On 13/10/2016 02:20, Lorenzo Stoakes wrote:
> This patch removes the write and force parameters from
> __get_user_pages_unlocked() to make the use of FOLL_FORCE explicit in callers
> as
> use of this flag can result in surprising behaviour (and hence bugs) within
> the
> mm subsystem.
>
> Signed-off-by: Lorenzo Stoakes
> ---
> include/linux/mm.h | 3 +--
> mm/gup.c | 17 +
> mm/nommu.c | 12 +---
> mm/process_vm_access.c | 7 +--
> virt/kvm/async_pf.c| 3 ++-
> virt/kvm/kvm_main.c| 11 ---
> 6 files changed, 34 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e9caec6..2db98b6 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1285,8 +1285,7 @@ long get_user_pages_locked(unsigned long start,
> unsigned long nr_pages,
> int write, int force, struct page **pages, int *locked);
> long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> unsigned long start, unsigned long nr_pages,
> -int write, int force, struct page **pages,
> -unsigned int gup_flags);
> +struct page **pages, unsigned int gup_flags);
> long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> int write, int force, struct page **pages);
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> diff --git a/mm/gup.c b/mm/gup.c
> index ba83942..3d620dd 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -865,17 +865,11 @@ EXPORT_SYMBOL(get_user_pages_locked);
> */
> __always_inline long __get_user_pages_unlocked(struct task_struct *tsk,
> struct mm_struct *mm,
> unsigned long start, unsigned
> long nr_pages,
> -int write, int force, struct
> page **pages,
> -unsigned int gup_flags)
> +struct page **pages, unsigned
> int gup_flags)
> {
> long ret;
> int locked = 1;
>
> - if (write)
> - gup_flags |= FOLL_WRITE;
> - if (force)
> - gup_flags |= FOLL_FORCE;
> -
> down_read(&mm->mmap_sem);
> ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
> &locked, false, gup_flags);
> @@ -905,8 +899,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
> long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>int write, int force, struct page **pages)
> {
> + unsigned int flags = FOLL_TOUCH;
> +
> + if (write)
> + flags |= FOLL_WRITE;
> + if (force)
> + flags |= FOLL_FORCE;
> +
> return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
> - write, force, pages, FOLL_TOUCH);
> + pages, flags);
> }
> EXPORT_SYMBOL(get_user_pages_unlocked);
>
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 95daf81..925dcc1 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -185,8 +185,7 @@ EXPORT_SYMBOL(get_user_pages_locked);
>
> long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
> unsigned long start, unsigned long nr_pages,
> -int write, int force, struct page **pages,
> -unsigned int gup_flags)
> +struct page **pages, unsigned int gup_flags)
> {
> long ret;
> down_read(&mm->mmap_sem);
> @@ -200,8 +199,15 @@ EXPORT_SYMBOL(__get_user_pages_unlocked);
> long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>int write, int force, struct page **pages)
> {
> + unsigned int flags = 0;
> +
> + if (write)
> + flags |= FOLL_WRITE;
> + if (force)
> + flags |= FOLL_FORCE;
> +
> return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
> - write, force, pages, 0);
> + pages, flags);
> }
> EXPORT_SYMBOL(get_user_pages_unlocked);
>
> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
> index 07514d4..be8dc8d 100644
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -88,12 +88,16 @@ static int process_vm_rw_single_vec(unsigned long addr,
> ssize_t rc = 0;
> unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
> / sizeof(struct pages *);
> + unsigned int flags = FOLL_REMOTE;
>
> /* Work out address and page range required */
> if (len == 0)
> return 0;
> nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
>
> + if (vm_write)
> + flag