[PATCH v2] powerpc/book3s/mm: Update Oops message to print the correct translation in use

[Michael Ellerman]

"Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> writes:

> Avoids confusion when printing Oops message like below
>
>  Faulting instruction address: 0xc00000000008bdb4
>  Oops: Kernel access of bad area, sig: 11 [#1]
>  LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV
>
> This was because we never clear the MMU_FTR_HPTE_TABLE feature flag
> even if we run with radix translation. It was discussed that we should
> look at this feature flag as an indication of the capability to run
> hash translation and we should not clear the flag even if we run in
> radix translation. All the code paths check for radix_enabled() check and
> if found true consider we are running with radix translation. Follow the
> same sequence for finding the MMU translation string to be used in Oops
> message.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>
> Changes from V1:
> * Don't clear the HPTE feature flag.
>
>  arch/powerpc/kernel/traps.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 11caa0291254..b181d6860f28 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -250,15 +250,22 @@ static void oops_end(unsigned long flags, struct pt_regs *regs,
>  }
>  NOKPROBE_SYMBOL(oops_end);
>  
> +static char *get_mmu_str(void)
> +{
> +	if (early_radix_enabled())
> +		return " MMU=Radix";
> +	if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
> +		return " MMU=Hash";
> +	return "";
> +}

We don't change MMU once we're up, so just do this logic once and stash
it into a static string, rather than rechecking on every oops.

cheers

>  static int __die(const char *str, struct pt_regs *regs, long err)
>  {
>  	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
>  
> -	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s%s %s\n",
> +	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
>  	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
> -	       PAGE_SIZE / 1024,
> -	       early_radix_enabled() ? " MMU=Radix" : "",
> -	       early_mmu_has_feature(MMU_FTR_HPTE_TABLE) ? " MMU=Hash" : "",
> +	       PAGE_SIZE / 1024, get_mmu_str(),
>  	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
>  	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
>  	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
> -- 
> 2.21.0