Re: [RESEND 3/7] mm/gup: Change GUP fast to use flags rather than a write 'bool'

[Ira Weiny]

On Fri, Mar 22, 2019 at 03:05:53PM -0700, Dan Williams wrote:
> On Sun, Mar 17, 2019 at 7:36 PM <ira.weiny@xxxxxxxxx> wrote:
> >
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > To facilitate additional options to get_user_pages_fast() change the
> > singular write parameter to be gup_flags.
> >
> > This patch does not change any functionality.  New functionality will
> > follow in subsequent patches.
> >
> > Some of the get_user_pages_fast() call sites were unchanged because they
> > already passed FOLL_WRITE or 0 for the write parameter.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > ---
> > Changes from V1:
> >         Rebase to current merge tree
> >         arch/powerpc/mm/mmu_context_iommu.c no longer calls gup_fast
> >                 The gup_longterm was converted in patch 1
> >
> >  arch/mips/mm/gup.c                         | 11 ++++++-----
> >  arch/powerpc/kvm/book3s_64_mmu_hv.c        |  4 ++--
> >  arch/powerpc/kvm/e500_mmu.c                |  2 +-
> >  arch/s390/kvm/interrupt.c                  |  2 +-
> >  arch/s390/mm/gup.c                         | 12 ++++++------
> >  arch/sh/mm/gup.c                           | 11 ++++++-----
> >  arch/sparc/mm/gup.c                        |  9 +++++----
> >  arch/x86/kvm/paging_tmpl.h                 |  2 +-
> >  arch/x86/kvm/svm.c                         |  2 +-
> >  drivers/fpga/dfl-afu-dma-region.c          |  2 +-
> >  drivers/gpu/drm/via/via_dmablit.c          |  3 ++-
> >  drivers/infiniband/hw/hfi1/user_pages.c    |  3 ++-
> >  drivers/misc/genwqe/card_utils.c           |  2 +-
> >  drivers/misc/vmw_vmci/vmci_host.c          |  2 +-
> >  drivers/misc/vmw_vmci/vmci_queue_pair.c    |  6 ++++--
> >  drivers/platform/goldfish/goldfish_pipe.c  |  3 ++-
> >  drivers/rapidio/devices/rio_mport_cdev.c   |  4 +++-
> >  drivers/sbus/char/oradax.c                 |  2 +-
> >  drivers/scsi/st.c                          |  3 ++-
> >  drivers/staging/gasket/gasket_page_table.c |  4 ++--
> >  drivers/tee/tee_shm.c                      |  2 +-
> >  drivers/vfio/vfio_iommu_spapr_tce.c        |  3 ++-
> >  drivers/vhost/vhost.c                      |  2 +-
> >  drivers/video/fbdev/pvr2fb.c               |  2 +-
> >  drivers/virt/fsl_hypervisor.c              |  2 +-
> >  drivers/xen/gntdev.c                       |  2 +-
> >  fs/orangefs/orangefs-bufmap.c              |  2 +-
> >  include/linux/mm.h                         |  4 ++--
> >  kernel/futex.c                             |  2 +-
> >  lib/iov_iter.c                             |  7 +++++--
> >  mm/gup.c                                   | 10 +++++-----
> >  mm/util.c                                  |  8 ++++----
> >  net/ceph/pagevec.c                         |  2 +-
> >  net/rds/info.c                             |  2 +-
> >  net/rds/rdma.c                             |  3 ++-
> >  35 files changed, 79 insertions(+), 63 deletions(-)
> 
> 
> >
> > diff --git a/arch/mips/mm/gup.c b/arch/mips/mm/gup.c
> > index 0d14e0d8eacf..4c2b4483683c 100644
> > --- a/arch/mips/mm/gup.c
> > +++ b/arch/mips/mm/gup.c
> > @@ -235,7 +235,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> >   * get_user_pages_fast() - pin user pages in memory
> >   * @start:     starting user address
> >   * @nr_pages:  number of pages from start to pin
> > - * @write:     whether pages will be written to
> > + * @gup_flags: flags modifying pin behaviour
> >   * @pages:     array that receives pointers to the pages pinned.
> >   *             Should be at least nr_pages long.
> >   *
> > @@ -247,8 +247,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> >   * requested. If nr_pages is 0 or negative, returns 0. If no pages
> >   * were pinned, returns -errno.
> >   */
> > -int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> > -                       struct page **pages)
> > +int get_user_pages_fast(unsigned long start, int nr_pages,
> > +                       unsigned int gup_flags, struct page **pages)
> 
> This looks a tad scary given all related thrash especially when it's
> only 1 user that wants to do get_user_page_fast_longterm, right?

Agreed but the discussion back in Feb agreed that it would be better to make
get_user_pages_fast() use flags rather than add another *_longterm call, and I
agree.

> Maybe
> something like the following. Note I explicitly moved the flags to the
> end so that someone half paying attention that calls
> __get_user_pages_fast will get a compile error if they specify the
> args in the same order.

I did this to remain consistent with the other public calls.  They put the
"return" pages parameter at the end.  For example get_user_pages() is defined
this way with pages and vmas at the end.

long get_user_pages(unsigned long start, unsigned long nr_pages,
                unsigned int gup_flags, struct page **pages,
                struct vm_area_struct **vmas)

I'm pretty sure I got all the callers.  Is this worth making the signature
"non-standard" WRT the other calls?

Ira

> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 76ba638ceda8..c6c743bc2c68 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1505,8 +1505,15 @@ static inline long
> get_user_pages_longterm(unsigned long start,
>  }
>  #endif /* CONFIG_FS_DAX */
> 
> -int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> -                       struct page **pages);
> +
> +int __get_user_pages_fast(unsigned long start, int nr_pages,
> +               struct page **pages, unsigned int gup_flags);
> +
> +static inline int get_user_pages_fast(unsigned long start, int
> nr_pages, int write,
> +                       struct page **pages)
> +{
> +       return __get_user_pages_fast(start, nr_pages, pages, write ?
> FOLL_WRITE);
> +}
> 
>  /* Container for pinned pfns / pages */
>  struct frame_vector {
>