Re: [PATCH 09/17] mm: export access_remote_vm() symbol

[Lorenzo Stoakes <lstoakes@gmail.com>]

On Tue, Jan 03, 2023 at 08:34:57AM -0800, Fenghua Yu wrote:
> From: Dave Jiang <dave.jiang@intel.com>
>
> Export access_remote_vm() symbol for driver usage. The idxd driver would
> like to use it to write the user's completion record that the hardware
> device is not able to write to due to user page fault.
>
> Tested-by: Tony Zhu <tony.zhu@intel.com>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> ---
>  mm/memory.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index aad226daf41b..caae4deff987 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5579,6 +5579,7 @@ int access_remote_vm(struct mm_struct *mm, unsigned long addr,
>  {
>  	return __access_remote_vm(mm, addr, buf, len, gup_flags);
>  }
> +EXPORT_SYMBOL_GPL(access_remote_vm);
>
>  /*
>   * Access another process' address space.
> --
> 2.32.0
>

Can you explain what use case you have for exporting this? Currently this is
only used by procfs.

Additionally, it relies on a reference count being held on the mm which seems a
little risky exposing to a driver.

Is there a reason you can't use access_process_vm() which is exported and
additionally handles the refrencing?