Re: [Xen-devel] [PATCH v3 1/9] mm: Introduce new vm_insert_range API

[Robin Murphy <robin.murphy@xxxxxxx>]

On 06/12/2018 18:39, 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 a new function and use it across
> the drivers.
>
> vm_insert_range is the new API which will be used to map a
> range of kernel memory/pages to user vma.
>
> This API is tested by Heiko for Rockchip drm driver, on rk3188,
> rk3288, rk3328 and rk3399 with graphics.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
> ---
>   include/linux/mm.h |  2 ++
>   mm/memory.c        | 38 ++++++++++++++++++++++++++++++++++++++
>   mm/nommu.c         |  7 +++++++
>   3 files changed, 47 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index fcf9cc9..2bc399f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2506,6 +2506,8 @@ 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, unsigned long addr,
> +                       struct page **pages, unsigned long page_count);
>   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 15c417e..84ea46c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1478,6 +1478,44 @@ static int insert_page(struct vm_area_struct *vma, 
> unsigned long addr,
>   }
>   
>   /**
> + * vm_insert_range - insert range of kernel pages into user vma
> + * @vma: user vma to map to
> + * @addr: target user address of this page
> + * @pages: pointer to array of source kernel pages
> + * @page_count: number of pages need to insert into user vma
> + *
> + * This allows drivers to insert range of kernel pages they've allocated
> + * into a user vma. This is a generic function which drivers can use
> + * rather than using their own way of mapping range of kernel pages into
> + * 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. Called by mmap handlers.
> + * Return: 0 on success and error code otherwise
> + */
> +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr,
> +                       struct page **pages, unsigned long page_count)
> +{
> +       unsigned long uaddr = addr;
> +       int ret = 0, i;
Some of the sites being replaced were effectively ensuring that vma and 
pages were mutually compatible as an initial condition - would it be 
worth adding something here for robustness, e.g.:
+       if (page_count != vma_pages(vma))
+               return -ENXIO;

?

(then you could also clean up a couple more places where you're not 
already removing such checks)
Robin.

> +
> +       for (i = 0; i < page_count; i++) {
> +               ret = vm_insert_page(vma, uaddr, pages[i]);
> +               if (ret < 0)
> +                       return ret;
> +               uaddr += PAGE_SIZE;
> +       }
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL(vm_insert_range);
> +
> +/**
>    * vm_insert_page - insert single page into user vma
>    * @vma: user vma to map to
>    * @addr: target user address of this page
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 749276b..d6ef5c7 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -473,6 +473,13 @@ 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, unsigned long addr,
> +                       struct page **pages, unsigned long page_count)
> +{
> +       return -EINVAL;
> +}
> +EXPORT_SYMBOL(vm_insert_range);
> +
>   /*
>    *  sys_brk() for the most part doesn't need the global kernel
>    *  lock, except when an application is doing something nasty
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