[XenPPC] Next profiling clarification question

[Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>]

Hi,
I have one more questions regarding the oprofile extension to work in 
xenppc guests.
The plain linux implementation sets !always! the vector for the 
performance interrupt 0xf00 to the function 
"performance_monitor_exception" in head32.S/head64.S. Depending on 
wether linux starts profiling this function is set to a dummy or the 
"real" handler of e.g. oprofile.
Now in the virtualized environment each guest set's its own interrupt 
handler for 0xf00 (Performance monitor interrupt). Because we are 
running with LPSE[1]=0 as Jimi wrote before the performance interrupt 
while a Dom is running should be handled from the domain because nothing 
sets MSR[HV] to 1.
My question is now if the address translation & virtualization ensures 
that each perf interrupt will be a) served by the right function adress 
and b) in the domain. Maybe there is some exclusive part involved and 
the different writes of the 0xf00 vector may overwrite each other or 
something similar - that's why I want to ask to be sure.
Example of a system with two DomU guests that enabled the performance 
counters.
Running:
Xen
0xf00 -> undef?
Dom0
0xf00 -> default_pmc_irq
DomU1
0xf00 ->    pmc_irq_handler1
DomU2
0xf00 ->    pmc_irq_handler2

If now interrupts occur in all those domains (I know we don't set it up 
but hypothetical) will the system behave the expected way:
Occur in:
Xen -> skip
Dom0 -> call default_pmc_irq in Dom0
DomU1 -> call pmc_irq_handler1
DomU2 -> call pmc_irq_handler1

--

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt@xxxxxxxxxxxxxxxxxxx
Ehrhardt@xxxxxxxxxx

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