On 13/10/2016 02:20, Lorenzo Stoakes wrote:
> 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;
>  
> 

Acked-by: Paolo Bonzini <pbonz...@redhat.com>
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