Messages in this thread |  | | From | Logan Gunthorpe <> | Date | Thu, 1 Mar 2018 14:26:57 -0700 | Subject | Re: [PATCH v2 04/10] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches |
| |
On 01/03/18 02:21 PM, Alex Williamson wrote: > This is still a pretty terrible solution though, your kernel provider > needs to decide whether they favor device assignment or p2p, because we > can't do both, unless there's a patch I haven't seen yet that allows > boot time rather than compile time configuration. There are absolutely > supported device assignment cases of switches proving isolation between > devices allowing the downstream EPs to be used independently. I think > this is a non-starter for distribution support without boot time or > dynamic configuration. I could imagine dynamic configuration through > sysfs that might trigger a soft remove and rescan of the affected > devices in order to rebuild the IOMMU group. The hard part might be > determining which points to allow that to guarantee correctness. For > instance, upstream switch ports don't actually support ACS, but they'd > otherwise be an obvious concentration point to trigger a > reconfiguration. Thanks,
At this point, I don't expect this to be enabled in any distribution. The use case is for custom hardware intended to do P2P which means they can have a custom kernel with P2P enabled. The default for CONFIG_PCI_P2P is 'no' and I expect it to stay that way for a long time.
Another boot option which has to be set for this to work isn't something we'd like to see.
Logan
|  |