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 <lstoa...@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

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