[Qemu-devel] [PATCH 1/7] kvm: remove the hack "#if defined CONFIG_KVM || !defined NEED_CPU_H"

[Xuebing Wang]

There is no direct relevance between CONFIG_KVM and NEED_CPU_H. Thus logic of
why using "#if defined CONFIG_KVM || !defined NEED_CPU_H" is hard to explain
and hard to understand.

The root cause is that we can not *always* get correct CONFIG_KVM, because:
-   CONFIG_KVM is defined in [*-softmmu | *-linux-user]/config-target.h
-   The "common" code outside folder [*-softmmu | *-linux-user] (in build time)
    can NOT include config-target.h and can NOT *always* have valid CONFIG_KVM.

By removing "#if defined CONFIG_KVM || !defined NEED_CPU_H", we completely rely
on runtime value.

Advantage of applying this patch is: logic is clear
Disadvantage is: binary code for non-CONFIG_KVM target is bigger
                 (like sh4-softmmu or *-linux-user)
-   kvm_enabled() is always runtime (kvm_allowed), and compiler won't optimize
    if ( kvm_enabled() ) { ... } type of code.
-   Before the patch, for condition (!CONFIG_KVM && NEED_CPU_H), above example
    is preprocessed to be if (0) { ... } and then optimized

>From another perspective to explain why this patch does not cause troubles.

1) Before this patch, true value table:
--------------------------------------------------------------------------
kvm_enabled = runtime value?  | CONFIG_KVM defined? | NEED_CPU_H defined? |
              kvm_allowed     |                     |                     |
kvm_irqchip_in_kernel         |                     |                     |
... for the rest 7 defines    |                     |                     |
--------------------------------------------------------------------------
     runtime value            |         Y           |          Y          |
     runtime value            |         Y           |          N          |
(a)  const  (0/false)         |         N           |          Y          |
     runtime value            |         N           |          N          |
--------------------------------------------------------------------------

2) After this patch, true value table:
--------------------------------------------------------------------------
kvm_enabled = runtime value?  | CONFIG_KVM defined? | NEED_CPU_H defined? |
... for the rest 8 defines    |                     |                     |
--------------------------------------------------------------------------
     runtime value            |         Y           |          Y          |
     runtime value            |         Y           |          N          |
(b)  runtime value (0/false)  |         N           |          Y          |
     runtime value            |         N           |          N          |
--------------------------------------------------------------------------

-   Logic of runtime value kvm_allowed is:
    ( (kvm_available() in arch_init.c) &&
      ((-machine accel=kvm) || (-enable-kvm) in runtime) )
-   If CONFIG_KVM not defined, kvm_available() is always returns 0
-   Thus for (b), runtime is always 0
-   (b) is identical to (a)
-   result of after patch is identical to before patch

Signed-off-by: Xuebing Wang <address@hidden>
---
 include/sysemu/kvm.h |   13 -------------
 1 file changed, 13 deletions(-)

diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index a02d67c..1829206 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -49,7 +49,6 @@ extern bool kvm_gsi_routing_allowed;
 extern bool kvm_gsi_direct_mapping;
 extern bool kvm_readonly_mem_allowed;
 
-#if defined CONFIG_KVM || !defined NEED_CPU_H
 #define kvm_enabled()           (kvm_allowed)
 /**
  * kvm_irqchip_in_kernel:
@@ -123,18 +122,6 @@ extern bool kvm_readonly_mem_allowed;
  */
 #define kvm_readonly_mem_enabled() (kvm_readonly_mem_allowed)
 
-#else
-#define kvm_enabled()           (0)
-#define kvm_irqchip_in_kernel() (false)
-#define kvm_async_interrupts_enabled() (false)
-#define kvm_halt_in_kernel() (false)
-#define kvm_irqfds_enabled() (false)
-#define kvm_msi_via_irqfd_enabled() (false)
-#define kvm_gsi_routing_allowed() (false)
-#define kvm_gsi_direct_mapping() (false)
-#define kvm_readonly_mem_enabled() (false)
-#endif
-
 struct kvm_run;
 struct kvm_lapic_state;
 
-- 
1.7.9.5