Re: [PATCH 1/2] mm: add locked parameter to get_user_pages_remote()

[Michal Hocko]

On Thu 27-10-16 10:51:40, Lorenzo Stoakes wrote:
> This patch adds a int *locked parameter to get_user_pages_remote() to allow
> VM_FAULT_RETRY faulting behaviour similar to get_user_pages_[un]locked().
> 
> Taking into account the previous adjustments to get_user_pages*() functions
> allowing for the passing of gup_flags, we are now in a position where
> __get_user_pages_unlocked() need only be exported for his ability to allow
> VM_FAULT_RETRY behaviour, this adjustment allows us to subsequently unexport
> __get_user_pages_unlocked() as well as allowing for future flexibility in the
> use of get_user_pages_remote().

I would also add that this shouldn't introduce any functional change.

> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  drivers/gpu/drm/etnaviv/etnaviv_gem.c   |  2 +-
>  drivers/gpu/drm/i915/i915_gem_userptr.c |  2 +-
>  drivers/infiniband/core/umem_odp.c      |  2 +-
>  fs/exec.c                               |  2 +-
>  include/linux/mm.h                      |  2 +-
>  kernel/events/uprobes.c                 |  4 ++--
>  mm/gup.c                                | 12 ++++++++----
>  mm/memory.c                             |  2 +-
>  security/tomoyo/domain.c                |  2 +-
>  9 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> index 0370b84..0c69a97f 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> @@ -763,7 +763,7 @@ static struct page **etnaviv_gem_userptr_do_get_pages(
>  	down_read(&mm->mmap_sem);
>  	while (pinned < npages) {
>  		ret = get_user_pages_remote(task, mm, ptr, npages - pinned,
> -					    flags, pvec + pinned, NULL);
> +					    flags, pvec + pinned, NULL, NULL);
>  		if (ret < 0)
>  			break;
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index c6f780f..836b525 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -522,7 +522,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
>  					 obj->userptr.ptr + pinned * PAGE_SIZE,
>  					 npages - pinned,
>  					 flags,
> -					 pvec + pinned, NULL);
> +					 pvec + pinned, NULL, NULL);
>  				if (ret < 0)
>  					break;
> 
> diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
> index 1f0fe32..6b079a3 100644
> --- a/drivers/infiniband/core/umem_odp.c
> +++ b/drivers/infiniband/core/umem_odp.c
> @@ -578,7 +578,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
>  		 */
>  		npages = get_user_pages_remote(owning_process, owning_mm,
>  				user_virt, gup_num_pages,
> -				flags, local_page_list, NULL);
> +				flags, local_page_list, NULL, NULL);
>  		up_read(&owning_mm->mmap_sem);
> 
>  		if (npages < 0)
> diff --git a/fs/exec.c b/fs/exec.c
> index 4e497b9..2cf049d 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -209,7 +209,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
>  	 * doing the exec and bprm->mm is the new process's mm.
>  	 */
>  	ret = get_user_pages_remote(current, bprm->mm, pos, 1, gup_flags,
> -			&page, NULL);
> +			&page, NULL, NULL);
>  	if (ret <= 0)
>  		return NULL;
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a92c8d7..cc15445 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1274,7 +1274,7 @@ extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
>  long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  			    unsigned long start, unsigned long nr_pages,
>  			    unsigned int gup_flags, struct page **pages,
> -			    struct vm_area_struct **vmas);
> +			    struct vm_area_struct **vmas, int *locked);
>  long get_user_pages(unsigned long start, unsigned long nr_pages,
>  			    unsigned int gup_flags, struct page **pages,
>  			    struct vm_area_struct **vmas);
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index f9ec9ad..215871b 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -301,7 +301,7 @@ int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
>  retry:
>  	/* Read the page with vaddr into memory */
>  	ret = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &old_page,
> -			&vma);
> +			&vma, NULL);
>  	if (ret <= 0)
>  		return ret;
> 
> @@ -1712,7 +1712,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
>  	 * essentially a kernel access to the memory.
>  	 */
>  	result = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &page,
> -			NULL);
> +			NULL, NULL);
>  	if (result < 0)
>  		return result;
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ec4f827..0567851 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -920,6 +920,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
>   *		only intends to ensure the pages are faulted in.
>   * @vmas:	array of pointers to vmas corresponding to each page.
>   *		Or NULL if the caller does not require them.
> + * @locked:	pointer to lock flag indicating whether lock is held and
> + *		subsequently whether VM_FAULT_RETRY functionality can be
> + *		utilised. Lock must initially be held.
>   *
>   * Returns number of pages pinned. This may be fewer than the number
>   * requested. If nr_pages is 0 or negative, returns 0. If no pages
> @@ -963,10 +966,10 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
>  long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  		unsigned long start, unsigned long nr_pages,
>  		unsigned int gup_flags, struct page **pages,
> -		struct vm_area_struct **vmas)
> +		struct vm_area_struct **vmas, int *locked)
>  {
>  	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
> -				       NULL, false,
> +				       locked, true,
>  				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
>  }
>  EXPORT_SYMBOL(get_user_pages_remote);
> @@ -974,8 +977,9 @@ EXPORT_SYMBOL(get_user_pages_remote);
>  /*
>   * This is the same as get_user_pages_remote(), just with a
>   * less-flexible calling convention where we assume that the task
> - * and mm being operated on are the current task's.  We also
> - * obviously don't pass FOLL_REMOTE in here.
> + * and mm being operated on are the current task's and don't allow
> + * passing of a locked parameter.  We also obviously don't pass
> + * FOLL_REMOTE in here.
>   */
>  long get_user_pages(unsigned long start, unsigned long nr_pages,
>  		unsigned int gup_flags, struct page **pages,
> diff --git a/mm/memory.c b/mm/memory.c
> index e18c57b..2f3949b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3883,7 +3883,7 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
>  		struct page *page = NULL;
> 
>  		ret = get_user_pages_remote(tsk, mm, addr, 1,
> -				gup_flags, &page, &vma);
> +				gup_flags, &page, &vma, NULL);
>  		if (ret <= 0) {
>  #ifndef CONFIG_HAVE_IOREMAP_PROT
>  			break;
> diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
> index 682b73a..838ffa7 100644
> --- a/security/tomoyo/domain.c
> +++ b/security/tomoyo/domain.c
> @@ -881,7 +881,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
>  	 * the execve().
>  	 */
>  	if (get_user_pages_remote(current, bprm->mm, pos, 1,
> -				FOLL_FORCE, &page, NULL) <= 0)
> +				FOLL_FORCE, &page, NULL, NULL) <= 0)
>  		return false;
>  #else
>  	page = bprm->page[pos / PAGE_SIZE];
> --
> 2.10.1

-- 
Michal Hocko
SUSE Labs