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Re: [libvirt] [PATCH qom-cpu 2/7] target-i386: Don't set any KVM flag by default if KVM is disabled



On Wed, Jan 09, 2013 at 10:46:12AM +0100, Igor Mammedov wrote:
> On Mon,  7 Jan 2013 16:20:43 -0200
> Eduardo Habkost <ehabkost redhat com> wrote:
> 
> > This is a cleanup that tries to solve two small issues:
> > 
> >  - We don't need a separate kvm_pv_eoi_features variable just to keep a
> >    constant calculated at compile-time, and this style would require
> >    adding a separate variable (that's declared twice because of the
> >    CONFIG_KVM ifdef) for each feature that's going to be enabled/disable
> >    by machine-type compat code.
> >  - The pc-1.3 code is setting the kvm_pv_eoi flag on cpuid_kvm_features
> >    even when KVM is disabled at runtime. This small incosistency in
> >    the cpuid_kvm_features field isn't a problem today because
> >    cpuid_kvm_features is ignored by the TCG code, but it may cause
> >    unexpected problems later when refactoring the CPUID handling code.
> > 
> > This patch eliminates the kvm_pv_eoi_features variable and simply uses
> > kvm_enabled() inside the enable_kvm_pv_eoi() compat function, so it
> > enables kvm_pv_eoi only if KVM is enabled. I believe this makes the
> > behavior of enable_kvm_pv_eoi() clearer and easier to understand.
> 
> Subj doesn't match what patch actually does.
> Have you meant "Don't set kvm_pv_eoi flag by default if KVM is disabled"?
> Although "eliminate kvm_pv_eoi_features variable" might better describe what
> patch is doing.


True. The other flags in kvm_default_features may be already set and
will be copied to cpuid_kvm_features even if kvm_enabled() is false.

I had a previous version of this patch that also changed the code using
kvm_default_features to check kvm_enabled(), but I removed that part and
kept only the kvm_pv_eoi_features variable removal.

Andreas, please ignore this patch (it is not necessary anymore as this
series doesn't include machine-type compatibility code for kvm_mmu).
Patches 2-7 don't depend on this patch and should apply cleanly without
it.

I will send a new version later, probably with a separate patch to
ignore kvm_default_features if kvm_enabled() is false (so there's no
need to even check kvm_enabled() inside enable_kvm_pv_eoi()).

> 
> > 
> > Signed-off-by: Eduardo Habkost <ehabkost redhat com>
> > ---
> > Cc: kvm vger kernel org
> > Cc: Michael S. Tsirkin <mst redhat com>
> > Cc: Gleb Natapov <gleb redhat com>
> > Cc: Marcelo Tosatti <mtosatti redhat com>
> > 
> > Changes v2:
> >  - Coding style fix
> > 
> > Changes v3:
> >  - Eliminate #ifdef by using the fake KVM_FEATURE_PV_EOI #define
> > ---
> >  target-i386/cpu.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index 951e206..40400ac 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -164,15 +164,15 @@ static uint32_t kvm_default_features = (1 <<
> > KVM_FEATURE_CLOCKSOURCE) | (1 << KVM_FEATURE_ASYNC_PF) |
> >          (1 << KVM_FEATURE_STEAL_TIME) |
> >          (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
> > -static const uint32_t kvm_pv_eoi_features = (0x1 << KVM_FEATURE_PV_EOI);
> >  #else
> >  static uint32_t kvm_default_features = 0;
> > -static const uint32_t kvm_pv_eoi_features = 0;
> >  #endif
> >  
> >  void enable_kvm_pv_eoi(void)
> >  {
> > -    kvm_default_features |= kvm_pv_eoi_features;
> > +    if (kvm_enabled()) {
> > +        kvm_default_features |= (1UL << KVM_FEATURE_PV_EOI);
> > +    }
> >  }
> >  
> >  void host_cpuid(uint32_t function, uint32_t count,
> 

-- 
Eduardo


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