Re: [Xen-devel] deleting mtrrs in dom0

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> I thought the MTRRs have been set by the BIOS, not Xen.
Xen propagates the CPU0 MTRR values to all other CPUs. Not all BIOSes 
do that properly. Linux does the same, when it is booted natively.
> The MTRRs are not set to my satisfaction, that's why I'd like to change
> them.
Hmmm... can you try changing init_table() in 
arch/xen/i386/kernel/cpu/mtrr/main.c to initialise the usage_table 
counts to 1 instead of 0? I think that'll fix it for you and matches 
how native Linux initialises the table.
> Obviously, Linux has code to do that -- under Xen it unfortunately
> only sees a subset of the CPUs, though.
You need to lock out all other CPU activity while you reprogram MTRRs 
across all CPUs. Obviously Linux cannot do that unaided if Xen is 
running underneath it.
I think the current approach is the correct one, but I was probably 
trying to be too clever when defining the interface to Xen -- we'll 
probably end up dumbing it down, and only allow domain0 to do MTRR 
updates. We can always define an interface thru domain0 for other 
driver domains to declare memory types if we feel the need.
If you can check that modifying initialisation of usage_table[] fixes 
your problem, I'll do a cleanup and simplification of the MTRR code.
 -- Keir



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