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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Oct 09, 2012 at 02:18:05PM -0300, Marcelo Tosatti wrote:
> 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.

Err, meant via properties. Point is, why have VMWare CPUID
configuration as data, if there are reasons to believe code 
is a better fit (code as in current Hyper-V implementation).

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