Patchwork [1/2] sparc64: Implement local_irq_save_nmi().

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Submitter David Miller
Date April 6, 2010, 11:39 p.m.
Message ID <20100406.163955.28809295.davem@davemloft.net>
Download mbox | patch
Permalink /patch/49555/
State RFC
Delegated to: David Miller
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Comments

David Miller - April 6, 2010, 11:39 p.m.
It disables up to PIL_NMI instead of just PIL_NORMAL_MAX.

Signed-off-by: David S. Miller <davem@davemloft.net>

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Peter Zijlstra - April 7, 2010, 6:52 a.m.
On Tue, 2010-04-06 at 16:39 -0700, David Miller wrote:
> It disables up to PIL_NMI instead of just PIL_NORMAL_MAX.
> 
> Signed-off-by: David S. Miller <davem@davemloft.net>
> 
> diff --git a/arch/sparc/include/asm/irqflags_64.h b/arch/sparc/include/asm/irqflags_64.h
> index 8b49bf9..fa1e00e 100644
> --- a/arch/sparc/include/asm/irqflags_64.h
> +++ b/arch/sparc/include/asm/irqflags_64.h
> @@ -49,6 +49,16 @@ static inline void raw_local_irq_disable(void)
>  	);
>  }
>  
> +static inline void raw_local_irq_disable_nmi(void)
> +{
> +	__asm__ __volatile__(
> +		"wrpr	%0, %%pil"
> +		: /* no outputs */
> +		: "i" (PIL_NMI)
> +		: "memory"
> +	);
> +}
> +

Isn't this wrong when used from !NMI context?

Should this thing do something like:

  if (rdpr() < PIL_NORMAL_MAX)
    wrpr(PIL_NORMAL_MAX);

so that it only disables IRQs, but doesn't enable NMIs.
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David Miller - April 7, 2010, 7:06 a.m.
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 07 Apr 2010 08:52:26 +0200

> On Tue, 2010-04-06 at 16:39 -0700, David Miller wrote:
>> @@ -49,6 +49,16 @@ static inline void raw_local_irq_disable(void)
>>  	);
>>  }
>>  
>> +static inline void raw_local_irq_disable_nmi(void)
>> +{
>> +	__asm__ __volatile__(
>> +		"wrpr	%0, %%pil"
>> +		: /* no outputs */
>> +		: "i" (PIL_NMI)
>> +		: "memory"
>> +	);
>> +}
>> +
> 
> Isn't this wrong when used from !NMI context?
> 
> Should this thing do something like:
> 
>   if (rdpr() < PIL_NORMAL_MAX)
>     wrpr(PIL_NORMAL_MAX);
> 
> so that it only disables IRQs, but doesn't enable NMIs.

It's immaterial, local_irq_restore() will do the right thing,
and it's ok to disable NMIs in these few cases I think.

I desperately want to avoid that "test and maybe change the
value %pil value we write" business, and honestly that's
the whole point of this exercise.
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Peter Zijlstra - April 7, 2010, 7:24 a.m.
On Wed, 2010-04-07 at 00:06 -0700, David Miller wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed, 07 Apr 2010 08:52:26 +0200
> 
> > On Tue, 2010-04-06 at 16:39 -0700, David Miller wrote:
> >> @@ -49,6 +49,16 @@ static inline void raw_local_irq_disable(void)
> >>  	);
> >>  }
> >>  
> >> +static inline void raw_local_irq_disable_nmi(void)
> >> +{
> >> +	__asm__ __volatile__(
> >> +		"wrpr	%0, %%pil"
> >> +		: /* no outputs */
> >> +		: "i" (PIL_NMI)
> >> +		: "memory"
> >> +	);
> >> +}
> >> +
> > 
> > Isn't this wrong when used from !NMI context?
> > 
> > Should this thing do something like:
> > 
> >   if (rdpr() < PIL_NORMAL_MAX)
> >     wrpr(PIL_NORMAL_MAX);
> > 
> > so that it only disables IRQs, but doesn't enable NMIs.
> 
> It's immaterial, local_irq_restore() will do the right thing,
> and it's ok to disable NMIs in these few cases I think.
> 
> I desperately want to avoid that "test and maybe change the
> value %pil value we write" business, and honestly that's
> the whole point of this exercise.

Sure, its your architecture.. but could you explain why you're trying to
avoid that compare so desperately, the local_irq_save_nmi() calls are
few so surely they could carry that overhead.

Also, doesn't __raw_local_irq_save_flags() already do the read? So its
really just the compare that's gone missing.
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Patch

diff --git a/arch/sparc/include/asm/irqflags_64.h b/arch/sparc/include/asm/irqflags_64.h
index 8b49bf9..fa1e00e 100644
--- a/arch/sparc/include/asm/irqflags_64.h
+++ b/arch/sparc/include/asm/irqflags_64.h
@@ -49,6 +49,16 @@  static inline void raw_local_irq_disable(void)
 	);
 }
 
+static inline void raw_local_irq_disable_nmi(void)
+{
+	__asm__ __volatile__(
+		"wrpr	%0, %%pil"
+		: /* no outputs */
+		: "i" (PIL_NMI)
+		: "memory"
+	);
+}
+
 static inline void raw_local_irq_enable(void)
 {
 	__asm__ __volatile__(
@@ -83,9 +93,28 @@  static inline unsigned long __raw_local_irq_save(void)
 	return flags;
 }
 
+static inline unsigned long __raw_local_irq_save_nmi(void)
+{
+	unsigned long flags = __raw_local_save_flags();
+
+	raw_local_irq_disable_nmi();
+
+	return flags;
+}
+
 #define raw_local_irq_save(flags) \
 		do { (flags) = __raw_local_irq_save(); } while (0)
 
+#define raw_local_irq_save_nmi(flags) \
+		do { (flags) = __raw_local_irq_save_nmi(); } while (0)
+
+#define local_irq_save_nmi(flags) 			\
+	do {						\
+		 typecheck(unsigned long, flags);	\
+		 raw_local_irq_save_nmi(flags);		\
+		 trace_hardirqs_off();			\
+	} while (0)
+
 #endif /* (__ASSEMBLY__) */
 
 #endif /* !(_ASM_IRQFLAGS_H) */