Description of problem:

(This was reported in a private email by Ian Campbell)

<<
For HVM (32 or 64 bit) virt-what returns:
# virt-what                                                                     
hyperv
xen

I disabled the Xen Viridian extensions and it returns:
# virt-what                                                                     
xen
xen-hvm

Your cpuid helper should check every 0x100 from 0x40000000
and then it will find multiple signatures on Xen when
viridian compat is enabled.
>>

Ian goes on to point to this piece of code from xendetect:

        static inline uint32_t xen_cpuid_base(void)
        {
                uint32_t base, eax, ebx, ecx, edx;
                char signature[13];

                for (base = 0x40000000; base < 0x40010000; base += 0x100) {
                        cpuid(base, &eax, &ebx, &ecx, &edx);
                        *(uint32_t *)(signature + 0) = ebx;
                        *(uint32_t *)(signature + 4) = ecx;
                        *(uint32_t *)(signature + 8) = edx;
                        signature[12] = 0;

                        if (!strcmp("XenVMMXenVMM", signature) && ((eax - base)
>= 2))
                                return base;
                }                                                               

                return 0;
        }                                                                       


Version-Release number of selected component (if applicable):

virt-what 1.7

How reproducible:

Always.

Steps to Reproduce:
1. Using upstream Xen, HVM with Viridian extensions turned on.
2. Run virt-what in the guest.
  
Actual results:

hyperv
xen

Expected results:

Something like:

xen
xen-hvm
xen-hyperv_compat

Additional info: