Re: [libvirt] [PATCH qom-cpu 01/11] target-i386: Don't set any KVM flag by default if KVM is disabled

On Mon, Jan 07, 2013 at 09:42:36AM -0200, Eduardo Habkost wrote: > On Sun, Jan 06, 2013 at 01:32:34PM +0200, Gleb Natapov wrote: > > On Fri, Jan 04, 2013 at 08:01:02PM -0200, Eduardo Habkost 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 > > > CONFIG_KVM and 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. > > > > > > Signed-off-by: Eduardo Habkost <ehabkost(a)redhat.com&gt; > > > --- > > > Cc: kvm(a)vger.kernel.org > > > Cc: Michael S. Tsirkin <mst(a)redhat.com&gt; > > > Cc: Gleb Natapov <gleb(a)redhat.com&gt; > > > Cc: Marcelo Tosatti <mtosatti(a)redhat.com&gt; > > > > > > Changes v2: > > > - Coding style fix > > > --- > > > target-i386/cpu.c | 8 +++++--- > > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c > > > index 82685dc..e6435da 100644 > > > --- a/target-i386/cpu.c > > > +++ b/target-i386/cpu.c > > > @@ -145,15 +145,17 @@ 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; > > > +#ifdef CONFIG_KVM > > You do not need ifdef here. > > We need it because KVM_FEATURE_PV_EOI is available only if CONFIG_KVM is > set. > > I could also write it as: > > if (kvm_enabled()) { > #ifdef CONFIG_KVM > kvm_default_features |= (1UL << KVM_FEATURE_PV_EOI); > #endif > } > > But I find it less readable. > > Why not define KVM_FEATURE_PV_EOI unconditionally?

> > > > > + if (kvm_enabled()) { > > > + kvm_default_features |= (1UL << KVM_FEATURE_PV_EOI); > > > + } > > > +#endif > > > } > > > > > > void host_cpuid(uint32_t function, uint32_t count, > > > -- > > > 1.7.11.7 > > > > -- > > Gleb. > > -- > Eduardo -- Gleb.