kvm: Add fake KVM_FEATURE_CLOCKSOURCE_STABLE_BIT for builds without KVM

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: Don't set any KVM flag by default if KVM is disabled

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/disabled 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 inconsistency 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.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
pc: Reverse pc_init_pci() compatibility logic

Currently, the pc-1.4 machine init function enables PV EOI and then
calls the pc-1.2 machine init function. The problem with this approach
is that now we can't enable any additional compatibility code inside the
pc-1.2 init function because it would end up enabling the compatibility
behavior on pc-1.3 and pc-1.4 as well.

This reverses the logic so that the pc-1.2 machine init function will
disable PV EOI, and then call the pc-1.4 machine init function.

This way we can change older machine-types to enable compatibility
behavior, and the newer machine-types (pc-1.3, pc-q35-1.4 and
pc-i440fx-1.4) would just use the default behavior.

(This means that one nice side-effect of this change is that pc-q35-1.4
will get PV EOI enabled by default, too)

It would be interesting to eventually change pc_init_pci_no_kvmclock()
and pc_init_isa() to reuse pc_init_pci_1_2() as well (so we don't need
to duplicate compatibility code on those two functions). But this will
be probably much easier to do after we create a PCInitArgs struct for
the PC initialization arguments, and/or after we use global-properties
to implement the compatibility modes present in pc_init_pci_1_2().

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>