Pkg xen devel - Jan 2012 - Bug#649141: closed by Bastian Blank <waldi@debian.org> (no bug)

On Sun, Dec 11, 2011 at 06:03, Debian Bug Tracking System
<owner at bugs.debian.org>
> ---------- Forwarded message ----------
> From:?Bastian Blank <waldi at debian.org>
>
> This is no bug, but actually documented. You can't migrate systems to a
> cpu with lower capabilities.
Out of interest, where is this documented?

The debian examples would seem to indicate you can, by limiting the
guest CPU features:

Try zgrep cpuid /usr/share/doc/xen-utils-common/examples/*

It should also be possible to do so by masking features on the host
CPU, via kernel boot options ( see http://zhigang.org/wiki/XenCPUID )

However in 'xm dmesg' I get the following:

(XEN) Cannot set CPU feature mask on CPU#0
(XEN) Cannot set CPU feature mask on CPU#1
(XEN) Cannot set CPU feature mask on CPU#2
(XEN) Cannot set CPU feature mask on CPU#3
(XEN) Cannot set CPU feature mask on CPU#4
(XEN) Cannot set CPU feature mask on CPU#5
(XEN) Cannot set CPU feature mask on CPU#6
(XEN) Cannot set CPU feature mask on CPU#7
(XEN) Cannot set CPU feature mask on CPU#8
(XEN) Cannot set CPU feature mask on CPU#9
(XEN) Cannot set CPU feature mask on CPU#10
(XEN) Cannot set CPU feature mask on CPU#11
(XEN) Cannot set CPU feature mask on CPU#12
(XEN) Cannot set CPU feature mask on CPU#13
(XEN) Cannot set CPU feature mask on CPU#14
(XEN) Cannot set CPU feature mask on CPU#15

when trying to boot with the following options:

cpuid_mask_ecx=0x0008E3FD cpuid_mask_edx=0xBFEBFBFF

It accepts and tries to act on the mask, but does not succeed. Also
does not give indication as to why.
-- 
Marcus Furlong