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SubjectRe: [PATCH 2/3] mm/gup: Introduce get_user_pages_fast_longterm()
On Mon, Feb 11, 2019 at 12:16:42PM -0800, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Users of get_user_pages_fast are not protected against mapping
> pages within FS DAX. Introduce a call which protects them.
>
> We do this by checking for DEVMAP pages during the fast walk and
> falling back to the longterm gup call to check for FS DAX if needed.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> include/linux/mm.h | 8 ++++
> mm/gup.c | 102 +++++++++++++++++++++++++++++++++++----------
> 2 files changed, 88 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 80bb6408fe73..8f831c823630 100644
> +++ b/include/linux/mm.h
> @@ -1540,6 +1540,8 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
> unsigned int gup_flags, struct page **pages,
> struct vm_area_struct **vmas);
> +int get_user_pages_fast_longterm(unsigned long start, int nr_pages, bool write,
> + struct page **pages);
> #else
> static inline long get_user_pages_longterm(unsigned long start,
> unsigned long nr_pages, unsigned int gup_flags,
> @@ -1547,6 +1549,11 @@ static inline long get_user_pages_longterm(unsigned long start,
> {
> return get_user_pages(start, nr_pages, gup_flags, pages, vmas);
> }
> +static inline int get_user_pages_fast_longterm(unsigned long start, int nr_pages,
> + bool write, struct page **pages)
> +{
> + return get_user_pages_fast(start, nr_pages, write, pages);
> +}
> #endif /* CONFIG_FS_DAX */
>
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> @@ -2615,6 +2622,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
> #define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
> #define FOLL_COW 0x4000 /* internal GUP flag */
> #define FOLL_ANON 0x8000 /* don't do file mappings */
> +#define FOLL_LONGTERM 0x10000 /* mapping is intended for a long term pin */

If we are adding a new flag, maybe we should get rid of the 'longterm'
entry points and just rely on the callers to pass the flag?

Jason

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