Re: [Qemu-devel] [PATCH 2/2] target-i386: kvm: enable all supported KVM features for -cpu host

[Eduardo Habkost]

On Wed, Jan 02, 2013 at 03:52:45PM +0100, Igor Mammedov wrote:
> On Fri, 28 Dec 2012 16:37:34 -0200
> Eduardo Habkost <address@hidden> wrote:
> 
> > When using -cpu host, we don't need to use the kvm_default_features
> > variable, as the user is explicitly asking QEMU to enable all feature
> > supported by the host.
> > 
> > This changes the kvm_cpu_fill_host() code to use GET_SUPPORTED_CPUID to
> > initialize the kvm_features field, so we get all host KVM features
> > enabled.
> 
> 1_2 and 1_3 compat machines diff on pv_eoi flag, with this patch 1_2 might
> have it set.
> Is it ok from compat machines pov?

-cpu host is completely dependent on host hardware and kernel version,
there are no compatibility expectations.

> 
> > 
> > This will also allow use to properly check/enforce KVM features inside
> > kvm_check_features_against_host() later. For example, we will be able to
> > make this:
> > 
> >   $ qemu-system-x86_64 -cpu ...,+kvm_pv_eoi,enforce
> > 
> > refuse to start if kvm_pv_eoi is not supported by the host (after we fix
> > kvm_check_features_against_host() to check KVM flags as well).
> It would be nice to have kvm_check_features_against_host() patch in this
> series to verify that this patch and previous patch works as expected.

The kvm_check_features_against_host() change would be a user-visible
behavior change, and I wanted to keep the changes minimal by now. (the
main reason I submitted this earlier is to make it easier to clean up
the init code for CPU subclasses)

I was planning to introduce those behavior changes only after
introducing the feature-word array, so the kvm_check_features_against_host()
code can become simpler and easier to review (instead of adding 4
additional items to the messy struct model_features_t array). But if you
think we can introduce those changes now, I will be happy to send a
series that changes that code as well.

> 
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
> > ---
> >  target-i386/cpu.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index 6e2d32d..76f19f0 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -900,6 +900,8 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
> >      /* Other KVM-specific feature fields: */
> >      x86_cpu_def->svm_features =
> >                  kvm_arch_get_supported_cpuid(s, 0x8000000A, 0, R_EDX);
> > +    x86_cpu_def->kvm_features =
> > +                kvm_arch_get_supported_cpuid(s, KVM_CPUID_FEATURES, 0,
> > R_EAX); 
> >  #endif /* CONFIG_KVM */
> >  }
> 

-- 
Eduardo