Re: [PATCH] linux: prevent invalid or unsupportable PIRQsfrom being used

["Jan Beulich" <jbeulich@novell.com>]

>>> "Jan Beulich" <jbeulich@novell.com> 05.11.08 15:13 >>>
>By keeping the respective irq_desc[] entries pointing to no_irq_type,
>setup_irq() (and thus request_irq()) will fail for such IRQs. This
>matches native behavior, which also only installs ioapic_*_type out of
>ioapic_register_intr().
>
>At the same time, make assign_irq_vector() fail not only when Xen
>doesn't support the PIRQ, but also if the IRQ requested doesn't fall
>in the kernel's PIRQ space.

I wrote this in response to a bug report from IBM where on a 4-node box
they would see crashes when trying to request_irq() with an irq greater
or equal to 256 (the box has 387 GSIs). The patch is assumed to fix that
crash, but of course any device at this high an IRQ (and even at ones
slightly below 256, in case MSI took up some of them) will not work, due
to Xen refusing to map a vector for it.

Clearly, growing NR_IRQS will be necessary here, perhaps based on
Linux' x86-64 scheme of assigning IRQs and their vectors on a per-CPU
basis. Are there any plans in that direction?

Jan

P.S. The good news from that report from IBM is that they were able to
bring up 96 processors.