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Date:   Fri, 22 Mar 2019 15:05:53 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     ira.weiny@...el.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Rich Felker <dalias@...c.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>, linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh <linux-sh@...r.kernel.org>, sparclinux@...r.kernel.org,
        linux-rdma@...r.kernel.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RESEND 3/7] mm/gup: Change GUP fast to use flags rather than a
 write 'bool'

On Sun, Mar 17, 2019 at 7:36 PM <ira.weiny@...el.com> wrote:
>
> From: Ira Weiny <ira.weiny@...el.com>
>
> 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@...el.com>
>
> ---
> 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? 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.

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 {

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