mm: unexport __get_user_pages()

This patch unexports the low-level __get_user_pages() function.

Recent refactoring of the get_user_pages* functions allow flags to be
passed through get_user_pages() which eliminates the need for access to
this function from its one user, kvm.

We can see that the two calls to get_user_pages() which replace
__get_user_pages() in kvm_main.c are equivalent by examining their call
stacks:

  get_user_page_nowait():
    get_user_pages(start, 1, flags, page, NULL)
    __get_user_pages_locked(current, current->mm, start, 1, page, NULL, NULL,
			    false, flags | FOLL_TOUCH)
    __get_user_pages(current, current->mm, start, 1,
		     flags | FOLL_TOUCH | FOLL_GET, page, NULL, NULL)

  check_user_page_hwpoison():
    get_user_pages(addr, 1, flags, NULL, NULL)
    __get_user_pages_locked(current, current->mm, addr, 1, NULL, NULL, NULL,
			    false, flags | FOLL_TOUCH)
    __get_user_pages(current, current->mm, addr, 1, flags | FOLL_TOUCH, NULL,
		     NULL, NULL)
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -1271,10 +1271,6 @@ extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *
 extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
 		void *buf, int len, unsigned int gup_flags);
 
-long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
-		      unsigned long start, unsigned long nr_pages,
-		      unsigned int foll_flags, struct page **pages,
-		      struct vm_area_struct **vmas, int *nonblocking);
 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,

mm/gup.c

@@ -526,7 +526,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  * instead of __get_user_pages. __get_user_pages should be used only if
  * you need some special @gup_flags.
  */
-long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+static long __get_user_pages(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, int *nonblocking)
@@ -631,7 +631,6 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 	} while (nr_pages);
 	return i;
 }
-EXPORT_SYMBOL(__get_user_pages);
 
 bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
 {

mm/nommu.c

@@ -109,7 +109,7 @@ unsigned int kobjsize(const void *objp)
 	return PAGE_SIZE << compound_order(page);
 }
 
-long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
+static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		      unsigned long start, unsigned long nr_pages,
 		      unsigned int foll_flags, struct page **pages,
 		      struct vm_area_struct **vmas, int *nonblocking)

virt/kvm/kvm_main.c

@@ -1346,21 +1346,19 @@ unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *w
 static int get_user_page_nowait(unsigned long start, int write,
 		struct page **page)
 {
-	int flags = FOLL_TOUCH | FOLL_NOWAIT | FOLL_HWPOISON | FOLL_GET;
+	int flags = FOLL_NOWAIT | FOLL_HWPOISON;
 
 	if (write)
 		flags |= FOLL_WRITE;
 
-	return __get_user_pages(current, current->mm, start, 1, flags, page,
-			NULL, NULL);
+	return get_user_pages(start, 1, flags, page, NULL);
 }
 
 static inline int check_user_page_hwpoison(unsigned long addr)
 {
-	int rc, flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_WRITE;
+	int rc, flags = FOLL_HWPOISON | FOLL_WRITE;
 
-	rc = __get_user_pages(current, current->mm, addr, 1,
-			      flags, NULL, NULL, NULL);
+	rc = get_user_pages(addr, 1, flags, NULL, NULL);
 	return rc == -EHWPOISON;
 }