Hi, Jan! On 11/13/20 4:51 PM, Jan Beulich wrote: > On 13.11.2020 15:44, Oleksandr Andrushchenko wrote: >> On 11/13/20 4:38 PM, Jan Beulich wrote: >>> On 13.11.2020 15:32, Oleksandr Andrushchenko wrote: >>>> On 11/13/20 4:23 PM, Jan Beulich wrote: >>>>> Earlier on I didn't say you should get this to work, only >>>>> that I think the general logic around what you add shouldn't make >>>>> things more arch specific than they really should be. That said, >>>>> something similar to the above should still be doable on x86, >>>>> utilizing struct pci_seg's bus2bridge[]. There ought to be >>>>> DEV_TYPE_PCI_HOST_BRIDGE entries there, albeit a number of them >>>>> (provided by the CPUs themselves rather than the chipset) aren't >>>>> really host bridges for the purposes you're after. >>>> You mean I can still use DEV_TYPE_PCI_HOST_BRIDGE as a marker >>>> >>>> while trying to detect what I need? >>> I'm afraid I don't understand what marker you're thinking about >>> here. >> I mean that when I go over bus2bridge entries, should I only work with >> >> those who have DEV_TYPE_PCI_HOST_BRIDGE? > Well, if you're after host bridges - yes. > > Jan
So, I started looking at the bus2bridge and if it can be used for both x86 (and possible ARM) and I have an impression that the original purpose of this was to identify the devices which x86 IOMMU should cover: e.g. I am looking at the find_upstream_bridge users and they are x86 IOMMU and VGA driver. I tried to play with this on ARM, and for the HW platform I have and QEMU I got 0 entries in bus2bridge... This is because of how xen/drivers/passthrough/pci.c:alloc_pdev is implemented (which lives in the common code BTW, but seems to be x86 specific): so, it skips setting up bus2bridge entries for the bridges I have. These are DEV_TYPE_PCIe_BRIDGE and DEV_TYPE_PCI_HOST_BRIDGE. So, the assumption I've made before that I can go over bus2bridge and filter out the "owner" or parent bridge for a given seg:bus doesn't seem to be possible now. Even if I find the parent bridge with xen/drivers/passthrough/pci.c:find_upstream_bridge I am not sure I can get any further in detecting which x86 domain owns this bridge: the whole idea in the x86 code is that Domain-0 is the only possible one here (you mentioned that). So, I doubt if we can still live with is_hardware_domain for now for x86? Thank you in advance, Oleksandr
