The patch titled
Subject: mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3
has been added to the -mm tree. Its filename is
mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3.patch
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------------------------------------------------------
From: Ira Weiny <ira.weiny@xxxxxxxxx>
Subject: mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3
Changes from V2:
Enhance commit message
Add discussion from Christoph Lameter
Fix comments
fix typo 's/uer/user'
Move FOLL_LONGTERM documentation next to FOLL_LONGTERM definition
Enhance FOLL_LONGTERM documentation
remove __always_inline from __gup_longterm_locked()
Disallow FOLL_LONGTERM in calls which are incompatible
Changes from V1:
Rebased on 5.1 merge
Adjusted for changes introduced by CONFIG_CMA
This included changing check_and_migrate_cma_pages to do the
right thing
Convert a new users of GUP longterm
io_uring.c
xdp_umem.c
Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@xxxxxxxxx
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: James Hogan <jhogan@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Mike Marshall <hubcap@xxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Rich Felker <dalias@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 29 ++++++++++++++++++++-
mm/gup.c | 59 ++++++++++++++++++++++++++-----------------
2 files changed, 64 insertions(+), 24 deletions(-)
--- a/include/linux/mm.h~mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3
+++ a/include/linux/mm.h
@@ -2557,7 +2557,34 @@ struct page *follow_page(struct vm_area_
#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
#define FOLL_COW 0x4000 /* internal GUP flag */
#define FOLL_ANON 0x8000 /* don't do file mappings */
-#define FOLL_LONGTERM 0x10000 /* mapping is intended for a long term pin */
+#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
+
+/*
+ * NOTE on FOLL_LONGTERM:
+ *
+ * FOLL_LONGTERM indicates that the page will be held for an indefinite time
+ * period _often_ under userspace control. This is contrasted with
+ * iov_iter_get_pages() where usages which are transient.
+ *
+ * FIXME: For pages which are part of a filesystem, mappings are subject to the
+ * lifetime enforced by the filesystem and we need guarantees that longterm
+ * users like RDMA and V4L2 only establish mappings which coordinate usage with
+ * the filesystem. Ideas for this coordination include revoking the longterm
+ * pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was
+ * added after the problem with filesystems was found FS DAX VMAs are
+ * specifically failed. Filesystem pages are still subject to bugs and use of
+ * FOLL_LONGTERM should be avoided on those pages.
+ *
+ * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call.
+ * Currently only get_user_pages() and get_user_pages_fast() support this flag
+ * and calls to get_user_pages_[un]locked are specifically not allowed. This
+ * is due to an incompatibility with the FS DAX check and
+ * FAULT_FLAG_ALLOW_RETRY
+ *
+ * In the CMA case: longterm pins in a CMA region would unnecessarily fragment
+ * that region. And so CMA attempts to migrate the page before pinning when
+ * FOLL_LONGTERM is specified.
+ */
static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
{
--- a/mm/gup.c~mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3
+++ a/mm/gup.c
@@ -1008,6 +1008,15 @@ long get_user_pages_locked(unsigned long
unsigned int gup_flags, struct page **pages,
int *locked)
{
+ /*
+ * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+ * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+ * vmas. As there are no users of this flag in this call we simply
+ * disallow this option for now.
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+ return -EINVAL;
+
return __get_user_pages_locked(current, current->mm, start, nr_pages,
pages, NULL, locked,
gup_flags | FOLL_TOUCH);
@@ -1036,6 +1045,15 @@ long get_user_pages_unlocked(unsigned lo
int locked = 1;
long ret;
+ /*
+ * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+ * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+ * vmas. As there are no users of this flag in this call we simply
+ * disallow this option for now.
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+ return -EINVAL;
+
down_read(&mm->mmap_sem);
ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
&locked, gup_flags | FOLL_TOUCH);
@@ -1106,6 +1124,15 @@ long get_user_pages_remote(struct task_s
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *locked)
{
+ /*
+ * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+ * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+ * vmas. As there are no users of this flag in this call we simply
+ * disallow this option for now.
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+ return -EINVAL;
+
return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
locked,
gup_flags | FOLL_TOUCH | FOLL_REMOTE);
@@ -1276,30 +1303,16 @@ static long check_and_migrate_cma_pages(
#endif
/*
- * __gup_longterm_locked() is a wrapper for __get_uer_pages_locked which
- * allows us to process the FOLL_LONGTERM flag if present.
- *
- * FOLL_LONGTERM Checks for either DAX VMAs or PPC CMA regions and either fails
- * the pin or attempts to migrate the page as appropriate.
- *
- * In the filesystem-dax case mappings are subject to the lifetime enforced by
- * the filesystem and we need guarantees that longterm users like RDMA and V4L2
- * only establish mappings that have a kernel enforced revocation mechanism.
- *
- * In the CMA case pages can't be pinned in a CMA region as this would
- * unnecessarily fragment that region. So CMA attempts to migrate the page
- * before pinning.
- *
- * "longterm" == userspace controlled elevated page count lifetime.
- * Contrast this to iov_iter_get_pages() usages which are transient.
+ * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
+ * allows us to process the FOLL_LONGTERM flag.
*/
-static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
- struct mm_struct *mm,
- unsigned long start,
- unsigned long nr_pages,
- struct page **pages,
- struct vm_area_struct **vmas,
- unsigned int gup_flags)
+static long __gup_longterm_locked(struct task_struct *tsk,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long nr_pages,
+ struct page **pages,
+ struct vm_area_struct **vmas,
+ unsigned int gup_flags)
{
struct vm_area_struct **vmas_tmp = vmas;
unsigned long flags = 0;
_
Patches currently in -mm which might be from ira.weiny@xxxxxxxxx are
mm-gup-replace-get_user_pages_longterm-with-foll_longterm.patch
mm-gup-replace-get_user_pages_longterm-with-foll_longterm-v3.patch
mm-gup-change-write-parameter-to-flags-in-fast-walk.patch
mm-gup-change-gup-fast-to-use-flags-rather-than-a-write-bool.patch
mm-gup-add-foll_longterm-capability-to-gup-fast.patch
mm-gup-add-foll_longterm-capability-to-gup-fast-v3.patch
ib-hfi1-use-the-new-foll_longterm-flag-to-get_user_pages_fast.patch
ib-hfi1-use-the-new-foll_longterm-flag-to-get_user_pages_fast-v3.patch
ib-qib-use-the-new-foll_longterm-flag-to-get_user_pages_fast.patch
ib-mthca-use-the-new-foll_longterm-flag-to-get_user_pages_fast.patch
