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

Ira Weiny
2019-03-25T08:26:20Z

On Fri, Mar 22, 2019 at 03:05:53PM -0700, Dan Williams wrote:
> On Sun, Mar 17, 2019 at 7:36 PM <ira.weiny@intel.com> wrote:
> >
> > From: Ira Weiny <ira.weiny@intel.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@intel.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?

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 {
>