On 7/13/23 14:40, Julien Grall wrote: > Hi Stewart, > > On 07/07/2023 02:47, Stewart Hildebrand wrote: >> From: Rahul Singh <rahul.si...@arm.com> >> >> Setting CONFIG_PCI_PASSTHROUGH=y will enable PCI passthrough on ARM, even >> though >> the feature is not yet complete in the current upstream codebase. The >> purpose of >> this is to make it easier to enable the necessary configs (HAS_PCI, >> HAS_VPCI) for >> testing and development of PCI passthrough on ARM. >> >> Since PCI passthrough on ARM is still work in progress at this time, make it >> depend on EXPERT. > > While preparing the patch for committing, I noticed that HAS_PASSTHROUGH > will now allow the user to select one of the IOMMU quarantine options. > > There are three of them right now: > 1. none > 2. basic (i.e. faulting) > 3. scratch page > > The latter is unlikely to work on Arm because we don't setup the scratch > page. AFAIU, for that, we would need to implement the callback > quarantine_init(). > > I would expect 1 and 2 work. That said, I think 1. would behave like 2. > because on Arm the device should not be automatically re-assigned to > dom0. I know this is correct for platform device, but will it be valid > for PCI as well?
In a system with dom0 where the guest is created from the xl toolstack, we rely on "xl pci-assignable-add". Upon domain destruction, the device automatically gets assigned to domIO. However, there's nothing preventing a user from attempting to invoke "xl pci-assignable-remove", which should assign the device back to dom0, but it is not automatic. With dom0less, PCI devices are not deassigned from the domU. > Overall, before enabling HAS_PASSTHROUGH, I think there would be a bit > of tweaking necessary to at least prevent a user to select the option 3 > (either via Kconfig or the command line). And possibly update the > Kconfig for IOMMU_QUARANTINE to reflect the behavior on Arm. OK
