Subject: [PATCH] ARM: Do not run dummy_flush_tlb_a15_erratum() on non-Cortex-A15

From: [email-masked] (Catalin Marinas)
Date: Tue, 23 Jul 2013 12:07:12 +0100

On Tue, Jul 23, 2013 at 09:13:58AM +0100, Roger Quadros wrote:
> On 07/23/2013 08:19 AM, Fabio Estevam wrote:
> > From: Fabio Estevam <[email-masked]>
> > 
> > Commit 93dc688 (ARM: 7684/1: errata: Workaround for Cortex-A15 erratum 798181 
> > (TLBI/DSB operations)) causes the following undefined instruction error on a
> > mx53 (Cortex-A8):
> > 
> > Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
> > CPU: 0 PID: 275 Comm: modprobe Not tainted 3.11.0-rc2-next-20130722-00009-g9b0f371 #881
> > task: df46cc00 ti: df48e000 task.ti: df48e000
> > PC is at check_and_switch_context+0x17c/0x4d0
> > LR is at check_and_switch_context+0xdc/0x4d0
> > 
> > This problem happens because check_and_switch_context() calls 
> > dummy_flush_tlb_a15_erratum() without checking if we are really running on a 
> > Cortex-A15 or not. 
> > 
> > To avoid this issue, always check if we are running on a Cortex-A15 or not 
> > (via erratum_a15_798181()) inside dummy_flush_tlb_a15_erratum(), so that we do 
> > not need to keep doing the same check in all occurrences of 
> > dummy_flush_tlb_a15_erratum().
> > 
> > Signed-off-by: Fabio Estevam <[email-masked]>
> > ---
> >  arch/arm/include/asm/tlbflush.h | 18 ++++++++++++++++++
> >  arch/arm/kernel/smp_tlb.c       | 23 -----------------------
> >  2 files changed, 18 insertions(+), 23 deletions(-)
> > 
> > diff --git a/arch/arm/include/asm/tlbflush.h b/arch/arm/include/asm/tlbflush.h
> > index fdbb9e3..2478b6f 100644
> > --- a/arch/arm/include/asm/tlbflush.h
> > +++ b/arch/arm/include/asm/tlbflush.h
> > @@ -443,9 +443,22 @@ static inline void local_flush_bp_all(void)
> >  		isb();
> >  }
> >  
> > +#include <asm/cputype.h>
> >  #ifdef CONFIG_ARM_ERRATA_798181
> > +static inline int erratum_a15_798181(void)
> > +{
> > +	unsigned int midr = read_cpuid_id();
> > +
> > +	/* Cortex-A15 r0p0..r3p2 affected */
> > +	if ((midr & 0xff0ffff0) != 0x410fc0f0 || midr > 0x413fc0f2)
> > +		return 0;
> > +	return 1;
> > +}
> > +
> >  static inline void dummy_flush_tlb_a15_erratum(void)
> >  {
> > +	if (!erratum_a15_798181())
> > +		return;
> >  	/*
> >  	 * Dummy TLBIMVAIS. Using the unmapped address 0 and ASID 0.
> >  	 */
> > @@ -453,6 +466,11 @@ static inline void dummy_flush_tlb_a15_erratum(void)
> >  	dsb();
> >  }
> >  #else
> > +static inline int erratum_a15_798181(void)
> > +{
> > +	return 0;
> > +}
> > +
> >  static inline void dummy_flush_tlb_a15_erratum(void)
> >  {
> >  }
> > diff --git a/arch/arm/kernel/smp_tlb.c b/arch/arm/kernel/smp_tlb.c
> > index a98b62d..29e9038 100644
> > --- a/arch/arm/kernel/smp_tlb.c
> > +++ b/arch/arm/kernel/smp_tlb.c
> > @@ -70,23 +70,6 @@ static inline void ipi_flush_bp_all(void *ignored)
> >  	local_flush_bp_all();
> >  }
> >  
> > -#ifdef CONFIG_ARM_ERRATA_798181
> > -static int erratum_a15_798181(void)
> > -{
> > -	unsigned int midr = read_cpuid_id();
> > -
> > -	/* Cortex-A15 r0p0..r3p2 affected */
> > -	if ((midr & 0xff0ffff0) != 0x410fc0f0 || midr > 0x413fc0f2)
> > -		return 0;
> > -	return 1;
> > -}
> > -#else
> > -static int erratum_a15_798181(void)
> > -{
> > -	return 0;
> > -}
> > -#endif
> > -
> >  static void ipi_flush_tlb_a15_erratum(void *arg)
> >  {
> >  	dmb();
> > @@ -94,9 +77,6 @@ static void ipi_flush_tlb_a15_erratum(void *arg)
> >  
> >  static void broadcast_tlb_a15_erratum(void)
> >  {
> > -	if (!erratum_a15_798181())
> > -		return;
> > -
> 
> Removing this if statement will cause "ipi_flush_tlb_a15_erratum" to be called
> on non A15 platforms. So I would just keep it to be safe.

I agree, this must stay. But to avoid erratum_a15_798181() called too
many times, I would rather add the condition in
check_and_switch_context() where dummy_flush_tlb_a15_erratum() is
called.

An alternative (and Will has a patch) is to always use
cpumask_setall(&tlb_flush_pending) in flush_context() and the
check_and_switch_context() function doesn't need to guarantee any
broadcast. In this case we simply remove dummy_flush_tlb_a15_erratum()
in context.c (but I guess for cc: stable we can use an 'if (erratum...)').

-- 
Catalin