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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

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@oracle.com>
>>> 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.


-boris