Re: PATCH: Update disable_IO_APIC to use 8-bit destination field (X86_64)

[ebiederm@xmission.com (Eric W. Biederman)]

Benjamin Romer <benjamin.romer@unisys.com> writes:

> On the Unisys ES7000/ONE system, we encountered a problem where
> performing a kexec reboot or dump on any cell other than cell 0 causes
> the system timer to stop working, resulting in a hang during timer
> calibration in the new kernel. 
>
> We traced the problem to one line of code in disable_IO_APIC(), which
> needs to restore the timer's IO-APIC configuration before rebooting. The
> code is currently using the 4-bit physical destination field, rather
> than using the 8-bit logical destination field, and it cuts off the
> upper 4 bits of the timer's APIC ID. If we change this to use the
> logical destination field, the timer works and we can kexec on the upper
> cells. This was tested on two different cells (0 and 2) in an ES7000/ONE
> system.
>
> For reference, the relevant Intel xAPIC spec is kept at
> ftp://download.intel.com/design/chipsets/e8501/datashts/30962001.pdf,
> specifically on page 334.

Looks like good bug hunting.  I will have to look but it might
make more sense to simply fix: struct IO_APIC_route_entry,
or use whatever technique we normally use to generate the io_apic
vectors.

I don't recall enough off of the top of my head to recall what
the discrimination rule between logical and physical is but
I think setting the system in physical mode is a good clue :)

Eric