The initial implementation of PCI/MSI interrupt domains in the hierarchical interrupt domain model used a shortcut by providing a global PCI/MSI domain.
This works because the PCI/MSI[X] hardware is standardized and uniform, but it violates the basic design principle of hierarchical interrupt domains: Each hardware block involved in the interrupt delivery chain should have a separate interrupt domain. For PCI/MSI[X], the interrupt controller is per PCI device and not a global made-up entity. Unsurprisingly, the shortcut turned out to have downsides as it does not allow dynamic allocation of interrupt vectors after initialization and it prevents supporting IMS on PCI. For further details, see: https://lore.kernel.org/lkml/20221111120501.026511...@linutronix.de/ The solution is implementing per device MSI domains, this means the entities which provide global PCI/MSI domain so far have to implement MSI parent domain functionality instead. This series converts the um's driver to implement MSI parent domain. arch/um/drivers/Kconfig | 1 + arch/um/drivers/virt-pci.c | 46 +++++++++++++++++++------------------- 2 files changed, 24 insertions(+), 23 deletions(-) -- 2.39.5
