Re: [Xen-devel] APIC handling on x86-64

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 17 Mar 2006, at 16:49, Jan Beulich wrote:

> As we had a report of a problem booting Xen on an IBM x460, dying on 
> the BUG_ON() in init_apic_ldr() in
> xen/include/asm-x86/mach-summit/mach_apic.h, I started comparing 32- 
> and 64-bit APIC handling. Quickly I found that the
> same case is handled gracefully in 64-bits, by just tying any extra 
> CPUs to the highest bit. (I suppose, will try to
> verify this with the originator, that the same machine also doesn't 
> boot with native 32-bit Linux, as the exact same
> issue should exist there).
> While doing the same generally shouldn't be a problem, I wonder why 
> this hasn't been discovered so far and how many
> else differences there exist.
Differences between i386 and x86/64 native Linux APIC handling? A fair 
few, although mostly it's because crufty old code has been removed from 
x86/64. I guess there are occasions where Andi Kleen has improved 
correctness at the same time as cleaning up. :-)
This is the first time that the strategy of taking latest i386 APIC 
code has let us down I think.
I guess we just patch it in Xen with a comment explaining the extra 
diff vs native i386 Linux version of the same file.
 -- Keir


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