Re: [PATCH v3 5/6] mm: Fix memory_failure() handling of dax-namespace metadata

[David Hildenbrand]

On 13.01.21 08:35, Dan Williams wrote:
> Given 'struct dev_pagemap' spans both data pages and metadata pages be
> careful to consult the altmap if present to delineate metadata. In fact
> the pfn_first() helper already identifies the first valid data pfn, so
> export that helper for other code paths via pgmap_pfn_valid().
> 
> Other usage of get_dev_pagemap() are not a concern because those are
> operating on known data pfns having been looking up by get_user_pages().
> I.e. metadata pfns are never user mapped.
> 
> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Reported-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  include/linux/memremap.h |    6 ++++++
>  mm/memory-failure.c      |    6 ++++++
>  mm/memremap.c            |   15 +++++++++++++++
>  3 files changed, 27 insertions(+)
> 
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 79c49e7f5c30..f5b464daeeca 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -137,6 +137,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
>  void devm_memunmap_pages(struct device *dev, struct dev_pagemap *pgmap);
>  struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  		struct dev_pagemap *pgmap);
> +bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
>  
>  unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
>  void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
> @@ -165,6 +166,11 @@ static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  	return NULL;
>  }
>  
> +static inline bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn)
> +{
> +	return false;
> +}
> +
>  static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
>  {
>  	return 0;
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 78b173c7190c..541569cb4a99 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1308,6 +1308,12 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  		 */
>  		put_page(page);
>  
> +	/* device metadata space is not recoverable */
> +	if (!pgmap_pfn_valid(pgmap, pfn)) {
> +		rc = -ENXIO;
> +		goto out;
> +	}
> +
>  	/*
>  	 * Prevent the inode from being freed while we are interrogating
>  	 * the address_space, typically this would be handled by
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 16b2fb482da1..2455bac89506 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -80,6 +80,21 @@ static unsigned long pfn_first(struct dev_pagemap *pgmap, int range_id)
>  	return pfn + vmem_altmap_offset(pgmap_altmap(pgmap));
>  }
>  
> +bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn)
> +{
> +	int i;
> +
> +	for (i = 0; i < pgmap->nr_range; i++) {
> +		struct range *range = &pgmap->ranges[i];
> +
> +		if (pfn >= PHYS_PFN(range->start) &&
> +		    pfn <= PHYS_PFN(range->end))
> +			return pfn >= pfn_first(pgmap, i);
> +	}
> +
> +	return false;
> +}
> +
>  static unsigned long pfn_end(struct dev_pagemap *pgmap, int range_id)
>  {
>  	const struct range *range = &pgmap->ranges[range_id];
> 

LGTM

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

-- 
Thanks,

David / dhildenb