[PATCH] mm: unexport __get_user_pages()

From: Lorenzo Stoakes
Date: Mon Oct 24 2016 - 05:57:36 EST


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 2 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@xxxxxxxxx>
---
include/linux/mm.h | 4 ----
mm/gup.c | 3 +--
mm/nommu.c | 2 +-
virt/kvm/kvm_main.c | 10 ++++------
4 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3a19185..a92c8d7 100644
--- a/include/linux/mm.h
+++ b/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,
diff --git a/mm/gup.c b/mm/gup.c
index 7aa113c..ec4f827 100644
--- a/mm/gup.c
+++ b/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)
{
diff --git a/mm/nommu.c b/mm/nommu.c
index db5fd17..8b8faaf 100644
--- a/mm/nommu.c
+++ b/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)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 28510e7..2907b7b 100644
--- a/virt/kvm/kvm_main.c
+++ b/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;
}

--
2.10.1