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

From: [email-masked] (Roger Quadros)
Date: Tue, 23 Jul 2013 11:13:58 +0300

Hi Fabio,

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.

>  	dummy_flush_tlb_a15_erratum();
>  	smp_call_function(ipi_flush_tlb_a15_erratum, NULL, 1);
>  }
> @@ -106,9 +86,6 @@ static void broadcast_tlb_mm_a15_erratum(struct mm_struct *mm)
>  	int this_cpu;
>  	cpumask_t mask = { CPU_BITS_NONE };
>  
> -	if (!erratum_a15_798181())
> -		return;
> -

same here.
>  	dummy_flush_tlb_a15_erratum();
>  	this_cpu = get_cpu();
>  	a15_erratum_get_cpumask(this_cpu, mm, &mask);
> 

cheers,
-roger