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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.03.14 at 11:39, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2014-03-19 at 10:06 +0000, Jan Beulich wrote:
>> >>> On 19.03.14 at 10:52, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
>> > On Wed, 2014-03-19 at 09:32 +0000, Jan Beulich wrote:
>> >> >>> On 19.03.14 at 10:27, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 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@xxxxxxxxxx>
>> >> >> ---
>> >> >>  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.
>> > 
>> > Is it 0x100 or 0x1000 increments? I thought it was 0x100, in which case
>> > shouldn't the mask be 0xfffff000?
>> 
>> It's 0x100 increments, but that doesn't relate to the mask to be
>> applied here - major groups appear to be using 64k increments
>> (0000 - basic, 4000 - hypervisor, 8000 - extended, 8086 -
>> Transmeta, C000 - VIA/Cyrix, and I guess there are others I
>> don't know about). I don't think I've seen this publicly/formally
>> documented so far.
> 
> OK, that makes sense from a major group perspective.
> 
> But I think the "first minor group" of hypervisor nodes at 0x40000000
> stops at 0x40010000, at least implicitly due to the existing code in e.g
> unmodified_drivers/linux-2.6/platform-pci/platform-pci.c and
> tools/misc/xen-detect.c. I don't think it is out of the question that we
> might want to put other stuff at e.g. 0x40020000 (or at least we should
> retain the option).

So that means you advocate for shrinking the number of significant
bits checked for. Question then is by how much - perhaps we should
then consider the whole range 40000000-7FFFFFFF as hypervisor
reserved?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel