Re: [PATCH v6 05/16] target-i386: Use Hypervisor level in -machine pc,accel=kvm.

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Sep 24, 2012 at 10:32:07AM -0400, Don Slutz wrote:
> Also known as Paravirtualization level.
> 
> This change is based on:
> 
> Microsoft Hypervisor CPUID Leaves:
>   http://msdn.microsoft.com/en-us/library/windows/hardware/ff542428%28v=vs.85%29.aspx
> 
> Linux kernel change starts with:
>   http://fixunix.com/kernel/538707-use-cpuid-communicate-hypervisor.html
> Also:
>   http://lkml.indiana.edu/hypermail/linux/kernel/1205.0/00100.html
> 
> VMware documention on CPUIDs (Mechanisms to determine if software is
> running in a VMware virtual machine):
>   http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009458
> 
> QEMU knows this is KVM_CPUID_SIGNATURE (0x40000000).
> 
> Signed-off-by: Don Slutz <Don@CloudSwitch.com>
> ---
>  target-i386/kvm.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 895d848..8462c75 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -389,12 +389,12 @@ int kvm_arch_init_vcpu(CPUX86State *env)
>      c = &cpuid_data.entries[cpuid_i++];
>      memset(c, 0, sizeof(*c));
>      c->function = KVM_CPUID_SIGNATURE
> -    if (!hyperv_enabled()) {
> +    if (!env->cpuid_hv_level_set) {
>          memcpy(signature, "KVMKVMKVM\0\0\0", 12);
>          c->eax = 0;
>      } else {
>          memcpy(signature, "Microsoft Hv", 12);
> -        c->eax = HYPERV_CPUID_MIN;
> +        c->eax = env->cpuid_hv_level;

This breaks hyperv_enabled() checks. 

Don, are you certain it is worthwhile to make this configurable? 
Can you explain why, under your scenario, it is worthwhile?

Because these are separate problems:

- "Fake" VMWare hypervisor  (which seems to be your main goal).
- Make CPUID HV leafs configurable via command line.

My point is that the CPUIDs must be carefully constructed, 
that i miss the point why making them configurable is 
desired.