Re: [RFC] Use para_fill instead of vmi_get_function for APIC ops

From: Zachary Amsden
Date: Mon Feb 26 2007 - 19:44:16 EST


Anthony Liguori wrote:
Hi Zach,

It seems to me that the APIC paravirt_ops should be filled by para_fill() instead of vmi_get_function(). vmi_get_function() returns a nop when the relocation type is NONE. para_fill() leaves the native code in place.

The native version of the apic write ops is more or less *(APIC_BASE + reg) = value. APIC_BASE is unknown to the ROM so it's impossible to simulate this in the ROM.

This means that a ROM has no choice but to do APIC emulation (or jump through seriously hairy loops to get the APIC mapped in it's address space). Was this the intention?

No, but certainly the effect. Actually, it is very easy to get the APIC mapped in the ROM address space without jumping through seriously hairy loops - we do it today in our hypervisor.


N.B. attached patch is just to illustrate the point. Has not even been compile tested.


Patch looks good, thanks. But the whole para_fill / vmi_get_function stuff could probably be done even cleaner. It was just a helper at first to work around the awkward syntax, and it is still a bit ugly, but I haven't come up with a better solution yet, mostly because with the new inlining work Jeremy is doing, we might want to start doing selective inlining, in which case I'll have to go back over the code anyway to clean everything to get the logic right in all cases.

I assume this patch is signed-off-by you? If so, I'll add it to my patch queue.

Zach
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