Karmic/Lucid i386 virtual flavour

Andy Whitcroft apw at canonical.com
Tue Feb 9 18:20:50 UTC 2010

There has been some discussion about XEN not working with the 32bit kernels
in both Karmic and Lucid it seems that when we moved from having a server
flavour to having a generic-pae flavour in 32bit we moved from M686 to
M586 for that PAE based kernel.  XEN dom-U now does not work because
it is dependant on TSC support in the processor.  Note that the Jaunty
server flavour config was CONFIG_M686 which includes TSC automatically.
It does appear from Wikipedia that PAE support comes after TSC support in
the Pentium timeline and therefore we may well be able to enable TSC and
XEN by switching the generic-pae config over to CONFIG_M586TSC mode, as
to have PAE capabilities you must also have a TSC.  M586TSC is basically
just M586 (what we have now) plus TSC.

For TSC:
	The Time Stamp Counter is a 64-bit register present on all x86
	processors since the Pentium. It counts the number of ticks
	since reset.  Instruction RDTSC returns the TSC in EDX:EAX. Its
	opcode is 0F 31.[1] Pentium competitors such as the Cyrix 6x86
	did not always have a TSC and may consider RDTSC an illegal
	instruction. Cyrix included a Time Stamp Counter in their MII

For PAE:
	In computing, Physical Address Extension (PAE) is a feature of
	some x86 and x86-64 processors that enables the use of more than
	4 gigabytes[1] of physical memory to be used in 32-bit systems
	- given appropriate operating system support. PAE is provided
	by Intel Pentium Pro (and above) CPUs - including all later
	Pentium-series processors except the 400 MHz bus versions of the
	Pentium M, as well as by other processors such as the AMD Athlon
	and later AMD processor models with similar or more advanced
	versions of the same architecture.

I think this should be safe for Lucid, Karmic may be a little more
difficult.  I propose we make the change in Lucid and get some miles on
it in the Alphas before we decide on Karmic.



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