason
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