Subject: Re: [RFCv2 4/9] arch/powerpc: Clean up memory hotplug failure paths

From: Nathan Fontenot <[email-masked]>
Date: Tue, 2 Feb 2016 09:04:23 -0600

On 01/28/2016 11:23 PM, David Gibson wrote:
> This makes a number of cleanups to handling of mapping failures during
> memory hotplug on Power:
> 
> For errors creating the linear mapping for the hot-added region:
>   * This is now reported with EFAULT which is more appropriate than the
>     previous EINVAL (the failure is unlikely to be related to the
>     function's parameters)
>   * An error in this path now prints a warning message, rather than just
>     silently failing to add the extra memory.
>   * Previously a failure here could result in the region being partially
>     mapped.  We now clean up any partial mapping before failing.
> 
> For errors creating the vmemmap for the hot-added region:
>    * This is now reported with EFAULT instead of causing a BUG() - this
>      could happen for external reason (e.g. full hash table) so it's better
>      to handle this non-fatally
>    * An error message is also printed, so the failure won't be silent
>    * As above a failure could cause a partially mapped region, we now
>      clean this up.
> 
> Signed-off-by: David Gibson <[email-masked]>
> ---
>  arch/powerpc/mm/hash_utils_64.c | 13 ++++++++++---
>  arch/powerpc/mm/init_64.c       | 38 ++++++++++++++++++++++++++------------
>  arch/powerpc/mm/mem.c           | 10 ++++++++--
>  3 files changed, 44 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 0737eae..e88a86e 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -635,9 +635,16 @@ static unsigned long __init htab_get_table_size(void)
>  #ifdef CONFIG_MEMORY_HOTPLUG
>  int create_section_mapping(unsigned long start, unsigned long end)
>  {
> -	return htab_bolt_mapping(start, end, __pa(start),
> -				 pgprot_val(PAGE_KERNEL), mmu_linear_psize,
> -				 mmu_kernel_ssize);
> +	int rc = htab_bolt_mapping(start, end, __pa(start),
> +				   pgprot_val(PAGE_KERNEL), mmu_linear_psize,
> +				   mmu_kernel_ssize);
> +
> +	if (rc < 0) {
> +		int rc2 = htab_remove_mapping(start, end, mmu_linear_psize,
> +					      mmu_kernel_ssize);
> +		BUG_ON(rc2 && (rc2 != -ENOENT));
> +	}
> +	return rc;
>  }
>  

<-- snip -->

>  #ifdef CONFIG_MEMORY_HOTPLUG
> @@ -217,15 +219,20 @@ static void vmemmap_remove_mapping(unsigned long start,
>  }
>  #endif
>  #else /* CONFIG_PPC_BOOK3E */
> -static void __meminit vmemmap_create_mapping(unsigned long start,
> -					     unsigned long page_size,
> -					     unsigned long phys)
> +static int __meminit vmemmap_create_mapping(unsigned long start,
> +					    unsigned long page_size,
> +					    unsigned long phys)
>  {
> -	int  mapped = htab_bolt_mapping(start, start + page_size, phys,
> -					pgprot_val(PAGE_KERNEL),
> -					mmu_vmemmap_psize,
> -					mmu_kernel_ssize);
> -	BUG_ON(mapped < 0);
> +	int rc = htab_bolt_mapping(start, start + page_size, phys,
> +				   pgprot_val(PAGE_KERNEL),
> +				   mmu_vmemmap_psize, mmu_kernel_ssize);
> +	if (rc < 0) {
> +		int rc2 = htab_remove_mapping(start, start + page_size,
> +					      mmu_vmemmap_psize,
> +					      mmu_kernel_ssize);
> +		BUG_ON(rc2 && (rc2 != -ENOENT));
> +	}
> +	return rc;
>  }
>  

If I'm reading this correctly it appears that create_section_mapping() and
vmemmap_create_mapping() for !PPC_BOOK3E are identical. Any reason to not
have one routine, perhaps just have vmemmap_create_mapping() just call
create_section_mapping()?

-Nathan