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

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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