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Re: [Xen-devel] [PATCH v2 1/4] xen/libxc: Allow changes to hypervisor CPUID leaf from config file

On 03/11/2014 10:26 AM, Andrew Cooper wrote:
On 11/03/14 14:07, Boris Ostrovsky wrote:
On 03/11/2014 06:10 AM, Andrew Cooper wrote:
On 11/03/14 03:54, Boris Ostrovsky wrote:
Currently only "real" cpuid leaves can be overwritten by users via
'cpuid' option in the configuration file. This patch provides
ability to
do the same for hypervisor leaves (those in the 0x40000000 range).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
How?  There is nothing stopping leaves in 0x40000000 being set in the
policy with XEN_DOMCTL_set_cpuid, but I dont see anything which plumbs
this together at the Xen level.
Right. What this patch mostly provides is ability to query the
hypervisor (via sysctl) about default values of hypervisor CPUID leaf
from userspace. We cannot use CPUID instruction here (for dom0). And
/dev/cpu/<n>/cpuid may not exist.
The XEN_FORCED_EMULATION prefix would be fine, and not require a new
custom hypercall, but only an HVM guest is going to care whether it can
find this magic leaf.

Doh! For some reasons I decided that it won't work for userland. But of course it will. Which eliminates the need for sysctl.


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