On 21.12.2023 14:29, Juergen Gross wrote: > On 21.12.23 13:40, Jan Beulich wrote: >> On 20.12.2023 17:34, Sébastien Chaumat wrote: >>> Here are the patches I made to xen and linux kernel >>> Plus dmesg (bare metal,xen) and "xl dmesg" >> >> So the problem looks to be that pci_xen_initial_domain() results in >> permanent setup of IRQ7, when there only "static" ACPI tables (in >> particular source overrides in MADT) are consulted. The necessary >> settings, however, are known only after _CRS for the device was >> evaluated (and possibly _PRS followed by invocation of _SRS). All of >> this happens before xen_register_gsi() is called. But that function's >> call to xen_register_pirq() is short-circuited by the very first if() >> in xen_register_pirq() when there was an earlier invocation. Hence >> the (wrong) "edge" binding remains in place, as was established by >> the earlier call here. >> >> Jürgen, there's an interesting comment in xen_bind_pirq_gsi_to_irq(), >> right before invoking irq_set_chip_and_handler_name(). Despite what >> the comment says (according to my reading), the fasteoi one is _not_ >> used in all cases. Assuming there's a reason for this, it's not clear >> to me whether updating the handler later on is a valid thing to do. >> __irq_set_handler() being even an exported symbol suggests that might >> be an option to use here. Then again merely updating the handler may >> not be sufficient, seeing there are also e.g. IRQD_TRIGGER_MASK and >> IRQD_LEVEL. > > I understand the last paragraph of that comment to reason, that in case > pirq_needs_eoi() return true even in case of an edge triggered interrupt, > the outcome is still okay. > > I don't think updating the handler later is valid.
In which case fixing this is going to be interesting. >> Jürgen, looking at pci_xen_initial_domain(), what's the purpose of >> the loop in the final if()? Can this ever do anything useful when >> the earlier comment suggests nr_legacy_irqs() is zero anyway? Or is >> the comment simply inaccurate in not covering the "no IO-APICs" case? > > No, I think the final loop would only do something in case probe_8259A() > is detecting a working PIC (which should not be the case IMHO). Could it > be that there have been Xen versions emulating a PIC? Not as far back as I can recall (for PV Dom0). Even in 3.2 Dom0 was already denied access to the respective I/O ports. And iirc upstream Linux wants at least 4.0? Jan
