Re: [v1][PATCH 1/1] KVM: PPC: disable preemption when using hard_irq_disable()

["tiejun.chen" <tiejun.chen@windriver.com>]

On 07/12/2013 11:57 AM, Benjamin Herrenschmidt wrote:
> On Fri, 2013-07-12 at 10:13 +0800, tiejun.chen wrote:
>>> #define hard_irq_disable()    do {                    \
>>>        u8 _was_enabled = get_paca()->soft_enabled;     \
>>
>> Current problem I met is issued from the above line.
>>
>>>        __hard_irq_disable();                           \
>>> -     get_paca()->soft_enabled = 0;                   \
>>
>> Not here.
>>
>> If I'm misunderstanding what you guys means, please correct me since this is a
>> long discussion thread. I have to reread that carefully.
>
> Then make it
> 	u8 _was_enabled;
> 	__hard_irq_disable();
> 	was_enabled = local_paca->....
>
> Once you have hard disabled, using local_paca directly *should* be safe
> (minus that gcc problem I mentioned).

Is the following fine?

powerpc: to access local paca after hard irq disabled

We can access paca directly after hard interrupt disabled, and
this can avoid accessing wrong paca when using get_paca() in
preempt case.

Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
  arch/powerpc/include/asm/hw_irq.h |    7 ++++---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index ba713f1..10be1dd 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -96,10 +96,11 @@ static inline bool arch_irqs_disabled(void)
  #endif

  #define hard_irq_disable()     do {                    \
-       u8 _was_enabled = get_paca()->soft_enabled;     \
+       u8 _was_enabled;                                \
         __hard_irq_disable();                           \
-       get_paca()->soft_enabled = 0;                   \
-       get_paca()->irq_happened |= PACA_IRQ_HARD_DIS;  \
+       _was_enabled = local_paca->soft_enabled;        \
+       local_paca->soft_enabled = 0;                   \
+       local_paca->irq_happened |= PACA_IRQ_HARD_DIS;  \
         if (_was_enabled)                               \
                 trace_hardirqs_off();                   \
  } while(0)
-- 
1.7.9.5


Or what about that change to call SOFT_DISABLE_INTS only in KVM scenario? Which 
better?

Then I can send to review?

Thanks,

Tiejun