[PATCH 02/10] mm: remove write/force parameters from __get_user_pages_unlocked()

Lorenzo Stoakes
2016-10-13T00:20:12Z

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 <lstoakes@gmail.com>
---
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)
+ flags |= FOLL_WRITE;
+
while (!rc && nr_pages && iov_iter_count(iter)) {
int pages = min(nr_pages, max_pages_per_loop);
size_t bytes;
@@ -104,8 +108,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
* current/current->mm
*/
pages = __get_user_pages_unlocked(task, mm, pa, pages,
- vm_write, 0, process_pages,
- FOLL_REMOTE);
+ process_pages, flags);
if (pages <= 0)
return -EFAULT;

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index db96688..8035cc1 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -84,7 +84,8 @@ static void async_pf_execute(struct work_struct *work)
* mm and might be done in another context, so we must
* use FOLL_REMOTE.
*/
- __get_user_pages_unlocked(NULL, mm, addr, 1, 1, 0, NULL, FOLL_REMOTE);
+ __get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
+ FOLL_WRITE | FOLL_REMOTE);

kvm_async_page_present_sync(vcpu, apf);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 81dfc73..28510e7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1416,10 +1416,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
down_read(&current->mm->mmap_sem);
npages = get_user_page_nowait(addr, write_fault, page);
up_read(&current->mm->mmap_sem);
- } else
+ } else {
+ unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
+
+ if (write_fault)
+ flags |= FOLL_WRITE;
+
npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
- write_fault, 0, page,
- FOLL_TOUCH|FOLL_HWPOISON);
+ page, flags);
+ }
if (npages != 1)
return npages;

--
2.10.0