Re: [PATCH v5 1/4] xen/libxc: Allow changes to hypervisor CPUID leaf from config file

["Jan Beulich" <JBeulich@suse.com>]

>>> On 19.03.14 at 10:27, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> On Tue, 2014-03-18 at 20:58 -0400, 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 (but for now only 0x40000000 is allowed).
>> 
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>  tools/libxc/xc_cpuid_x86.c   |   71 
> ++++++++++++++++++++++++++++++++++++++++--
>>  xen/arch/x86/domain.c        |   19 +++++++++--
>>  xen/arch/x86/traps.c         |    3 ++
>>  xen/include/asm-x86/domain.h |    7 +++++
>>  4 files changed, 95 insertions(+), 5 deletions(-)
>> 
>> diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
>> index bbbf9b8..5501d5b 100644
>> --- a/tools/libxc/xc_cpuid_x86.c
>> +++ b/tools/libxc/xc_cpuid_x86.c
>> @@ -33,6 +33,8 @@
>>  #define DEF_MAX_INTELEXT  0x80000008u
>>  #define DEF_MAX_AMDEXT    0x8000001cu
>>  
>> +#define IS_HYPERVISOR_LEAF(idx) (((idx) & 0xffff0000) == 0x40000000)
> 
> Not idx == 0x40000000?
> 
> Also as I think Jan said before if viridian support is enabled then the
> Xen leaves may be elsewhere (at 0x100 increments above that address
> IIRC).

But that's exactly why the low 16 bits should be masked off in
above comparison.

Jan