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Date:   Thu, 31 Jan 2019 10:38:42 +0200
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Souptick Joarder <jrdr.linux@gmail.com>
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Subject: Re: [PATCHv2 1/9] mm: Introduce new vm_insert_range and
 vm_insert_range_buggy API
References: <20190131030812.GA2174@jordon-HP-15-Notebook-PC>
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On Thu, Jan 31, 2019 at 08:38:12AM +0530, Souptick Joarder wrote:
> Previouly drivers have their own way of mapping range of
> kernel pages/memory into user vma and this was done by
> invoking vm_insert_page() within a loop.
> 
> As this pattern is common across different drivers, it can
> be generalized by creating new functions and use it across
> the drivers.
> 
> vm_insert_range() is the API which could be used to mapped
> kernel memory/pages in drivers which has considered vm_pgoff
> 
> vm_insert_range_buggy() is the API which could be used to map
> range of kernel memory/pages in drivers which has not considered
> vm_pgoff. vm_pgoff is passed default as 0 for those drivers.
> 
> We _could_ then at a later "fix" these drivers which are using
> vm_insert_range_buggy() to behave according to the normal vm_pgoff
> offsetting simply by removing the _buggy suffix on the function
> name and if that causes regressions, it gives us an easy way to revert.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> Suggested-by: Russell King <linux@armlinux.org.uk>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> ---
>  include/linux/mm.h |  4 +++
>  mm/memory.c        | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/nommu.c         | 14 ++++++++++
>  3 files changed, 99 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 80bb640..25752b0 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2565,6 +2565,10 @@ unsigned long change_prot_numa(struct vm_area_struct *vma,
>  int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
>  			unsigned long pfn, unsigned long size, pgprot_t);
>  int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
> +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num);
> +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num);
>  vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  			unsigned long pfn);
>  vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
> diff --git a/mm/memory.c b/mm/memory.c
> index e11ca9d..0a4bf57 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1520,6 +1520,87 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
>  }
>  EXPORT_SYMBOL(vm_insert_page);
> 
> +/**
> + * __vm_insert_range - insert range of kernel pages into user vma
> + * @vma: user vma to map to
> + * @pages: pointer to array of source kernel pages
> + * @num: number of pages in page array
> + * @offset: user's requested vm_pgoff
> + *
> + * This allows drivers to insert range of kernel pages they've allocated
> + * into a user vma.
> + *
> + * If we fail to insert any page into the vma, the function will return
> + * immediately leaving any previously inserted pages present.  Callers
> + * from the mmap handler may immediately return the error as their caller
> + * will destroy the vma, removing any successfully inserted pages. Other
> + * callers should make their own arrangements for calling unmap_region().
> + *
> + * Context: Process context.
> + * Return: 0 on success and error code otherwise.
> + */
> +static int __vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num, unsigned long offset)
> +{
> +	unsigned long count = vma_pages(vma);
> +	unsigned long uaddr = vma->vm_start;
> +	int ret, i;
> +
> +	/* Fail if the user requested offset is beyond the end of the object */
> +	if (offset > num)
> +		return -ENXIO;
> +
> +	/* Fail if the user requested size exceeds available object size */
> +	if (count > num - offset)
> +		return -ENXIO;
> +
> +	for (i = 0; i < count; i++) {
> +		ret = vm_insert_page(vma, uaddr, pages[offset + i]);
> +		if (ret < 0)
> +			return ret;
> +		uaddr += PAGE_SIZE;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * vm_insert_range - insert range of kernel pages starts with non zero offset
> + * @vma: user vma to map to
> + * @pages: pointer to array of source kernel pages
> + * @num: number of pages in page array
> + *
> + * Maps an object consisting of `num' `pages', catering for the user's
> + * requested vm_pgoff
> + *

The elaborate description you've added to __vm_insert_range() is better put
here, as this is the "public" function.

> + * Context: Process context. Called by mmap handlers.
> + * Return: 0 on success and error code otherwise.
> + */
> +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num)
> +{
> +	return __vm_insert_range(vma, pages, num, vma->vm_pgoff);
> +}
> +EXPORT_SYMBOL(vm_insert_range);
> +
> +/**
> + * vm_insert_range_buggy - insert range of kernel pages starts with zero offset
> + * @vma: user vma to map to
> + * @pages: pointer to array of source kernel pages
> + * @num: number of pages in page array
> + *
> + * Maps a set of pages, always starting at page[0]

Here I'd add something like:

Similar to vm_insert_range(), except that it explicitly sets @vm_pgoff to
0. This function is intended for the drivers that did not consider
@vm_pgoff.

> vm_insert_range_buggy() is the API which could be used to map
> range of kernel memory/pages in drivers which has not considered
> vm_pgoff. vm_pgoff is passed default as 0 for those drivers.

> + *
> + * Context: Process context. Called by mmap handlers.
> + * Return: 0 on success and error code otherwise.
> + */
> +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num)
> +{
> +	return __vm_insert_range(vma, pages, num, 0);
> +}
> +EXPORT_SYMBOL(vm_insert_range_buggy);
> +
>  static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  			pfn_t pfn, pgprot_t prot, bool mkwrite)
>  {
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 749276b..21d101e 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -473,6 +473,20 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
>  }
>  EXPORT_SYMBOL(vm_insert_page);
> 
> +int vm_insert_range(struct vm_area_struct *vma, struct page **pages,
> +			unsigned long num)
> +{
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL(vm_insert_range);
> +
> +int vm_insert_range_buggy(struct vm_area_struct *vma, struct page **pages,
> +				unsigned long num)
> +{
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL(vm_insert_range_buggy);
> +
>  /*
>   *  sys_brk() for the most part doesn't need the global kernel
>   *  lock, except when an application is doing something nasty
> -- 
> 1.9.1
> 

-- 
Sincerely yours,
Mike.