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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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?

I think this should be clarified in the xen/include/public/cpuid.h
header, perhaps including this sort of macro for convenience.

Ian.


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