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[Qemu-devel] [0/3] pseries: RFC: Advertise host CPU capabilties to guest

From: David Gibson
Subject: [Qemu-devel] [0/3] pseries: RFC: Advertise host CPU capabilties to guest
Date: Fri, 30 Sep 2011 17:50:37 +1000

This series contains some patches which, when using KVM, gather
information about the capabilities of the host CPU and advertise them
to the guest system when using the pseries machine.  Specifically it
does this for whether the CPU supports VMX, VSX and/or DFP
instructions, and for the CPUs supported page sizes.

The VSX and DFP portions of this were posted earlier, and I've fixed
the minor comments which people made.  This leaves one objection from
Alex Graf, that whether the features are advertised should also depend
on the target CPU selected in qemu.  A similar objection may apply to
the pagesizes patch.  I guess the idea is to "clamp" the advertised
capabilities to those permitted by the selected target CPU, but I'm
not entirely sure what the logic here should be.

Frankly, particularly in the case of KVM Book3S-HV, I'm not terribly
convinced that attempting to make the guest CPU appear different from
the host CPU is terribly meaningful.  These patches as they stand have
the advantage that future, roughly compatible CPUs should Just Work
with these capabilities advertised in the correct cases.  Alex, can
you advise what sort of logic you'd like here.

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