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

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Submitter Eduardo Habkost
Date Jan. 7, 2013, 6:20 p.m.
Message ID <1357582848-16575-3-git-send-email-ehabkost@redhat.com>
Download mbox | patch
Permalink /patch/210110/
State New
Headers show

Comments

Eduardo Habkost - Jan. 7, 2013, 6:20 p.m.
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.

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(-)
Igor Mammedov - Jan. 9, 2013, 9:46 a.m.
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.

> 
> 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 Habkost - Jan. 9, 2013, 11:41 a.m.
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 Habkost - Jan. 9, 2013, 11:44 a.m.
On Wed, Jan 09, 2013 at 09:41:37AM -0200, Eduardo Habkost wrote:
[...]
> 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 mean: patches 1 and 3-7 don't depend on this patch and can be applied
cleanly without it.

Patch

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,