On 01/20/2016 06:35 PM, Dave Hansen wrote:
> Here's another revision taking Vlastimil's suggestions about
> keeping __get_user_pages_unlocked() as-is in to account.
> This does, indeed, look nicer. Now, all the "__" variants
> take a full tsk/mm and flags.
>
> He also noted that the two sites where we called gup with
> tsk=NULL were probably incorrectly changing behavior with respect
> to fault accounting. Long-term, I wonder if we should just add
> a "FOLL_" flag to make that more explicit, but for now, I've
> fixed up those sites.
>
> ---
>
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> For protection keys, we need to understand whether protections
> should be enforced in software or not. In general, we enforce
> protections when working on our own task, but not when on others.
> We call these "current" and "foreign" operations.
>
> This patch introduces a new get_user_pages() variant:
>
> get_user_pages_foreign()
>
> The plain get_user_pages() can no longer be used on mm/tasks
> other than 'current/current->mm', which is by far the most common
> way it is called. Using it makes a few of the call sites look a
> bit nicer.
>
> In other words, get_user_pages_foreign() is a replacement for
> when get_user_pages() is called on non-current tsk/mm.
>
> This also switches get_user_pages_(un)locked() over to be like
> get_user_pages() and not take a tsk/mm. There is no
> get_user_pages_foreign_(un)locked(). If someone wants that
> behavior they just have to use "__" variant and pass in
> FOLL_FOREIGN explicitly.
>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: vbabka@xxxxxxx
> Cc: jack@xxxxxxx
> ---
>
After you fix up the nommu version of __get_user_pages_unlocked() below to match
the mmu one,
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> diff -puN mm/nommu.c~get_current_user_pages mm/nommu.c
> --- a/mm/nommu.c~get_current_user_pages 2016-01-19 15:48:31.794063748 -0800
> +++ b/mm/nommu.c 2016-01-19 15:48:31.835065603 -0800
[...]
> -long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> - unsigned long start, unsigned long nr_pages,
> +long get_user_pages(unsigned long start, unsigned long nr_pages,
> + int write, int force, struct page **pages,
> + struct vm_area_struct **vmas)
> +{
> + return get_user_pages_foreign(current, current->mm, start, nr_pages,
> + write, force, pages, vmas);
> +}
> +EXPORT_SYMBOL(get_user_pages);
> +
> +long __get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> int write, int force, struct page **pages,
> unsigned int gup_flags)
> {
> long ret;
> - down_read(&mm->mmap_sem);
> - ret = get_user_pages(tsk, mm, start, nr_pages, write, force,
> - pages, NULL);
> - up_read(&mm->mmap_sem);
> + down_read(¤t->mm->mmap_sem);
> + ret = get_user_pages(start, nr_pages, write, force, pages, NULL);
> + up_read(¤t->mm->mmap_sem);
> return ret;
> }
> EXPORT_SYMBOL(__get_user_pages_unlocked);
>
> -long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> - unsigned long start, unsigned long nr_pages,
> +long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> int write, int force, struct page **pages)
> {
> - return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write,
> + return __get_user_pages_unlocked(start, nr_pages, write,
> force, pages, 0);
> }
> EXPORT_SYMBOL(get_user_pages_unlocked);
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