[PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM

[PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM

[John Hubbard]

OK, here we go. Any VFIO and Infiniband runtime testing from anyone, is
especially welcome here.

Changes since v3:

* VFIO fix (patch 8): applied further cleanup: removed a pre-existing,
  unnecessary release and reacquire of mmap_sem. Moved the DAX vma
  checks from the vfio call site, to gup internals, and added comments
  (and commit log) to clarify.

* Due to the above, made a corresponding fix to the
  pin_longterm_pages_remote(), which was actually calling the wrong
  gup internal function.

* Changed put_user_page() comments, to refer to pin*() APIs, rather than
  get_user_pages*() APIs.

* Reverted an accidental whitespace-only change in the IB ODP code.

* Added a few more reviewed-by tags.


Changes since v2:

* Added a patch to convert IB/umem from normal gup, to gup_fast(). This
  is also posted separately, in order to hopefully get some runtime
  testing.

* Changed the page devmap code to be a little clearer,
  thanks to Jerome for that.

* Split out the page devmap changes into a separate patch (and moved
  Ira's Signed-off-by to that patch).

* Fixed my bug in IB: ODP code does not require pin_user_pages()
  semantics. Therefore, revert the put_user_page() calls to put_page(),
  and leave the get_user_pages() call as-is.

      * As part of the revert, I am proposing here a change directly
        from put_user_pages(), to release_pages(). I'd feel better if
        someone agrees that this is the best way. It uses the more
        efficient release_pages(), instead of put_page() in a loop,
        and keep the change to just a few character on one line,
        but OTOH it is not a pure revert.

* Loosened the FOLL_LONGTERM restrictions in the
  __get_user_pages_locked() implementation, and used that in order
  to fix up a VFIO bug. Thanks to Jason for that idea.

    * Note the use of release_pages() in IB: is that OK?

* Added a few more WARN's and clarifying comments nearby.

* Many documentation improvements in various comments.

* Moved the new pin_user_pages.rst from Documentation/vm/ to
  Documentation/core-api/ .

* Commit descriptions: added clarifying notes to the three patches
  (drm/via, fs/io_uring, net/xdp) that already had put_user_page()
  calls in place.

* Collected all pending Reviewed-by and Acked-by tags, from v1 and v2
  email threads.

* Lot of churn from v2 --> v3, so it's possible that new bugs
  sneaked in.

NOT DONE: separate patchset is required:

* __get_user_pages_locked(): stop compensating for
  buggy callers who failed to set FOLL_GET. Instead, assert
  that FOLL_GET is set (and fail if it's not).

======================================================================
Original cover letter (edited to fix up the patch description numbers)

This applies cleanly to linux-next and mmotm, and also to linux.git if
linux-next's commit 20cac10710c9 ("mm/gup_benchmark: fix MAP_HUGETLB
case") is first applied there.

This provides tracking of dma-pinned pages. This is a prerequisite to
solving the larger problem of proper interactions between file-backed
pages, and [R]DMA activities, as discussed in [1], [2], [3], and in
a remarkable number of email threads since about 2017. :)

A new internal gup flag, FOLL_PIN is introduced, and thoroughly
documented in the last patch's Documentation/vm/pin_user_pages.rst.

I believe that this will provide a good starting point for doing the
layout lease work that Ira Weiny has been working on. That's because
these new wrapper functions provide a clean, constrained, systematically
named set of functionality that, again, is required in order to even
know if a page is "dma-pinned".

In contrast to earlier approaches, the page tracking can be
incrementally applied to the kernel call sites that, until now, have
been simply calling get_user_pages() ("gup"). In other words, opt-in by
changing from this:

    get_user_pages() (sets FOLL_GET)
    put_page()

to this:
    pin_user_pages() (sets FOLL_PIN)
    put_user_page()

Because there are interdependencies with FOLL_LONGTERM, a similar
conversion as for FOLL_PIN, was applied. The change was from this:

    get_user_pages(FOLL_LONGTERM) (also sets FOLL_GET)
    put_page()

to this:
    pin_longterm_pages() (sets FOLL_PIN | FOLL_LONGTERM)
    put_user_page()

============================================================
Patch summary:

* Patches 1-8: refactoring and preparatory cleanup, independent fixes

* Patch 9: introduce pin_user_pages(), FOLL_PIN, but no functional
           changes yet
* Patches 10-15: Convert existing put_user_page() callers, to use the
                new pin*()
* Patch 16: Activate tracking of FOLL_PIN pages.
* Patches 17-19: convert FOLL_LONGTERM callers
* Patches: 20-22: gup_benchmark and run_vmtests support
* Patch 23: enforce FOLL_LONGTERM as a gup-internal (only) flag

============================================================
Testing:

* I've done some overall kernel testing (LTP, and a few other goodies),
  and some directed testing to exercise some of the changes. And as you
  can see, gup_benchmark is enhanced to exercise this. Basically, I've been
  able to runtime test the core get_user_pages() and pin_user_pages() and
  related routines, but not so much on several of the call sites--but those
  are generally just a couple of lines changed, each.

  Not much of the kernel is actually using this, which on one hand
  reduces risk quite a lot. But on the other hand, testing coverage
  is low. So I'd love it if, in particular, the Infiniband and PowerPC
  folks could do a smoke test of this series for me.

  Also, my runtime testing for the call sites so far is very weak:

    * io_uring: Some directed tests from liburing exercise this, and they pass.
    * process_vm_access.c: A small directed test passes.
    * gup_benchmark: the enhanced version hits the new gup.c code, and passes.
    * infiniband (still only have crude "IB pingpong" working, on a
                  good day: it's not exercising my conversions at runtime...)
    * VFIO: compiles (I'm vowing to set up a run time test soon, but it's
                      not ready just yet)
    * powerpc: it compiles...
    * drm/via: compiles...
    * goldfish: compiles...
    * net/xdp: compiles...
    * media/v4l2: compiles...

============================================================
Next:

* Get the block/bio_vec sites converted to use pin_user_pages().

* Work with Ira and Dave Chinner to weave this together with the
  layout lease stuff.

============================================================

[1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/
[2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/
[3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/

John Hubbard (23):
  mm/gup: pass flags arg to __gup_device_* functions
  mm/gup: factor out duplicate code from four routines
  mm/gup: move try_get_compound_head() to top, fix minor issues
  mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
  goldish_pipe: rename local pin_user_pages() routine
  IB/umem: use get_user_pages_fast() to pin DMA pages
  media/v4l2-core: set pages dirty upon releasing DMA buffers
  vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM
  mm/gup: introduce pin_user_pages*() and FOLL_PIN
  goldish_pipe: convert to pin_user_pages() and put_user_page()
  IB/{core,hw,umem}: set FOLL_PIN, FOLL_LONGTERM via
    pin_longterm_pages*()
  mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()
  drm/via: set FOLL_PIN via pin_user_pages_fast()
  fs/io_uring: set FOLL_PIN via pin_user_pages()
  net/xdp: set FOLL_PIN via pin_user_pages()
  mm/gup: track FOLL_PIN pages
  media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page()
    conversion
  vfio, mm: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion
  powerpc: book3s64: convert to pin_longterm_pages() and put_user_page()
  mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding
    "1"
  mm/gup_benchmark: support pin_user_pages() and related calls
  selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN
    coverage
  mm/gup: remove support for gup(FOLL_LONGTERM)

 Documentation/core-api/index.rst            |   1 +
 Documentation/core-api/pin_user_pages.rst   | 218 +++++++
 arch/powerpc/mm/book3s64/iommu_api.c        |  15 +-
 drivers/gpu/drm/via/via_dmablit.c           |   2 +-
 drivers/infiniband/core/umem.c              |  17 +-
 drivers/infiniband/core/umem_odp.c          |  13 +-
 drivers/infiniband/hw/hfi1/user_pages.c     |   4 +-
 drivers/infiniband/hw/mthca/mthca_memfree.c |   3 +-
 drivers/infiniband/hw/qib/qib_user_pages.c  |   8 +-
 drivers/infiniband/hw/qib/qib_user_sdma.c   |   2 +-
 drivers/infiniband/hw/usnic/usnic_uiom.c    |   9 +-
 drivers/infiniband/sw/siw/siw_mem.c         |   5 +-
 drivers/media/v4l2-core/videobuf-dma-sg.c   |  10 +-
 drivers/platform/goldfish/goldfish_pipe.c   |  35 +-
 drivers/vfio/vfio_iommu_type1.c             |  30 +-
 fs/io_uring.c                               |   5 +-
 include/linux/mm.h                          | 164 ++++-
 include/linux/mmzone.h                      |   2 +
 include/linux/page_ref.h                    |  10 +
 mm/gup.c                                    | 636 ++++++++++++++++----
 mm/gup_benchmark.c                          |  87 ++-
 mm/huge_memory.c                            |  54 +-
 mm/hugetlb.c                                |  39 +-
 mm/memremap.c                               |  67 +--
 mm/process_vm_access.c                      |  28 +-
 mm/vmstat.c                                 |   2 +
 net/xdp/xdp_umem.c                          |   4 +-
 tools/testing/selftests/vm/gup_benchmark.c  |  34 +-
 tools/testing/selftests/vm/run_vmtests      |  22 +
 29 files changed, 1191 insertions(+), 335 deletions(-)
 create mode 100644 Documentation/core-api/pin_user_pages.rst

-- 
2.24.0

[PATCH v4 01/23] mm/gup: pass flags arg to __gup_device_* functions

[John Hubbard]

A subsequent patch requires access to gup flags, so
pass the flags argument through to the __gup_device_*
functions.

Also placate checkpatch.pl by shortening a nearby line.

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 8f236a335ae9..85caf76b3012 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1890,7 +1890,8 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 
 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
 static int __gup_device_huge(unsigned long pfn, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+			     unsigned long end, unsigned int flags,
+			     struct page **pages, int *nr)
 {
 	int nr_start = *nr;
 	struct dev_pagemap *pgmap = NULL;
@@ -1916,13 +1917,14 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 }
 
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	unsigned long fault_pfn;
 	int nr_start = *nr;
 
 	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
-	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
 		return 0;
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
@@ -1933,13 +1935,14 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 }
 
 static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	unsigned long fault_pfn;
 	int nr_start = *nr;
 
 	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
-	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
 		return 0;
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
@@ -1950,14 +1953,16 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 }
 #else
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	BUILD_BUG();
 	return 0;
 }
 
 static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	BUILD_BUG();
 	return 0;
@@ -2062,7 +2067,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (pmd_devmap(orig)) {
 		if (unlikely(flags & FOLL_LONGTERM))
 			return 0;
-		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
+		return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
+					     pages, nr);
 	}
 
 	refs = 0;
@@ -2092,7 +2098,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 }
 
 static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages, int *nr)
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
 {
 	struct page *head, *page;
 	int refs;
@@ -2103,7 +2110,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 	if (pud_devmap(orig)) {
 		if (unlikely(flags & FOLL_LONGTERM))
 			return 0;
-		return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
+		return __gup_device_huge_pud(orig, pudp, addr, end, flags,
+					     pages, nr);
 	}
 
 	refs = 0;
-- 
2.24.0

[PATCH v4 02/23] mm/gup: factor out duplicate code from four routines

[John Hubbard]

There are four locations in gup.c that have a fair amount of code
duplication. This means that changing one requires making the same
changes in four places, not to mention reading the same code four
times, and wondering if there are subtle differences.

Factor out the common code into static functions, thus reducing the
overall line count and the code's complexity.

Also, take the opportunity to slightly improve the efficiency of the
error cases, by doing a mass subtraction of the refcount, surrounded
by get_page()/put_page().

Also, further simplify (slightly), by waiting until the the successful
end of each routine, to increment *nr.

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 104 ++++++++++++++++++++++++-------------------------------
 1 file changed, 45 insertions(+), 59 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 85caf76b3012..199da99e8ffc 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1969,6 +1969,34 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
 }
 #endif
 
+static int __record_subpages(struct page *page, unsigned long addr,
+			     unsigned long end, struct page **pages, int nr)
+{
+	int nr_recorded_pages = 0;
+
+	do {
+		pages[nr] = page;
+		nr++;
+		page++;
+		nr_recorded_pages++;
+	} while (addr += PAGE_SIZE, addr != end);
+	return nr_recorded_pages;
+}
+
+static void put_compound_head(struct page *page, int refs)
+{
+	/* Do a get_page() first, in case refs == page->_refcount */
+	get_page(page);
+	page_ref_sub(page, refs);
+	put_page(page);
+}
+
+static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
+{
+	*nr += nr_recorded_pages;
+	SetPageReferenced(head);
+}
+
 #ifdef CONFIG_ARCH_HAS_HUGEPD
 static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
 				      unsigned long sz)
@@ -1998,33 +2026,20 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 	/* hugepages are never "special" */
 	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 
-	refs = 0;
 	head = pte_page(pte);
-
 	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
-	do {
-		VM_BUG_ON(compound_head(page) != head);
-		pages[*nr] = page;
-		(*nr)++;
-		page++;
-		refs++;
-	} while (addr += PAGE_SIZE, addr != end);
+	refs = __record_subpages(page, addr, end, pages, *nr);
 
 	head = try_get_compound_head(head, refs);
-	if (!head) {
-		*nr -= refs;
+	if (!head)
 		return 0;
-	}
 
 	if (unlikely(pte_val(pte) != pte_val(*ptep))) {
-		/* Could be optimized better */
-		*nr -= refs;
-		while (refs--)
-			put_page(head);
+		put_compound_head(head, refs);
 		return 0;
 	}
 
-	SetPageReferenced(head);
+	__huge_pt_done(head, refs, nr);
 	return 1;
 }
 
@@ -2071,29 +2086,19 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 					     pages, nr);
 	}
 
-	refs = 0;
 	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
-	do {
-		pages[*nr] = page;
-		(*nr)++;
-		page++;
-		refs++;
-	} while (addr += PAGE_SIZE, addr != end);
+	refs = __record_subpages(page, addr, end, pages, *nr);
 
 	head = try_get_compound_head(pmd_page(orig), refs);
-	if (!head) {
-		*nr -= refs;
+	if (!head)
 		return 0;
-	}
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
-		*nr -= refs;
-		while (refs--)
-			put_page(head);
+		put_compound_head(head, refs);
 		return 0;
 	}
 
-	SetPageReferenced(head);
+	__huge_pt_done(head, refs, nr);
 	return 1;
 }
 
@@ -2114,29 +2119,19 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 					     pages, nr);
 	}
 
-	refs = 0;
 	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
-	do {
-		pages[*nr] = page;
-		(*nr)++;
-		page++;
-		refs++;
-	} while (addr += PAGE_SIZE, addr != end);
+	refs = __record_subpages(page, addr, end, pages, *nr);
 
 	head = try_get_compound_head(pud_page(orig), refs);
-	if (!head) {
-		*nr -= refs;
+	if (!head)
 		return 0;
-	}
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
-		*nr -= refs;
-		while (refs--)
-			put_page(head);
+		put_compound_head(head, refs);
 		return 0;
 	}
 
-	SetPageReferenced(head);
+	__huge_pt_done(head, refs, nr);
 	return 1;
 }
 
@@ -2151,29 +2146,20 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 		return 0;
 
 	BUILD_BUG_ON(pgd_devmap(orig));
-	refs = 0;
+
 	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
-	do {
-		pages[*nr] = page;
-		(*nr)++;
-		page++;
-		refs++;
-	} while (addr += PAGE_SIZE, addr != end);
+	refs = __record_subpages(page, addr, end, pages, *nr);
 
 	head = try_get_compound_head(pgd_page(orig), refs);
-	if (!head) {
-		*nr -= refs;
+	if (!head)
 		return 0;
-	}
 
 	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
-		*nr -= refs;
-		while (refs--)
-			put_page(head);
+		put_compound_head(head, refs);
 		return 0;
 	}
 
-	SetPageReferenced(head);
+	__huge_pt_done(head, refs, nr);
 	return 1;
 }
 
-- 
2.24.0

[PATCH v4 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues

[John Hubbard]

An upcoming patch uses try_get_compound_head() more widely,
so move it to the top of gup.c.

Also fix a tiny spelling error and a checkpatch.pl warning.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 199da99e8ffc..933524de6249 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,6 +29,21 @@ struct follow_page_context {
 	unsigned int page_mask;
 };
 
+/*
+ * Return the compound head page with ref appropriately incremented,
+ * or NULL if that failed.
+ */
+static inline struct page *try_get_compound_head(struct page *page, int refs)
+{
+	struct page *head = compound_head(page);
+
+	if (WARN_ON_ONCE(page_ref_count(head) < 0))
+		return NULL;
+	if (unlikely(!page_cache_add_speculative(head, refs)))
+		return NULL;
+	return head;
+}
+
 /**
  * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
  * @pages:  array of pages to be maybe marked dirty, and definitely released.
@@ -1793,20 +1808,6 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
 	}
 }
 
-/*
- * Return the compund head page with ref appropriately incremented,
- * or NULL if that failed.
- */
-static inline struct page *try_get_compound_head(struct page *page, int refs)
-{
-	struct page *head = compound_head(page);
-	if (WARN_ON_ONCE(page_ref_count(head) < 0))
-		return NULL;
-	if (unlikely(!page_cache_add_speculative(head, refs)))
-		return NULL;
-	return head;
-}
-
 #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 			 unsigned int flags, struct page **pages, int *nr)
-- 
2.24.0

[PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[John Hubbard]

An upcoming patch changes and complicates the refcounting and
especially the "put page" aspects of it. In order to keep
everything clean, refactor the devmap page release routines:

* Rename put_devmap_managed_page() to page_is_devmap_managed(),
  and limit the functionality to "read only": return a bool,
  with no side effects.

* Add a new routine, put_devmap_managed_page(), to handle checking
  what kind of page it is, and what kind of refcount handling it
  requires.

* Rename __put_devmap_managed_page() to free_devmap_managed_page(),
  and limit the functionality to unconditionally freeing a devmap
  page.

This is originally based on a separate patch by Ira Weiny, which
applied to an early version of the put_user_page() experiments.
Since then, Jérôme Glisse suggested the refactoring described above.

Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h | 27 ++++++++++++++++---
 mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
 2 files changed, 53 insertions(+), 41 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a2adf95b3f9c..96228376139c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
 #endif
 
 #ifdef CONFIG_DEV_PAGEMAP_OPS
-void __put_devmap_managed_page(struct page *page);
+void free_devmap_managed_page(struct page *page);
 DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
-static inline bool put_devmap_managed_page(struct page *page)
+
+static inline bool page_is_devmap_managed(struct page *page)
 {
 	if (!static_branch_unlikely(&devmap_managed_key))
 		return false;
@@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
 	switch (page->pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
 	case MEMORY_DEVICE_FS_DAX:
-		__put_devmap_managed_page(page);
 		return true;
 	default:
 		break;
@@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
 	return false;
 }
 
+static inline bool put_devmap_managed_page(struct page *page)
+{
+	bool is_devmap = page_is_devmap_managed(page);
+
+	if (is_devmap) {
+		int count = page_ref_dec_return(page);
+
+		/*
+		 * devmap page refcounts are 1-based, rather than 0-based: if
+		 * refcount is 1, then the page is free and the refcount is
+		 * stable because nobody holds a reference on the page.
+		 */
+		if (count == 1)
+			free_devmap_managed_page(page);
+		else if (!count)
+			__put_page(page);
+	}
+
+	return is_devmap;
+}
+
 #else /* CONFIG_DEV_PAGEMAP_OPS */
 static inline bool put_devmap_managed_page(struct page *page)
 {
diff --git a/mm/memremap.c b/mm/memremap.c
index 03ccbdfeb697..bc7e2a27d025 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
 EXPORT_SYMBOL_GPL(get_dev_pagemap);
 
 #ifdef CONFIG_DEV_PAGEMAP_OPS
-void __put_devmap_managed_page(struct page *page)
+void free_devmap_managed_page(struct page *page)
 {
-	int count = page_ref_dec_return(page);
+	/* Clear Active bit in case of parallel mark_page_accessed */
+	__ClearPageActive(page);
+	__ClearPageWaiters(page);
+
+	mem_cgroup_uncharge(page);
 
 	/*
-	 * If refcount is 1 then page is freed and refcount is stable as nobody
-	 * holds a reference on the page.
+	 * When a device_private page is freed, the page->mapping field
+	 * may still contain a (stale) mapping value. For example, the
+	 * lower bits of page->mapping may still identify the page as
+	 * an anonymous page. Ultimately, this entire field is just
+	 * stale and wrong, and it will cause errors if not cleared.
+	 * One example is:
+	 *
+	 *  migrate_vma_pages()
+	 *    migrate_vma_insert_page()
+	 *      page_add_new_anon_rmap()
+	 *        __page_set_anon_rmap()
+	 *          ...checks page->mapping, via PageAnon(page) call,
+	 *            and incorrectly concludes that the page is an
+	 *            anonymous page. Therefore, it incorrectly,
+	 *            silently fails to set up the new anon rmap.
+	 *
+	 * For other types of ZONE_DEVICE pages, migration is either
+	 * handled differently or not done at all, so there is no need
+	 * to clear page->mapping.
 	 */
-	if (count == 1) {
-		/* Clear Active bit in case of parallel mark_page_accessed */
-		__ClearPageActive(page);
-		__ClearPageWaiters(page);
-
-		mem_cgroup_uncharge(page);
-
-		/*
-		 * When a device_private page is freed, the page->mapping field
-		 * may still contain a (stale) mapping value. For example, the
-		 * lower bits of page->mapping may still identify the page as
-		 * an anonymous page. Ultimately, this entire field is just
-		 * stale and wrong, and it will cause errors if not cleared.
-		 * One example is:
-		 *
-		 *  migrate_vma_pages()
-		 *    migrate_vma_insert_page()
-		 *      page_add_new_anon_rmap()
-		 *        __page_set_anon_rmap()
-		 *          ...checks page->mapping, via PageAnon(page) call,
-		 *            and incorrectly concludes that the page is an
-		 *            anonymous page. Therefore, it incorrectly,
-		 *            silently fails to set up the new anon rmap.
-		 *
-		 * For other types of ZONE_DEVICE pages, migration is either
-		 * handled differently or not done at all, so there is no need
-		 * to clear page->mapping.
-		 */
-		if (is_device_private_page(page))
-			page->mapping = NULL;
+	if (is_device_private_page(page))
+		page->mapping = NULL;
 
-		page->pgmap->ops->page_free(page);
-	} else if (!count)
-		__put_page(page);
+	page->pgmap->ops->page_free(page);
 }
-EXPORT_SYMBOL(__put_devmap_managed_page);
+EXPORT_SYMBOL(free_devmap_managed_page);
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
-- 
2.24.0

[PATCH v4 05/23] goldish_pipe: rename local pin_user_pages() routine

[John Hubbard]

1. Avoid naming conflicts: rename local static function from
"pin_user_pages()" to "pin_goldfish_pages()".

An upcoming patch will introduce a global pin_user_pages()
function.

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/platform/goldfish/goldfish_pipe.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
index cef0133aa47a..7ed2a21a0bac 100644
--- a/drivers/platform/goldfish/goldfish_pipe.c
+++ b/drivers/platform/goldfish/goldfish_pipe.c
@@ -257,12 +257,12 @@ static int goldfish_pipe_error_convert(int status)
 	}
 }
 
-static int pin_user_pages(unsigned long first_page,
-			  unsigned long last_page,
-			  unsigned int last_page_size,
-			  int is_write,
-			  struct page *pages[MAX_BUFFERS_PER_COMMAND],
-			  unsigned int *iter_last_page_size)
+static int pin_goldfish_pages(unsigned long first_page,
+			      unsigned long last_page,
+			      unsigned int last_page_size,
+			      int is_write,
+			      struct page *pages[MAX_BUFFERS_PER_COMMAND],
+			      unsigned int *iter_last_page_size)
 {
 	int ret;
 	int requested_pages = ((last_page - first_page) >> PAGE_SHIFT) + 1;
@@ -354,9 +354,9 @@ static int transfer_max_buffers(struct goldfish_pipe *pipe,
 	if (mutex_lock_interruptible(&pipe->lock))
 		return -ERESTARTSYS;
 
-	pages_count = pin_user_pages(first_page, last_page,
-				     last_page_size, is_write,
-				     pipe->pages, &iter_last_page_size);
+	pages_count = pin_goldfish_pages(first_page, last_page,
+					 last_page_size, is_write,
+					 pipe->pages, &iter_last_page_size);
 	if (pages_count < 0) {
 		mutex_unlock(&pipe->lock);
 		return pages_count;
-- 
2.24.0

[PATCH v4 06/23] IB/umem: use get_user_pages_fast() to pin DMA pages

[John Hubbard]

And get rid of the mmap_sem calls, as part of that. Note
that get_user_pages_fast() will, if necessary, fall back to
__gup_longterm_unlocked(), which takes the mmap_sem as needed.

Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/infiniband/core/umem.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 24244a2f68cc..3d664a2539eb 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -271,16 +271,13 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
 	sg = umem->sg_head.sgl;
 
 	while (npages) {
-		down_read(&mm->mmap_sem);
-		ret = get_user_pages(cur_base,
-				     min_t(unsigned long, npages,
-					   PAGE_SIZE / sizeof (struct page *)),
-				     gup_flags | FOLL_LONGTERM,
-				     page_list, NULL);
-		if (ret < 0) {
-			up_read(&mm->mmap_sem);
+		ret = get_user_pages_fast(cur_base,
+					  min_t(unsigned long, npages,
+						PAGE_SIZE /
+						sizeof(struct page *)),
+					  gup_flags | FOLL_LONGTERM, page_list);
+		if (ret < 0)
 			goto umem_release;
-		}
 
 		cur_base += ret * PAGE_SIZE;
 		npages   -= ret;
@@ -288,8 +285,6 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
 		sg = ib_umem_add_sg_table(sg, page_list, ret,
 			dma_get_max_seg_size(context->device->dma_device),
 			&umem->sg_nents);
-
-		up_read(&mm->mmap_sem);
 	}
 
 	sg_mark_end(sg);
-- 
2.24.0

[PATCH v4 07/23] media/v4l2-core: set pages dirty upon releasing DMA buffers

[John Hubbard]

After DMA is complete, and the device and CPU caches are synchronized,
it's still required to mark the CPU pages as dirty, if the data was
coming from the device. However, this driver was just issuing a
bare put_page() call, without any set_page_dirty*() call.

Fix the problem, by calling set_page_dirty_lock() if the CPU pages
were potentially receiving data from the device.

Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/media/v4l2-core/videobuf-dma-sg.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
index 66a6c6c236a7..28262190c3ab 100644
--- a/drivers/media/v4l2-core/videobuf-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
@@ -349,8 +349,11 @@ int videobuf_dma_free(struct videobuf_dmabuf *dma)
 	BUG_ON(dma->sglen);
 
 	if (dma->pages) {
-		for (i = 0; i < dma->nr_pages; i++)
+		for (i = 0; i < dma->nr_pages; i++) {
+			if (dma->direction == DMA_FROM_DEVICE)
+				set_page_dirty_lock(dma->pages[i]);
 			put_page(dma->pages[i]);
+		}
 		kfree(dma->pages);
 		dma->pages = NULL;
 	}
-- 
2.24.0

[PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

[John Hubbard]

As it says in the updated comment in gup.c: current FOLL_LONGTERM
behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the
FS DAX check requirement on vmas.

However, the corresponding restriction in get_user_pages_remote() was
slightly stricter than is actually required: it forbade all
FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
that do not set the "locked" arg.

Update the code and comments accordingly, and update the VFIO caller
to take advantage of this, fixing a bug as a result: the VFIO caller
is logically a FOLL_LONGTERM user.

Also, remove an unnessary pair of calls that were releasing and
reacquiring the mmap_sem. There is no need to avoid holding mmap_sem
just in order to call page_to_pfn().

Also, move the DAX check ("if a VMA is DAX, don't allow long term
pinning") from the VFIO call site, all the way into the internals
of get_user_pages_remote() and __gup_longterm_locked(). That is:
get_user_pages_remote() calls __gup_longterm_locked(), which in turn
calls check_dax_vmas(). It's lightly explained in the comments as well.

Thanks to Jason Gunthorpe for pointing out a clean way to fix this,
and to Dan Williams for helping clarify the DAX refactoring.

Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/vfio/vfio_iommu_type1.c | 25 ++-----------------------
 mm/gup.c                        | 27 ++++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index d864277ea16f..7301b710c9a4 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
 {
 	struct page *page[1];
 	struct vm_area_struct *vma;
-	struct vm_area_struct *vmas[1];
 	unsigned int flags = 0;
 	int ret;
 
@@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
 		flags |= FOLL_WRITE;
 
 	down_read(&mm->mmap_sem);
-	if (mm == current->mm) {
-		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
-				     vmas);
-	} else {
-		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
-					    vmas, NULL);
-		/*
-		 * The lifetime of a vaddr_get_pfn() page pin is
-		 * userspace-controlled. In the fs-dax case this could
-		 * lead to indefinite stalls in filesystem operations.
-		 * Disallow attempts to pin fs-dax pages via this
-		 * interface.
-		 */
-		if (ret > 0 && vma_is_fsdax(vmas[0])) {
-			ret = -EOPNOTSUPP;
-			put_page(page[0]);
-		}
-	}
-	up_read(&mm->mmap_sem);
-
+	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
+				    page, NULL, NULL);
 	if (ret == 1) {
 		*pfn = page_to_pfn(page[0]);
 		return 0;
 	}
 
-	down_read(&mm->mmap_sem);
-
 	vaddr = untagged_addr(vaddr);
 
 	vma = find_vma_intersection(mm, vaddr, vaddr + 1);
diff --git a/mm/gup.c b/mm/gup.c
index 933524de6249..83702b2e86c8 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,6 +29,13 @@ struct follow_page_context {
 	unsigned int page_mask;
 };
 
+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 flags);
 /*
  * Return the compound head page with ref appropriately incremented,
  * or NULL if that failed.
@@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 		struct vm_area_struct **vmas, int *locked)
 {
 	/*
-	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+	 * Parts of FOLL_LONGTERM behavior are 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.
+	 * vmas. However, this only comes up if locked is set, and there are
+	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
+	 * allow what we can.
 	 */
-	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
-		return -EINVAL;
+	if (gup_flags & FOLL_LONGTERM) {
+		if (WARN_ON_ONCE(locked))
+			return -EINVAL;
+		/*
+		 * This will check the vmas (even if our vmas arg is NULL)
+		 * and return -ENOTSUPP if DAX isn't allowed in this case:
+		 */
+		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
+					     vmas, gup_flags | FOLL_TOUCH |
+					     FOLL_REMOTE);
+	}
 
 	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
 				       locked,
-- 
2.24.0

[PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[John Hubbard]

Introduce pin_user_pages*() variations of get_user_pages*() calls,
and also pin_longterm_pages*() variations.

These variants all set FOLL_PIN, which is also introduced, and
thoroughly documented.

The pin_longterm*() variants also set FOLL_LONGTERM, in addition
to FOLL_PIN:

    pin_user_pages()
    pin_user_pages_remote()
    pin_user_pages_fast()

    pin_longterm_pages()
    pin_longterm_pages_remote()
    pin_longterm_pages_fast()

All pages that are pinned via the above calls, must be unpinned via
put_user_page().

The underlying rules are:

* These are gup-internal flags, so the call sites should not directly
set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with
assertions, for the new FOLL_PIN flag. However, for the pre-existing
FOLL_LONGTERM flag, which has some call sites that still directly
set FOLL_LONGTERM, there is no assertion yet.

* Call sites that want to indicate that they are going to do DirectIO
  ("DIO") or something with similar characteristics, should call a
  get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers
  will:
        * Start with "pin_user_pages" instead of "get_user_pages". That
          makes it easy to find and audit the call sites.
        * Set FOLL_PIN

* For pages that are received via FOLL_PIN, those pages must be returned
  via put_user_page().

Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases
in this documentation. (I've reworded it and expanded upon it.)

Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>  # Documentation
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 Documentation/core-api/index.rst          |   1 +
 Documentation/core-api/pin_user_pages.rst | 218 +++++++++++++++++
 include/linux/mm.h                        |  75 +++++-
 mm/gup.c                                  | 275 ++++++++++++++++++++--
 4 files changed, 535 insertions(+), 34 deletions(-)
 create mode 100644 Documentation/core-api/pin_user_pages.rst

diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index ab0eae1c153a..413f7d7c8642 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -31,6 +31,7 @@ Core utilities
    generic-radix-tree
    memory-allocation
    mm-api
+   pin_user_pages
    gfp_mask-from-fs-io
    timekeeping
    boot-time-mm
diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
new file mode 100644
index 000000000000..ce819e709435
--- /dev/null
+++ b/Documentation/core-api/pin_user_pages.rst
@@ -0,0 +1,218 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====================================================
+pin_user_pages() and related calls
+====================================================
+
+.. contents:: :local:
+
+Overview
+========
+
+This document describes the following functions: ::
+
+ pin_user_pages
+ pin_user_pages_fast
+ pin_user_pages_remote
+
+ pin_longterm_pages
+ pin_longterm_pages_fast
+ pin_longterm_pages_remote
+
+Basic description of FOLL_PIN
+=============================
+
+FOLL_PIN and FOLL_LONGTERM are flags that can be passed to the get_user_pages*()
+("gup") family of functions. FOLL_PIN has significant interactions and
+interdependencies with FOLL_LONGTERM, so both are covered here.
+
+Both FOLL_PIN and FOLL_LONGTERM are internal to gup, meaning that neither
+FOLL_PIN nor FOLL_LONGTERM should not appear at the gup call sites. This allows
+the associated wrapper functions  (pin_user_pages() and others) to set the
+correct combination of these flags, and to check for problems as well.
+
+FOLL_PIN and FOLL_GET are mutually exclusive for a given gup call. However,
+multiple threads and call sites are free to pin the same struct pages, via both
+FOLL_PIN and FOLL_GET. It's just the call site that needs to choose one or the
+other, not the struct page(s).
+
+The FOLL_PIN implementation is nearly the same as FOLL_GET, except that FOLL_PIN
+uses a different reference counting technique.
+
+FOLL_PIN is a prerequisite to FOLL_LONGTGERM. Another way of saying that is,
+FOLL_LONGTERM is a specific case, more restrictive case of FOLL_PIN.
+
+Which flags are set by each wrapper
+===================================
+
+Only FOLL_PIN and FOLL_LONGTERM are covered here. These flags are added to
+whatever flags the caller provides::
+
+ Function                    gup flags (FOLL_PIN or FOLL_LONGTERM only)
+ --------                    ------------------------------------------
+ pin_user_pages              FOLL_PIN
+ pin_user_pages_fast         FOLL_PIN
+ pin_user_pages_remote       FOLL_PIN
+
+ pin_longterm_pages          FOLL_PIN | FOLL_LONGTERM
+ pin_longterm_pages_fast     FOLL_PIN | FOLL_LONGTERM
+ pin_longterm_pages_remote   FOLL_PIN | FOLL_LONGTERM
+
+Tracking dma-pinned pages
+=========================
+
+Some of the key design constraints, and solutions, for tracking dma-pinned
+pages:
+
+* An actual reference count, per struct page, is required. This is because
+  multiple processes may pin and unpin a page.
+
+* False positives (reporting that a page is dma-pinned, when in fact it is not)
+  are acceptable, but false negatives are not.
+
+* struct page may not be increased in size for this, and all fields are already
+  used.
+
+* Given the above, we can overload the page->_refcount field by using, sort of,
+  the upper bits in that field for a dma-pinned count. "Sort of", means that,
+  rather than dividing page->_refcount into bit fields, we simple add a medium-
+  large value (GUP_PIN_COUNTING_BIAS, initially chosen to be 1024: 10 bits) to
+  page->_refcount. This provides fuzzy behavior: if a page has get_page() called
+  on it 1024 times, then it will appear to have a single dma-pinned count.
+  And again, that's acceptable.
+
+This also leads to limitations: there are only 31-10==21 bits available for a
+counter that increments 10 bits at a time.
+
+TODO: for 1GB and larger huge pages, this is cutting it close. That's because
+when pin_user_pages() follows such pages, it increments the head page by "1"
+(where "1" used to mean "+1" for get_user_pages(), but now means "+1024" for
+pin_user_pages()) for each tail page. So if you have a 1GB huge page:
+
+* There are 256K (18 bits) worth of 4 KB tail pages.
+* There are 21 bits available to count up via GUP_PIN_COUNTING_BIAS (that is,
+  10 bits at a time)
+* There are 21 - 18 == 3 bits available to count. Except that there aren't,
+  because you need to allow for a few normal get_page() calls on the head page,
+  as well. Fortunately, the approach of using addition, rather than "hard"
+  bitfields, within page->_refcount, allows for sharing these bits gracefully.
+  But we're still looking at about 8 references.
+
+This, however, is a missing feature more than anything else, because it's easily
+solved by addressing an obvious inefficiency in the original get_user_pages()
+approach of retrieving pages: stop treating all the pages as if they were
+PAGE_SIZE. Retrieve huge pages as huge pages. The callers need to be aware of
+this, so some work is required. Once that's in place, this limitation mostly
+disappears from view, because there will be ample refcounting range available.
+
+* Callers must specifically request "dma-pinned tracking of pages". In other
+  words, just calling get_user_pages() will not suffice; a new set of functions,
+  pin_user_page() and related, must be used.
+
+FOLL_PIN, FOLL_GET, FOLL_LONGTERM: when to use which flags
+==========================================================
+
+Thanks to Jan Kara, Vlastimil Babka and several other -mm people, for describing
+these categories:
+
+CASE 1: Direct IO (DIO)
+-----------------------
+There are GUP references to pages that are serving
+as DIO buffers. These buffers are needed for a relatively short time (so they
+are not "long term"). No special synchronization with page_mkclean() or
+munmap() is provided. Therefore, flags to set at the call site are: ::
+
+    FOLL_PIN
+
+...but rather than setting FOLL_PIN directly, call sites should use one of
+the pin_user_pages*() routines that set FOLL_PIN.
+
+CASE 2: RDMA
+------------
+There are GUP references to pages that are serving as DMA
+buffers. These buffers are needed for a long time ("long term"). No special
+synchronization with page_mkclean() or munmap() is provided. Therefore, flags
+to set at the call site are: ::
+
+    FOLL_PIN | FOLL_LONGTERM
+
+NOTE: Some pages, such as DAX pages, cannot be pinned with longterm pins. That's
+because DAX pages do not have a separate page cache, and so "pinning" implies
+locking down file system blocks, which is not (yet) supported in that way.
+
+CASE 3: Hardware with page faulting support
+-------------------------------------------
+Here, a well-written driver doesn't normally need to pin pages at all. However,
+if the driver does choose to do so, it can register MMU notifiers for the range,
+and will be called back upon invalidation. Either way (avoiding page pinning, or
+using MMU notifiers to unpin upon request), there is proper synchronization with
+both filesystem and mm (page_mkclean(), munmap(), etc).
+
+Therefore, neither flag needs to be set.
+
+In this case, ideally, neither get_user_pages() nor pin_user_pages() should be
+called. Instead, the software should be written so that it does not pin pages.
+This allows mm and filesystems to operate more efficiently and reliably.
+
+CASE 4: Pinning for struct page manipulation only
+-------------------------------------------------
+Here, normal GUP calls are sufficient, so neither flag needs to be set.
+
+page_dma_pinned(): the whole point of pinning
+=============================================
+
+The whole point of marking pages as "DMA-pinned" or "gup-pinned" is to be able
+to query, "is this page DMA-pinned?" That allows code such as page_mkclean()
+(and file system writeback code in general) to make informed decisions about
+what to do when a page cannot be unmapped due to such pins.
+
+What to do in those cases is the subject of a years-long series of discussions
+and debates (see the References at the end of this document). It's a TODO item
+here: fill in the details once that's worked out. Meanwhile, it's safe to say
+that having this available: ::
+
+        static inline bool page_dma_pinned(struct page *page)
+
+...is a prerequisite to solving the long-running gup+DMA problem.
+
+Another way of thinking about FOLL_GET, FOLL_PIN, and FOLL_LONGTERM
+===================================================================
+
+Another way of thinking about these flags is as a progression of restrictions:
+FOLL_GET is for struct page manipulation, without affecting the data that the
+struct page refers to. FOLL_PIN is a *replacement* for FOLL_GET, and is for
+short term pins on pages whose data *will* get accessed. As such, FOLL_PIN is
+a "more severe" form of pinning. And finally, FOLL_LONGTERM is an even more
+restrictive case that has FOLL_PIN as a prerequisite: this is for pages that
+will be pinned longterm, and whose data will be accessed.
+
+Unit testing
+============
+This file::
+
+ tools/testing/selftests/vm/gup_benchmark.c
+
+has the following new calls to exercise the new pin*() wrapper functions:
+
+* PIN_FAST_BENCHMARK (./gup_benchmark -a)
+* PIN_LONGTERM_BENCHMARK (./gup_benchmark -a)
+* PIN_BENCHMARK (./gup_benchmark -a)
+
+You can monitor how many total dma-pinned pages have been acquired and released
+since the system was booted, via two new /proc/vmstat entries: ::
+
+    /proc/vmstat/nr_foll_pin_requested
+    /proc/vmstat/nr_foll_pin_requested
+
+Those are both going to show zero, unless CONFIG_DEBUG_VM is set. This is
+because there is a noticeable performance drop in put_user_page(), when they
+are activated.
+
+References
+==========
+
+* `Some slow progress on get_user_pages() (Apr 2, 2019) <https://lwn.net/Articles/784574/>`_
+* `DMA and get_user_pages() (LPC: Dec 12, 2018) <https://lwn.net/Articles/774411/>`_
+* `The trouble with get_user_pages() (Apr 30, 2018) <https://lwn.net/Articles/753027/>`_
+
+John Hubbard, October, 2019
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 96228376139c..c351e1b0b4b7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1075,16 +1075,15 @@ static inline void put_page(struct page *page)
  * put_user_page() - release a gup-pinned page
  * @page:            pointer to page to be released
  *
- * Pages that were pinned via get_user_pages*() must be released via
- * either put_user_page(), or one of the put_user_pages*() routines
- * below. This is so that eventually, pages that are pinned via
- * get_user_pages*() can be separately tracked and uniquely handled. In
- * particular, interactions with RDMA and filesystems need special
- * handling.
+ * Pages that were pinned via either pin_user_pages*() or pin_longterm_pages*()
+ * must be released via either put_user_page(), or one of the put_user_pages*()
+ * routines. This is so that eventually such pages can be separately tracked and
+ * uniquely handled. In particular, interactions with RDMA and filesystems need
+ * special handling.
  *
  * put_user_page() and put_page() are not interchangeable, despite this early
  * implementation that makes them look the same. put_user_page() calls must
- * be perfectly matched up with get_user_page() calls.
+ * be perfectly matched up with pin*() calls.
  */
 static inline void put_user_page(struct page *page)
 {
@@ -1542,9 +1541,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 			    unsigned long start, unsigned long nr_pages,
 			    unsigned int gup_flags, struct page **pages,
 			    struct vm_area_struct **vmas, int *locked);
+long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+			   unsigned long start, unsigned long nr_pages,
+			   unsigned int gup_flags, struct page **pages,
+			   struct vm_area_struct **vmas, int *locked);
+long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+			       unsigned long start, unsigned long nr_pages,
+			       unsigned int gup_flags, struct page **pages,
+			       struct vm_area_struct **vmas, int *locked);
 long get_user_pages(unsigned long start, unsigned long nr_pages,
 			    unsigned int gup_flags, struct page **pages,
 			    struct vm_area_struct **vmas);
+long pin_user_pages(unsigned long start, unsigned long nr_pages,
+		    unsigned int gup_flags, struct page **pages,
+		    struct vm_area_struct **vmas);
+long pin_longterm_pages(unsigned long start, unsigned long nr_pages,
+			unsigned int gup_flags, struct page **pages,
+			struct vm_area_struct **vmas);
 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 		    unsigned int gup_flags, struct page **pages, int *locked);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
@@ -1552,6 +1565,10 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 
 int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);
+int pin_user_pages_fast(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages);
+int pin_longterm_pages_fast(unsigned long start, int nr_pages,
+			    unsigned int gup_flags, struct page **pages);
 
 int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc);
 int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
@@ -2610,13 +2627,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 #define FOLL_ANON	0x8000	/* don't do file mappings */
 #define FOLL_LONGTERM	0x10000	/* mapping lifetime is indefinite: see below */
 #define FOLL_SPLIT_PMD	0x20000	/* split huge pmd before returning */
+#define FOLL_PIN	0x40000	/* pages must be released via put_user_page() */
 
 /*
- * NOTE on FOLL_LONGTERM:
+ * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
+ * other. Here is what they mean, and how to use them:
  *
  * 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.
+ * period _often_ under userspace control.  This is in contrast to
+ * 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
@@ -2631,11 +2650,41 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
  * 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
+ * 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
+ * In the CMA case: long term 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.
+ *
+ * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount,
+ * but an additional pin counting system) will be invoked. This is intended for
+ * anything that gets a page reference and then touches page data (for example,
+ * Direct IO). This lets the filesystem know that some non-file-system entity is
+ * potentially changing the pages' data. In contrast to FOLL_GET (whose pages
+ * are released via put_page()), FOLL_PIN pages must be released, ultimately, by
+ * a call to put_user_page().
+ *
+ * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different
+ * and separate refcounting mechanisms, however, and that means that each has
+ * its own acquire and release mechanisms:
+ *
+ *     FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
+ *
+ *     FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and
+ *               put_user_pages to release.
+ *
+ * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call.
+ * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based
+ * calls applied to them, and that's perfectly OK. This is a constraint on the
+ * callers, not on the pages.)
+ *
+ * FOLL_PIN and FOLL_LONGTERM should be set internally by the pin_user_page*()
+ * and pin_longterm_*() APIs, never directly by the caller. That's in order to
+ * help avoid mismatches when releasing pages: get_user_pages*() pages must be
+ * released via put_page(), while pin_user_pages*() pages must be released via
+ * put_user_page().
+ *
+ * Please see Documentation/vm/pin_user_pages.rst for more information.
  */
 
 static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
diff --git a/mm/gup.c b/mm/gup.c
index 83702b2e86c8..4409e84dff51 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -201,6 +201,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	spinlock_t *ptl;
 	pte_t *ptep, pte;
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return ERR_PTR(-EINVAL);
 retry:
 	if (unlikely(pmd_bad(*pmd)))
 		return no_page_table(vma, flags);
@@ -812,7 +816,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 
 	start = untagged_addr(start);
 
-	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
+	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
 	/*
 	 * If FOLL_FORCE is set then do not force a full fault as the hinting
@@ -1036,7 +1040,16 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		BUG_ON(*locked != 1);
 	}
 
-	if (pages)
+	/*
+	 * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
+	 * is to set FOLL_GET if the caller wants pages[] filled in (but has
+	 * carelessly failed to specify FOLL_GET), so keep doing that, but only
+	 * for FOLL_GET, not for the newer FOLL_PIN.
+	 *
+	 * FOLL_PIN always expects pages to be non-null, but no need to assert
+	 * that here, as any failures will be obvious enough.
+	 */
+	if (pages && !(flags & FOLL_PIN))
 		flags |= FOLL_GET;
 
 	pages_done = 0;
@@ -1173,6 +1186,14 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 		unsigned int gup_flags, struct page **pages,
 		struct vm_area_struct **vmas, int *locked)
 {
+	/*
+	 * FOLL_PIN must only be set internally by the pin_user_page*() and
+	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
+	 * with an assertion:
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+		return -EINVAL;
+
 	/*
 	 * Parts of FOLL_LONGTERM behavior are incompatible with
 	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
@@ -1640,6 +1661,14 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
 		struct vm_area_struct **vmas)
 {
+	/*
+	 * FOLL_PIN must only be set internally by the pin_user_page*() and
+	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
+	 * with an assertion:
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+		return -EINVAL;
+
 	return __gup_longterm_locked(current, current->mm, start, nr_pages,
 				     pages, vmas, gup_flags | FOLL_TOUCH);
 }
@@ -2391,29 +2420,14 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
 	return ret;
 }
 
-/**
- * get_user_pages_fast() - pin user pages in memory
- * @start:	starting user address
- * @nr_pages:	number of pages from start to pin
- * @gup_flags:	flags modifying pin behaviour
- * @pages:	array that receives pointers to the pages pinned.
- *		Should be at least nr_pages long.
- *
- * Attempt to pin user pages in memory without taking mm->mmap_sem.
- * If not successful, it will fall back to taking the lock and
- * calling get_user_pages().
- *
- * Returns number of pages pinned. This may be fewer than the number
- * 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,
-			unsigned int gup_flags, struct page **pages)
+static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
+					unsigned int gup_flags,
+					struct page **pages)
 {
 	unsigned long addr, len, end;
 	int nr = 0, ret = 0;
 
-	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
+	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | FOLL_PIN)))
 		return -EINVAL;
 
 	start = untagged_addr(start) & PAGE_MASK;
@@ -2453,4 +2467,223 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 
 	return ret;
 }
+
+/**
+ * get_user_pages_fast() - pin user pages in memory
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @gup_flags:	flags modifying pin behaviour
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long.
+ *
+ * Attempt to pin user pages in memory without taking mm->mmap_sem.
+ * If not successful, it will fall back to taking the lock and
+ * calling get_user_pages().
+ *
+ * Returns number of pages pinned. This may be fewer than the number 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,
+			unsigned int gup_flags, struct page **pages)
+{
+	/*
+	 * FOLL_PIN must only be set internally by the pin_user_page*() and
+	 * pin_longterm_*() APIs, never directly by the caller, so enforce that:
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+		return -EINVAL;
+
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
 EXPORT_SYMBOL_GPL(get_user_pages_fast);
+
+/**
+ * pin_user_pages_fast() - pin user pages in memory without taking locks
+ *
+ * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
+ * get_user_pages_fast() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for further details.
+ *
+ * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
+ * is NOT intended for Case 2 (RDMA: long-term pins).
+ */
+int pin_user_pages_fast(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
+EXPORT_SYMBOL_GPL(pin_user_pages_fast);
+
+/**
+ * pin_longterm_pages_fast() - pin user pages in memory without taking locks
+ *
+ * Nearly the same as get_user_pages_fast(), except that FOLL_PIN and
+ * FOLL_LONGTERM are set. See get_user_pages_fast() for documentation on the
+ * function arguments, because the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for further details.
+ *
+ * FOLL_LONGTERM means that the pages are being pinned for "long term" use,
+ * typically by a non-CPU device, and we cannot be sure that waiting for a
+ * pinned page to become unpin will be effective.
+ *
+ * This is intended for Case 2 (RDMA: long-term pins) of the FOLL_PIN
+ * documentation.
+ */
+int pin_longterm_pages_fast(unsigned long start, int nr_pages,
+			    unsigned int gup_flags, struct page **pages)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= (FOLL_PIN | FOLL_LONGTERM);
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
+EXPORT_SYMBOL_GPL(pin_longterm_pages_fast);
+
+/**
+ * pin_user_pages_remote() - pin pages of a remote process (task != current)
+ *
+ * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
+ * get_user_pages_remote() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for details.
+ *
+ * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
+ * is NOT intended for Case 2 (RDMA: long-term pins).
+ */
+long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+			   unsigned long start, unsigned long nr_pages,
+			   unsigned int gup_flags, struct page **pages,
+			   struct vm_area_struct **vmas, int *locked)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN;
+
+	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
+				       locked, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages_remote);
+
+/**
+ * pin_longterm_pages_remote() - pin pages of a remote process (task != current)
+ *
+ * Nearly the same as get_user_pages_remote(), but note that FOLL_TOUCH is not
+ * set, and FOLL_PIN and FOLL_LONGTERM are set. See get_user_pages_remote() for
+ * documentation on the function arguments, because the arguments here are
+ * identical.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for further details.
+ *
+ * FOLL_LONGTERM means that the pages are being pinned for "long term" use,
+ * typically by a non-CPU device, and we cannot be sure that waiting for a
+ * pinned page to become unpin will be effective.
+ *
+ * This is intended for Case 2 (RDMA: long-term pins) in
+ * Documentation/vm/pin_user_pages.rst.
+ */
+long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
+			       unsigned long start, unsigned long nr_pages,
+			       unsigned int gup_flags, struct page **pages,
+			       struct vm_area_struct **vmas, int *locked)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	/*
+	 * Parts of FOLL_LONGTERM behavior are incompatible with
+	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+	 * vmas. However, this only comes up if locked is set, and there are
+	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
+	 * allow what we can.
+	 */
+	if (WARN_ON_ONCE(locked))
+		return -EINVAL;
+
+	gup_flags |= FOLL_LONGTERM | FOLL_REMOTE | FOLL_PIN;
+
+	/*
+	 * This will check the vmas (even if our vmas arg is NULL)
+	 * and return -ENOTSUPP if DAX isn't allowed in this case:
+	 */
+	return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
+				     vmas, gup_flags | FOLL_TOUCH |
+				     FOLL_REMOTE);
+}
+EXPORT_SYMBOL(pin_longterm_pages_remote);
+
+/**
+ * pin_user_pages() - pin user pages in memory for use by other devices
+ *
+ * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
+ * FOLL_PIN is set.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for details.
+ *
+ * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
+ * is NOT intended for Case 2 (RDMA: long-term pins).
+ */
+long pin_user_pages(unsigned long start, unsigned long nr_pages,
+		    unsigned int gup_flags, struct page **pages,
+		    struct vm_area_struct **vmas)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return __gup_longterm_locked(current, current->mm, start, nr_pages,
+				     pages, vmas, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages);
+
+/**
+ * pin_longterm_pages() - pin user pages in memory for long-term use (RDMA,
+ * typically)
+ *
+ * Nearly the same as get_user_pages(), except that FOLL_PIN and FOLL_LONGTERM
+ * are set. See get_user_pages_fast() for documentation on the function
+ * arguments, because the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via put_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for further details.
+ *
+ * FOLL_LONGTERM means that the pages are being pinned for "long term" use,
+ * typically by a non-CPU device, and we cannot be sure that waiting for a
+ * pinned page to become unpin will be effective.
+ *
+ * This is intended for Case 2 (RDMA: long-term pins) in
+ * Documentation/vm/pin_user_pages.rst.
+ */
+long pin_longterm_pages(unsigned long start, unsigned long nr_pages,
+			unsigned int gup_flags, struct page **pages,
+			struct vm_area_struct **vmas)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN | FOLL_LONGTERM;
+	return __gup_longterm_locked(current, current->mm, start, nr_pages,
+				     pages, vmas, gup_flags);
+}
+EXPORT_SYMBOL(pin_longterm_pages);
-- 
2.24.0

[PATCH v4 10/23] goldish_pipe: convert to pin_user_pages() and put_user_page()

[John Hubbard]

1. Call the new global pin_user_pages_fast(), from pin_goldfish_pages().

2. As required by pin_user_pages(), release these pages via
put_user_page(). In this case, do so via put_user_pages_dirty_lock().

That has the side effect of calling set_page_dirty_lock(), instead
of set_page_dirty(). This is probably more accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

Another side effect is that the release code is simplified because
the page[] loop is now in gup.c instead of here, so just delete the
local release_user_pages() entirely, and call
put_user_pages_dirty_lock() directly, instead.

[1] https://lore.kernel.org/r/20190723153640.GB720@lst.de

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/platform/goldfish/goldfish_pipe.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
index 7ed2a21a0bac..635a8bc1b480 100644
--- a/drivers/platform/goldfish/goldfish_pipe.c
+++ b/drivers/platform/goldfish/goldfish_pipe.c
@@ -274,7 +274,7 @@ static int pin_goldfish_pages(unsigned long first_page,
 		*iter_last_page_size = last_page_size;
 	}
 
-	ret = get_user_pages_fast(first_page, requested_pages,
+	ret = pin_user_pages_fast(first_page, requested_pages,
 				  !is_write ? FOLL_WRITE : 0,
 				  pages);
 	if (ret <= 0)
@@ -285,18 +285,6 @@ static int pin_goldfish_pages(unsigned long first_page,
 	return ret;
 }
 
-static void release_user_pages(struct page **pages, int pages_count,
-			       int is_write, s32 consumed_size)
-{
-	int i;
-
-	for (i = 0; i < pages_count; i++) {
-		if (!is_write && consumed_size > 0)
-			set_page_dirty(pages[i]);
-		put_page(pages[i]);
-	}
-}
-
 /* Populate the call parameters, merging adjacent pages together */
 static void populate_rw_params(struct page **pages,
 			       int pages_count,
@@ -372,7 +360,8 @@ static int transfer_max_buffers(struct goldfish_pipe *pipe,
 
 	*consumed_size = pipe->command_buffer->rw_params.consumed_size;
 
-	release_user_pages(pipe->pages, pages_count, is_write, *consumed_size);
+	put_user_pages_dirty_lock(pipe->pages, pages_count,
+				  !is_write && *consumed_size > 0);
 
 	mutex_unlock(&pipe->lock);
 	return 0;
-- 
2.24.0

[PATCH v4 11/23] IB/{core,hw,umem}: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*()

[John Hubbard]

Convert infiniband to use the new wrapper calls, and stop
explicitly setting FOLL_LONGTERM at the call sites.

The new pin_longterm_*() calls replace get_user_pages*()
calls, and set both FOLL_LONGTERM and a new FOLL_PIN
flag. The FOLL_PIN flag requires that the caller must
return the pages via put_user_page*() calls, but
infiniband was already doing that as part of an earlier
commit.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/infiniband/core/umem.c              | 10 +++++-----
 drivers/infiniband/core/umem_odp.c          | 13 ++++++-------
 drivers/infiniband/hw/hfi1/user_pages.c     |  4 ++--
 drivers/infiniband/hw/mthca/mthca_memfree.c |  3 +--
 drivers/infiniband/hw/qib/qib_user_pages.c  |  8 ++++----
 drivers/infiniband/hw/qib/qib_user_sdma.c   |  2 +-
 drivers/infiniband/hw/usnic/usnic_uiom.c    |  9 ++++-----
 drivers/infiniband/sw/siw/siw_mem.c         |  5 ++---
 8 files changed, 25 insertions(+), 29 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 3d664a2539eb..7f03f72e6dce 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -271,11 +271,11 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
 	sg = umem->sg_head.sgl;
 
 	while (npages) {
-		ret = get_user_pages_fast(cur_base,
-					  min_t(unsigned long, npages,
-						PAGE_SIZE /
-						sizeof(struct page *)),
-					  gup_flags | FOLL_LONGTERM, page_list);
+		ret = pin_longterm_pages_fast(cur_base,
+					      min_t(unsigned long, npages,
+						    PAGE_SIZE /
+						    sizeof(struct page *)),
+					      gup_flags, page_list);
 		if (ret < 0)
 			goto umem_release;
 
diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index 163ff7ba92b7..11249406148a 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -495,9 +495,8 @@ EXPORT_SYMBOL(ib_umem_odp_release);
  * The function returns -EFAULT if the DMA mapping operation fails. It returns
  * -EAGAIN if a concurrent invalidation prevents us from updating the page.
  *
- * The page is released via put_user_page even if the operation failed. For
- * on-demand pinning, the page is released whenever it isn't stored in the
- * umem.
+ * The page is released via put_page even if the operation failed. For on-demand
+ * pinning, the page is released whenever it isn't stored in the umem.
  */
 static int ib_umem_odp_map_dma_single_page(
 		struct ib_umem_odp *umem_odp,
@@ -542,7 +541,7 @@ static int ib_umem_odp_map_dma_single_page(
 	}
 
 out:
-	put_user_page(page);
+	put_page(page);
 
 	if (remove_existing_mapping) {
 		ib_umem_notifier_start_account(umem_odp);
@@ -665,7 +664,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
 					ret = -EFAULT;
 					break;
 				}
-				put_user_page(local_page_list[j]);
+				put_page(local_page_list[j]);
 				continue;
 			}
 
@@ -692,8 +691,8 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
 			 * ib_umem_odp_map_dma_single_page().
 			 */
 			if (npages - (j + 1) > 0)
-				put_user_pages(&local_page_list[j+1],
-					       npages - (j + 1));
+				release_pages(&local_page_list[j+1],
+					      npages - (j + 1));
 			break;
 		}
 	}
diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c
index 469acb961fbd..9b55b0a73e29 100644
--- a/drivers/infiniband/hw/hfi1/user_pages.c
+++ b/drivers/infiniband/hw/hfi1/user_pages.c
@@ -104,9 +104,9 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
 			    bool writable, struct page **pages)
 {
 	int ret;
-	unsigned int gup_flags = FOLL_LONGTERM | (writable ? FOLL_WRITE : 0);
+	unsigned int gup_flags = (writable ? FOLL_WRITE : 0);
 
-	ret = get_user_pages_fast(vaddr, npages, gup_flags, pages);
+	ret = pin_longterm_pages_fast(vaddr, npages, gup_flags, pages);
 	if (ret < 0)
 		return ret;
 
diff --git a/drivers/infiniband/hw/mthca/mthca_memfree.c b/drivers/infiniband/hw/mthca/mthca_memfree.c
index edccfd6e178f..beec7e4b8a96 100644
--- a/drivers/infiniband/hw/mthca/mthca_memfree.c
+++ b/drivers/infiniband/hw/mthca/mthca_memfree.c
@@ -472,8 +472,7 @@ int mthca_map_user_db(struct mthca_dev *dev, struct mthca_uar *uar,
 		goto out;
 	}
 
-	ret = get_user_pages_fast(uaddr & PAGE_MASK, 1,
-				  FOLL_WRITE | FOLL_LONGTERM, pages);
+	ret = pin_longterm_pages_fast(uaddr & PAGE_MASK, 1, FOLL_WRITE, pages);
 	if (ret < 0)
 		goto out;
 
diff --git a/drivers/infiniband/hw/qib/qib_user_pages.c b/drivers/infiniband/hw/qib/qib_user_pages.c
index 6bf764e41891..684a14e14d9b 100644
--- a/drivers/infiniband/hw/qib/qib_user_pages.c
+++ b/drivers/infiniband/hw/qib/qib_user_pages.c
@@ -108,10 +108,10 @@ int qib_get_user_pages(unsigned long start_page, size_t num_pages,
 
 	down_read(&current->mm->mmap_sem);
 	for (got = 0; got < num_pages; got += ret) {
-		ret = get_user_pages(start_page + got * PAGE_SIZE,
-				     num_pages - got,
-				     FOLL_LONGTERM | FOLL_WRITE | FOLL_FORCE,
-				     p + got, NULL);
+		ret = pin_longterm_pages(start_page + got * PAGE_SIZE,
+					 num_pages - got,
+					 FOLL_WRITE | FOLL_FORCE,
+					 p + got, NULL);
 		if (ret < 0) {
 			up_read(&current->mm->mmap_sem);
 			goto bail_release;
diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
index 05190edc2611..fd86a9d19370 100644
--- a/drivers/infiniband/hw/qib/qib_user_sdma.c
+++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
@@ -670,7 +670,7 @@ static int qib_user_sdma_pin_pages(const struct qib_devdata *dd,
 		else
 			j = npages;
 
-		ret = get_user_pages_fast(addr, j, FOLL_LONGTERM, pages);
+		ret = pin_longterm_pages_fast(addr, j, 0, pages);
 		if (ret != j) {
 			i = 0;
 			j = ret;
diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c
index 62e6ffa9ad78..6b90ca1c3771 100644
--- a/drivers/infiniband/hw/usnic/usnic_uiom.c
+++ b/drivers/infiniband/hw/usnic/usnic_uiom.c
@@ -141,11 +141,10 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
 	ret = 0;
 
 	while (npages) {
-		ret = get_user_pages(cur_base,
-				     min_t(unsigned long, npages,
-				     PAGE_SIZE / sizeof(struct page *)),
-				     gup_flags | FOLL_LONGTERM,
-				     page_list, NULL);
+		ret = pin_longterm_pages(cur_base,
+					 min_t(unsigned long, npages,
+					     PAGE_SIZE / sizeof(struct page *)),
+					 gup_flags, page_list, NULL);
 
 		if (ret < 0)
 			goto out;
diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
index e99983f07663..20e663d7ada8 100644
--- a/drivers/infiniband/sw/siw/siw_mem.c
+++ b/drivers/infiniband/sw/siw/siw_mem.c
@@ -426,9 +426,8 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
 		while (nents) {
 			struct page **plist = &umem->page_chunk[i].plist[got];
 
-			rv = get_user_pages(first_page_va, nents,
-					    foll_flags | FOLL_LONGTERM,
-					    plist, NULL);
+			rv = pin_longterm_pages(first_page_va, nents,
+						foll_flags, plist, NULL);
 			if (rv < 0)
 				goto out_sem_up;
 
-- 
2.24.0

[PATCH v4 12/23] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()

[John Hubbard]

Convert process_vm_access to use the new pin_user_pages_remote()
call, which sets FOLL_PIN. Setting FOLL_PIN is now required for
code that requires tracking of pinned pages.

Also, release the pages via put_user_page*().

Also, rename "pages" to "pinned_pages", as this makes for
easier reading of process_vm_rw_single_vec().

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/process_vm_access.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 357aa7bef6c0..fd20ab675b85 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -42,12 +42,11 @@ static int process_vm_rw_pages(struct page **pages,
 		if (copy > len)
 			copy = len;
 
-		if (vm_write) {
+		if (vm_write)
 			copied = copy_page_from_iter(page, offset, copy, iter);
-			set_page_dirty_lock(page);
-		} else {
+		else
 			copied = copy_page_to_iter(page, offset, copy, iter);
-		}
+
 		len -= copied;
 		if (copied < copy && iov_iter_count(iter))
 			return -EFAULT;
@@ -96,7 +95,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
 		flags |= FOLL_WRITE;
 
 	while (!rc && nr_pages && iov_iter_count(iter)) {
-		int pages = min(nr_pages, max_pages_per_loop);
+		int pinned_pages = min(nr_pages, max_pages_per_loop);
 		int locked = 1;
 		size_t bytes;
 
@@ -106,14 +105,15 @@ static int process_vm_rw_single_vec(unsigned long addr,
 		 * current/current->mm
 		 */
 		down_read(&mm->mmap_sem);
-		pages = get_user_pages_remote(task, mm, pa, pages, flags,
-					      process_pages, NULL, &locked);
+		pinned_pages = pin_user_pages_remote(task, mm, pa, pinned_pages,
+						     flags, process_pages,
+						     NULL, &locked);
 		if (locked)
 			up_read(&mm->mmap_sem);
-		if (pages <= 0)
+		if (pinned_pages <= 0)
 			return -EFAULT;
 
-		bytes = pages * PAGE_SIZE - start_offset;
+		bytes = pinned_pages * PAGE_SIZE - start_offset;
 		if (bytes > len)
 			bytes = len;
 
@@ -122,10 +122,12 @@ static int process_vm_rw_single_vec(unsigned long addr,
 					 vm_write);
 		len -= bytes;
 		start_offset = 0;
-		nr_pages -= pages;
-		pa += pages * PAGE_SIZE;
-		while (pages)
-			put_page(process_pages[--pages]);
+		nr_pages -= pinned_pages;
+		pa += pinned_pages * PAGE_SIZE;
+
+		/* If vm_write is set, the pages need to be made dirty: */
+		put_user_pages_dirty_lock(process_pages, pinned_pages,
+					  vm_write);
 	}
 
 	return rc;
-- 
2.24.0

[PATCH v4 13/23] drm/via: set FOLL_PIN via pin_user_pages_fast()

[John Hubbard]

Convert drm/via to use the new pin_user_pages_fast() call, which sets
FOLL_PIN. Setting FOLL_PIN is now required for code that requires
tracking of pinned pages, and therefore for any code that calls
put_user_page().

In partial anticipation of this work, the drm/via driver was already
calling put_user_page() instead of put_page(). Therefore, in order to
convert from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required
is to change get_user_pages() to pin_user_pages().

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/drm/via/via_dmablit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/via/via_dmablit.c b/drivers/gpu/drm/via/via_dmablit.c
index 3db000aacd26..37c5e572993a 100644
--- a/drivers/gpu/drm/via/via_dmablit.c
+++ b/drivers/gpu/drm/via/via_dmablit.c
@@ -239,7 +239,7 @@ via_lock_all_dma_pages(drm_via_sg_info_t *vsg,  drm_via_dmablit_t *xfer)
 	vsg->pages = vzalloc(array_size(sizeof(struct page *), vsg->num_pages));
 	if (NULL == vsg->pages)
 		return -ENOMEM;
-	ret = get_user_pages_fast((unsigned long)xfer->mem_addr,
+	ret = pin_user_pages_fast((unsigned long)xfer->mem_addr,
 			vsg->num_pages,
 			vsg->direction == DMA_FROM_DEVICE ? FOLL_WRITE : 0,
 			vsg->pages);
-- 
2.24.0

[PATCH v4 14/23] fs/io_uring: set FOLL_PIN via pin_user_pages()

[John Hubbard]

Convert fs/io_uring to use the new pin_user_pages() call, which sets
FOLL_PIN. Setting FOLL_PIN is now required for code that requires
tracking of pinned pages, and therefore for any code that calls
put_user_page().

In partial anticipation of this work, the io_uring code was already
calling put_user_page() instead of put_page(). Therefore, in order to
convert from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required
here is to change get_user_pages() to pin_longterm_pages().

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 fs/io_uring.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f9a38998f2fc..0f307f2c7cac 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3433,9 +3433,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
 
 		ret = 0;
 		down_read(&current->mm->mmap_sem);
-		pret = get_user_pages(ubuf, nr_pages,
-				      FOLL_WRITE | FOLL_LONGTERM,
-				      pages, vmas);
+		pret = pin_longterm_pages(ubuf, nr_pages, FOLL_WRITE, pages,
+					  vmas);
 		if (pret == nr_pages) {
 			/* don't support file backed memory */
 			for (j = 0; j < nr_pages; j++) {
-- 
2.24.0

[PATCH v4 15/23] net/xdp: set FOLL_PIN via pin_user_pages()

[John Hubbard]

Convert net/xdp to use the new pin_longterm_pages() call, which sets
FOLL_PIN. Setting FOLL_PIN is now required for code that requires
tracking of pinned pages.

In partial anticipation of this work, the net/xdp code was already
calling put_user_page() instead of put_page(). Therefore, in order to
convert from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required
here is to change get_user_pages() to pin_longterm_pages().

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 net/xdp/xdp_umem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index 3049af269fbf..66c814863cfd 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c
@@ -291,8 +291,8 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem)
 		return -ENOMEM;
 
 	down_read(&current->mm->mmap_sem);
-	npgs = get_user_pages(umem->address, umem->npgs,
-			      gup_flags | FOLL_LONGTERM, &umem->pgs[0], NULL);
+	npgs = pin_longterm_pages(umem->address, umem->npgs, gup_flags,
+				  &umem->pgs[0], NULL);
 	up_read(&current->mm->mmap_sem);
 
 	if (npgs != umem->npgs) {
-- 
2.24.0

[PATCH v4 16/23] mm/gup: track FOLL_PIN pages

[John Hubbard]

Add tracking of pages that were pinned via FOLL_PIN.

As mentioned in the FOLL_PIN documentation, callers who effectively set
FOLL_PIN are required to ultimately free such pages via put_user_page().
The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET
for DIO and/or RDMA use".

Pages that have been pinned via FOLL_PIN are identifiable via a
new function call:

   bool page_dma_pinned(struct page *page);

What to do in response to encountering such a page, is left to later
patchsets. There is discussion about this in [1].

This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().

Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h       |  74 +++++++++++----
 include/linux/mmzone.h   |   2 +
 include/linux/page_ref.h |  10 +++
 mm/gup.c                 | 189 +++++++++++++++++++++++++++++++++------
 mm/huge_memory.c         |  54 ++++++++++-
 mm/hugetlb.c             |  39 +++++++-
 mm/vmstat.c              |   2 +
 7 files changed, 321 insertions(+), 49 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c351e1b0b4b7..19b3fa68a4da 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1054,6 +1054,8 @@ static inline __must_check bool try_get_page(struct page *page)
 	return true;
 }
 
+__must_check bool user_page_ref_inc(struct page *page);
+
 static inline void put_page(struct page *page)
 {
 	page = compound_head(page);
@@ -1071,30 +1073,70 @@ static inline void put_page(struct page *page)
 		__put_page(page);
 }
 
-/**
- * put_user_page() - release a gup-pinned page
- * @page:            pointer to page to be released
+/*
+ * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overload
+ * the page's refcount so that two separate items are tracked: the original page
+ * reference count, and also a new count of how many get_user_pages() calls were
+ * made against the page. ("gup-pinned" is another term for the latter).
+ *
+ * With this scheme, get_user_pages() becomes special: such pages are marked
+ * as distinct from normal pages. As such, the new put_user_page() call (and
+ * its variants) must be used in order to release gup-pinned pages.
+ *
+ * Choice of value:
  *
- * Pages that were pinned via either pin_user_pages*() or pin_longterm_pages*()
- * must be released via either put_user_page(), or one of the put_user_pages*()
- * routines. This is so that eventually such pages can be separately tracked and
- * uniquely handled. In particular, interactions with RDMA and filesystems need
- * special handling.
+ * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference
+ * counts with respect to get_user_pages() and put_user_page() becomes simpler,
+ * due to the fact that adding an even power of two to the page refcount has
+ * the effect of using only the upper N bits, for the code that counts up using
+ * the bias value. This means that the lower bits are left for the exclusive
+ * use of the original code that increments and decrements by one (or at least,
+ * by much smaller values than the bias value).
  *
- * put_user_page() and put_page() are not interchangeable, despite this early
- * implementation that makes them look the same. put_user_page() calls must
- * be perfectly matched up with pin*() calls.
+ * Of course, once the lower bits overflow into the upper bits (and this is
+ * OK, because subtraction recovers the original values), then visual inspection
+ * no longer suffices to directly view the separate counts. However, for normal
+ * applications that don't have huge page reference counts, this won't be an
+ * issue.
+ *
+ * Locking: the lockless algorithm described in page_cache_get_speculative()
+ * and page_cache_gup_pin_speculative() provides safe operation for
+ * get_user_pages and page_mkclean and other calls that race to set up page
+ * table entries.
  */
-static inline void put_user_page(struct page *page)
-{
-	put_page(page);
-}
+#define GUP_PIN_COUNTING_BIAS (1UL << 10)
 
+void put_user_page(struct page *page);
 void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 			       bool make_dirty);
-
 void put_user_pages(struct page **pages, unsigned long npages);
 
+/**
+ * page_dma_pinned() - report if a page is pinned for DMA.
+ *
+ * This function checks if a page has been pinned via a call to
+ * pin_user_pages*() or pin_longterm_pages*().
+ *
+ * The return value is partially fuzzy: false is not fuzzy, because it means
+ * "definitely not pinned for DMA", but true means "probably pinned for DMA, but
+ * possibly a false positive due to having at least GUP_PIN_COUNTING_BIAS worth
+ * of normal page references".
+ *
+ * False positives are OK, because: a) it's unlikely for a page to get that many
+ * refcounts, and b) all the callers of this routine are expected to be able to
+ * deal gracefully with a false positive.
+ *
+ * For more information, please see Documentation/vm/pin_user_pages.rst.
+ *
+ * @page:	pointer to page to be queried.
+ * @Return:	True, if it is likely that the page has been "dma-pinned".
+ *		False, if the page is definitely not dma-pinned.
+ */
+static inline bool page_dma_pinned(struct page *page)
+{
+	return (page_ref_count(compound_head(page))) >= GUP_PIN_COUNTING_BIAS;
+}
+
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define SECTION_IN_PAGE_FLAGS
 #endif
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bda20282746b..0485cba38d23 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -244,6 +244,8 @@ enum node_stat_item {
 	NR_DIRTIED,		/* page dirtyings since bootup */
 	NR_WRITTEN,		/* page writings since bootup */
 	NR_KERNEL_MISC_RECLAIMABLE,	/* reclaimable non-slab kernel pages */
+	NR_FOLL_PIN_REQUESTED,	/* via: pin_user_page(), gup flag: FOLL_PIN */
+	NR_FOLL_PIN_RETURNED,	/* pages returned via put_user_page() */
 	NR_VM_NODE_STAT_ITEMS
 };
 
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 14d14beb1f7f..b9cbe553d1e7 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr)
 		__page_ref_mod(page, -nr);
 }
 
+static inline int page_ref_sub_return(struct page *page, int nr)
+{
+	int ret = atomic_sub_return(nr, &page->_refcount);
+
+	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+		__page_ref_mod(page, -nr);
+
+	return ret;
+}
+
 static inline void page_ref_inc(struct page *page)
 {
 	atomic_inc(&page->_refcount);
diff --git a/mm/gup.c b/mm/gup.c
index 4409e84dff51..82e7e4ce5027 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -51,6 +51,94 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
 	return head;
 }
 
+#ifdef CONFIG_DEBUG_VM
+static inline void __update_proc_vmstat(struct page *page,
+					enum node_stat_item item, int count)
+{
+	mod_node_page_state(page_pgdat(page), item, count);
+}
+#else
+static inline void __update_proc_vmstat(struct page *page,
+					enum node_stat_item item, int count)
+{
+}
+#endif
+
+/**
+ * user_page_ref_inc() - mark a page as being used by get_user_pages(FOLL_PIN).
+ *
+ * @page:	pointer to page to be marked
+ * @Return:	true for success, false for failure
+ */
+__must_check bool user_page_ref_inc(struct page *page)
+{
+	page = try_get_compound_head(page, GUP_PIN_COUNTING_BIAS);
+	if (!page)
+		return false;
+
+	__update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1);
+	return true;
+}
+
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+static bool __put_devmap_managed_user_page(struct page *page)
+{
+	bool is_devmap = page_is_devmap_managed(page);
+
+	if (is_devmap) {
+		int count = page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS);
+
+		__update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+		/*
+		 * devmap page refcounts are 1-based, rather than 0-based: if
+		 * refcount is 1, then the page is free and the refcount is
+		 * stable because nobody holds a reference on the page.
+		 */
+		if (count == 1)
+			free_devmap_managed_page(page);
+		else if (!count)
+			__put_page(page);
+	}
+
+	return is_devmap;
+}
+#else
+static bool __put_devmap_managed_user_page(struct page *page)
+{
+	return false;
+}
+#endif /* CONFIG_DEV_PAGEMAP_OPS */
+
+/**
+ * put_user_page() - release a dma-pinned page
+ * @page:            pointer to page to be released
+ *
+ * Pages that were pinned via either pin_user_pages*() or pin_longterm_pages*()
+ * must be released via either put_user_page(), or one of the put_user_pages*()
+ * routines. This is so that such pages can be separately tracked and uniquely
+ * handled. In particular, interactions with RDMA and filesystems need special
+ * handling.
+ */
+void put_user_page(struct page *page)
+{
+	page = compound_head(page);
+
+	/*
+	 * For devmap managed pages we need to catch refcount transition from
+	 * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
+	 * page is free and we need to inform the device driver through
+	 * callback. See include/linux/memremap.h and HMM for details.
+	 */
+	if (__put_devmap_managed_user_page(page))
+		return;
+
+	if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS))
+		__put_page(page);
+
+	__update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+}
+EXPORT_SYMBOL(put_user_page);
+
 /**
  * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
  * @pages:  array of pages to be maybe marked dirty, and definitely released.
@@ -237,10 +325,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	}
 
 	page = vm_normal_page(vma, address, pte);
-	if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
+	if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
 		/*
-		 * Only return device mapping pages in the FOLL_GET case since
-		 * they are only valid while holding the pgmap reference.
+		 * Only return device mapping pages in the FOLL_GET or FOLL_PIN
+		 * case since they are only valid while holding the pgmap
+		 * reference.
 		 */
 		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
 		if (*pgmap)
@@ -283,6 +372,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 			page = ERR_PTR(-ENOMEM);
 			goto out;
 		}
+	} else if (flags & FOLL_PIN) {
+		if (unlikely(!user_page_ref_inc(page))) {
+			page = ERR_PTR(-ENOMEM);
+			goto out;
+		}
 	}
 	if (flags & FOLL_TOUCH) {
 		if ((flags & FOLL_WRITE) &&
@@ -544,8 +638,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
 	/* make this handle hugepd */
 	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
 	if (!IS_ERR(page)) {
-		BUG_ON(flags & FOLL_GET);
-		return page;
+		WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
+		return NULL;
 	}
 
 	pgd = pgd_offset(mm, address);
@@ -1844,13 +1938,17 @@ static inline pte_t gup_get_pte(pte_t *ptep)
 #endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */
 
 static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
+					    unsigned int flags,
 					    struct page **pages)
 {
 	while ((*nr) - nr_start) {
 		struct page *page = pages[--(*nr)];
 
 		ClearPageReferenced(page);
-		put_page(page);
+		if (flags & FOLL_PIN)
+			put_user_page(page);
+		else
+			put_page(page);
 	}
 }
 
@@ -1883,7 +1981,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 
 			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
 			if (unlikely(!pgmap)) {
-				undo_dev_pagemap(nr, nr_start, pages);
+				undo_dev_pagemap(nr, nr_start, flags, pages);
 				goto pte_unmap;
 			}
 		} else if (pte_special(pte))
@@ -1892,9 +1990,15 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 		page = pte_page(pte);
 
-		head = try_get_compound_head(page, 1);
-		if (!head)
-			goto pte_unmap;
+		if (flags & FOLL_PIN) {
+			head = page;
+			if (unlikely(!user_page_ref_inc(head)))
+				goto pte_unmap;
+		} else {
+			head = try_get_compound_head(page, 1);
+			if (!head)
+				goto pte_unmap;
+		}
 
 		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
 			put_page(head);
@@ -1948,12 +2052,20 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 
 		pgmap = get_dev_pagemap(pfn, pgmap);
 		if (unlikely(!pgmap)) {
-			undo_dev_pagemap(nr, nr_start, pages);
+			undo_dev_pagemap(nr, nr_start, flags, pages);
 			return 0;
 		}
 		SetPageReferenced(page);
 		pages[*nr] = page;
-		get_page(page);
+
+		if (flags & FOLL_PIN) {
+			if (unlikely(!user_page_ref_inc(page))) {
+				undo_dev_pagemap(nr, nr_start, flags, pages);
+				return 0;
+			}
+		} else
+			get_page(page);
+
 		(*nr)++;
 		pfn++;
 	} while (addr += PAGE_SIZE, addr != end);
@@ -1975,7 +2087,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		return 0;
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
-		undo_dev_pagemap(nr, nr_start, pages);
+		undo_dev_pagemap(nr, nr_start, flags, pages);
 		return 0;
 	}
 	return 1;
@@ -1993,7 +2105,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 		return 0;
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
-		undo_dev_pagemap(nr, nr_start, pages);
+		undo_dev_pagemap(nr, nr_start, flags, pages);
 		return 0;
 	}
 	return 1;
@@ -2077,9 +2189,16 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
 	refs = __record_subpages(page, addr, end, pages, *nr);
 
-	head = try_get_compound_head(head, refs);
-	if (!head)
-		return 0;
+	if (flags & FOLL_PIN) {
+		head = page;
+		if (unlikely(!user_page_ref_inc(head)))
+			return 0;
+		head = page;
+	} else {
+		head = try_get_compound_head(head, refs);
+		if (!head)
+			return 0;
+	}
 
 	if (unlikely(pte_val(pte) != pte_val(*ptep))) {
 		put_compound_head(head, refs);
@@ -2136,9 +2255,15 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	refs = __record_subpages(page, addr, end, pages, *nr);
 
-	head = try_get_compound_head(pmd_page(orig), refs);
-	if (!head)
-		return 0;
+	if (flags & FOLL_PIN) {
+		head = page;
+		if (unlikely(!user_page_ref_inc(head)))
+			return 0;
+	} else {
+		head = try_get_compound_head(pmd_page(orig), refs);
+		if (!head)
+			return 0;
+	}
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
 		put_compound_head(head, refs);
@@ -2169,9 +2294,15 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 	refs = __record_subpages(page, addr, end, pages, *nr);
 
-	head = try_get_compound_head(pud_page(orig), refs);
-	if (!head)
-		return 0;
+	if (flags & FOLL_PIN) {
+		head = page;
+		if (unlikely(!user_page_ref_inc(head)))
+			return 0;
+	} else {
+		head = try_get_compound_head(pud_page(orig), refs);
+		if (!head)
+			return 0;
+	}
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
 		put_compound_head(head, refs);
@@ -2197,9 +2328,15 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
 	refs = __record_subpages(page, addr, end, pages, *nr);
 
-	head = try_get_compound_head(pgd_page(orig), refs);
-	if (!head)
-		return 0;
+	if (flags & FOLL_PIN) {
+		head = page;
+		if (unlikely(!user_page_ref_inc(head)))
+			return 0;
+	} else {
+		head = try_get_compound_head(pgd_page(orig), refs);
+		if (!head)
+			return 0;
+	}
 
 	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
 		put_compound_head(head, refs);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 13cc93785006..4010c269e9e5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -945,6 +945,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	 */
 	WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
 		return NULL;
 
@@ -960,7 +965,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	 * device mapped pages can only be returned if the
 	 * caller will manage the page reference count.
 	 */
-	if (!(flags & FOLL_GET))
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
 		return ERR_PTR(-EEXIST);
 
 	pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
@@ -968,7 +973,18 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	if (!*pgmap)
 		return ERR_PTR(-EFAULT);
 	page = pfn_to_page(pfn);
-	get_page(page);
+
+	if (flags & FOLL_GET)
+		get_page(page);
+	else if (flags & FOLL_PIN) {
+		/*
+		 * user_page_ref_inc() is not actually expected to fail here
+		 * because we hold the pmd lock so no one can unmap the pmd and
+		 * free the page that it points to.
+		 */
+		if (unlikely(!user_page_ref_inc(page)))
+			page = ERR_PTR(-EFAULT);
+	}
 
 	return page;
 }
@@ -1088,6 +1104,11 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	if (flags & FOLL_WRITE && !pud_write(*pud))
 		return NULL;
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 	if (pud_present(*pud) && pud_devmap(*pud))
 		/* pass */;
 	else
@@ -1099,8 +1120,10 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	/*
 	 * device mapped pages can only be returned if the
 	 * caller will manage the page reference count.
+	 *
+	 * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here:
 	 */
-	if (!(flags & FOLL_GET))
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
 		return ERR_PTR(-EEXIST);
 
 	pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
@@ -1108,7 +1131,18 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	if (!*pgmap)
 		return ERR_PTR(-EFAULT);
 	page = pfn_to_page(pfn);
-	get_page(page);
+
+	if (flags & FOLL_GET)
+		get_page(page);
+	else if (flags & FOLL_PIN) {
+		/*
+		 * user_page_ref_inc() is not actually expected to fail here
+		 * because we hold the pud lock so no one can unmap the pud and
+		 * free the page that it points to.
+		 */
+		if (unlikely(!user_page_ref_inc(page)))
+			page = ERR_PTR(-EFAULT);
+	}
 
 	return page;
 }
@@ -1522,8 +1556,20 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 skip_mlock:
 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
 	VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
+
 	if (flags & FOLL_GET)
 		get_page(page);
+	else if (flags & FOLL_PIN) {
+		/*
+		 * user_page_ref_inc() is not actually expected to fail here
+		 * because we hold the pmd lock so no one can unmap the pmd and
+		 * free the page that it points to.
+		 */
+		if (unlikely(!user_page_ref_inc(page))) {
+			WARN_ON_ONCE(1);
+			page = NULL;
+		}
+	}
 
 out:
 	return page;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b45a95363a84..5ee80eea25e5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4462,7 +4462,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 same_page:
 		if (pages) {
 			pages[i] = mem_map_offset(page, pfn_offset);
-			get_page(pages[i]);
+
+			if (flags & FOLL_GET)
+				get_page(pages[i]);
+			else if (flags & FOLL_PIN) {
+				/*
+				 * user_page_ref_inc() is not actually expected
+				 * to fail here because we hold the ptl.
+				 */
+				if (unlikely(!user_page_ref_inc(pages[i]))) {
+					spin_unlock(ptl);
+					remainder = 0;
+					err = -ENOMEM;
+					WARN_ON_ONCE(1);
+					break;
+				}
+			}
 		}
 
 		if (vmas)
@@ -5022,6 +5037,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	struct page *page = NULL;
 	spinlock_t *ptl;
 	pte_t pte;
+
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 retry:
 	ptl = pmd_lockptr(mm, pmd);
 	spin_lock(ptl);
@@ -5034,8 +5055,20 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	pte = huge_ptep_get((pte_t *)pmd);
 	if (pte_present(pte)) {
 		page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+
 		if (flags & FOLL_GET)
 			get_page(page);
+		else if (flags & FOLL_PIN) {
+			/*
+			 * user_page_ref_inc() is not actually expected to fail
+			 * here because we hold the ptl.
+			 */
+			if (unlikely(!user_page_ref_inc(page))) {
+				WARN_ON_ONCE(1);
+				page = NULL;
+				goto out;
+			}
+		}
 	} else {
 		if (is_hugetlb_entry_migration(pte)) {
 			spin_unlock(ptl);
@@ -5056,7 +5089,7 @@ struct page * __weak
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
 		pud_t *pud, int flags)
 {
-	if (flags & FOLL_GET)
+	if (flags & (FOLL_GET | FOLL_PIN))
 		return NULL;
 
 	return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
@@ -5065,7 +5098,7 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
 struct page * __weak
 follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags)
 {
-	if (flags & FOLL_GET)
+	if (flags & (FOLL_GET | FOLL_PIN))
 		return NULL;
 
 	return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a8222041bd44..fdad40ccde7b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1167,6 +1167,8 @@ const char * const vmstat_text[] = {
 	"nr_dirtied",
 	"nr_written",
 	"nr_kernel_misc_reclaimable",
+	"nr_foll_pin_requested",
+	"nr_foll_pin_returned",
 
 	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",
-- 
2.24.0

[PATCH v4 17/23] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion

[John Hubbard]

1. Change v4l2 from get_user_pages(FOLL_LONGTERM), to
pin_longterm_pages(), which sets both FOLL_LONGTERM and FOLL_PIN.

2. Because all FOLL_PIN-acquired pages must be released via
put_user_page(), also convert the put_page() call over to
put_user_pages_dirty_lock().

Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/media/v4l2-core/videobuf-dma-sg.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
index 28262190c3ab..9b9c5b37bf59 100644
--- a/drivers/media/v4l2-core/videobuf-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
@@ -183,12 +183,12 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma,
 	dprintk(1, "init user [0x%lx+0x%lx => %d pages]\n",
 		data, size, dma->nr_pages);
 
-	err = get_user_pages(data & PAGE_MASK, dma->nr_pages,
-			     flags | FOLL_LONGTERM, dma->pages, NULL);
+	err = pin_longterm_pages(data & PAGE_MASK, dma->nr_pages,
+				 flags, dma->pages, NULL);
 
 	if (err != dma->nr_pages) {
 		dma->nr_pages = (err >= 0) ? err : 0;
-		dprintk(1, "get_user_pages: err=%d [%d]\n", err,
+		dprintk(1, "pin_longterm_pages: err=%d [%d]\n", err,
 			dma->nr_pages);
 		return err < 0 ? err : -EINVAL;
 	}
@@ -349,11 +349,8 @@ int videobuf_dma_free(struct videobuf_dmabuf *dma)
 	BUG_ON(dma->sglen);
 
 	if (dma->pages) {
-		for (i = 0; i < dma->nr_pages; i++) {
-			if (dma->direction == DMA_FROM_DEVICE)
-				set_page_dirty_lock(dma->pages[i]);
-			put_page(dma->pages[i]);
-		}
+		put_user_pages_dirty_lock(dma->pages, dma->nr_pages,
+					  dma->direction == DMA_FROM_DEVICE);
 		kfree(dma->pages);
 		dma->pages = NULL;
 	}
-- 
2.24.0

[PATCH v4 18/23] vfio, mm: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion

[John Hubbard]

1. Change vfio from get_user_pages(FOLL_LONGTERM), to
pin_longterm_pages(), which sets both FOLL_LONGTERM and FOLL_PIN.

2. Because all FOLL_PIN-acquired pages must be released via
put_user_page(), also convert the put_page() call over to
put_user_pages().

Note that this effectively changes the code's behavior in
vfio_iommu_type1.c: put_pfn(): it now ultimately calls
set_page_dirty_lock(), instead of set_page_dirty(). This is
probably more accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

[1] https://lore.kernel.org/r/20190723153640.GB720@lst.de

Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/vfio/vfio_iommu_type1.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 7301b710c9a4..1603459805f1 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -327,9 +327,8 @@ static int put_pfn(unsigned long pfn, int prot)
 {
 	if (!is_invalid_reserved_pfn(pfn)) {
 		struct page *page = pfn_to_page(pfn);
-		if (prot & IOMMU_WRITE)
-			SetPageDirty(page);
-		put_page(page);
+
+		put_user_pages_dirty_lock(&page, 1, prot & IOMMU_WRITE);
 		return 1;
 	}
 	return 0;
@@ -347,8 +346,8 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
 		flags |= FOLL_WRITE;
 
 	down_read(&mm->mmap_sem);
-	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
-				    page, NULL, NULL);
+	ret = pin_longterm_pages_remote(NULL, mm, vaddr, 1, flags, page, NULL,
+					NULL);
 	if (ret == 1) {
 		*pfn = page_to_pfn(page[0]);
 		return 0;
-- 
2.24.0

[PATCH v4 19/23] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page()

[John Hubbard]

1. Convert from get_user_pages(FOLL_LONGTERM) to pin_longterm_pages().

2. As required by pin_user_pages(), release these pages via
put_user_page(). In this case, do so via put_user_pages_dirty_lock().

That has the side effect of calling set_page_dirty_lock(), instead
of set_page_dirty(). This is probably more accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

3. Release each page in mem->hpages[] (instead of mem->hpas[]), because
that is the array that pin_longterm_pages() filled in. This is more
accurate and should be a little safer from a maintenance point of
view.

[1] https://lore.kernel.org/r/20190723153640.GB720@lst.de

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 arch/powerpc/mm/book3s64/iommu_api.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
index 56cc84520577..69d79cb50d47 100644
--- a/arch/powerpc/mm/book3s64/iommu_api.c
+++ b/arch/powerpc/mm/book3s64/iommu_api.c
@@ -103,9 +103,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 	for (entry = 0; entry < entries; entry += chunk) {
 		unsigned long n = min(entries - entry, chunk);
 
-		ret = get_user_pages(ua + (entry << PAGE_SHIFT), n,
-				FOLL_WRITE | FOLL_LONGTERM,
-				mem->hpages + entry, NULL);
+		ret = pin_longterm_pages(ua + (entry << PAGE_SHIFT), n,
+					 FOLL_WRITE, mem->hpages + entry, NULL);
 		if (ret == n) {
 			pinned += n;
 			continue;
@@ -167,9 +166,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 	return 0;
 
 free_exit:
-	/* free the reference taken */
-	for (i = 0; i < pinned; i++)
-		put_page(mem->hpages[i]);
+	/* free the references taken */
+	put_user_pages(mem->hpages, pinned);
 
 	vfree(mem->hpas);
 	kfree(mem);
@@ -212,10 +210,9 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
 		if (!page)
 			continue;
 
-		if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
-			SetPageDirty(page);
+		put_user_pages_dirty_lock(&mem->hpages[i], 1,
+					  MM_IOMMU_TABLE_GROUP_PAGE_DIRTY);
 
-		put_page(page);
 		mem->hpas[i] = 0;
 	}
 }
-- 
2.24.0

[PATCH v4 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1"

[John Hubbard]

Fix the gup benchmark flags to use the symbolic FOLL_WRITE,
instead of a hard-coded "1" value.

Also, clean up the filtering of gup flags a little, by just doing
it once before issuing any of the get_user_pages*() calls. This
makes it harder to overlook, instead of having little "gup_flags & 1"
phrases in the function calls.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup_benchmark.c                         | 9 ++++++---
 tools/testing/selftests/vm/gup_benchmark.c | 6 +++++-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
index 7dd602d7f8db..7fc44d25eca7 100644
--- a/mm/gup_benchmark.c
+++ b/mm/gup_benchmark.c
@@ -48,18 +48,21 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 			nr = (next - addr) / PAGE_SIZE;
 		}
 
+		/* Filter out most gup flags: only allow a tiny subset here: */
+		gup->flags &= FOLL_WRITE;
+
 		switch (cmd) {
 		case GUP_FAST_BENCHMARK:
-			nr = get_user_pages_fast(addr, nr, gup->flags & 1,
+			nr = get_user_pages_fast(addr, nr, gup->flags,
 						 pages + i);
 			break;
 		case GUP_LONGTERM_BENCHMARK:
 			nr = get_user_pages(addr, nr,
-					    (gup->flags & 1) | FOLL_LONGTERM,
+					    gup->flags | FOLL_LONGTERM,
 					    pages + i, NULL);
 			break;
 		case GUP_BENCHMARK:
-			nr = get_user_pages(addr, nr, gup->flags & 1, pages + i,
+			nr = get_user_pages(addr, nr, gup->flags, pages + i,
 					    NULL);
 			break;
 		default:
diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
index 485cf06ef013..389327e9b30a 100644
--- a/tools/testing/selftests/vm/gup_benchmark.c
+++ b/tools/testing/selftests/vm/gup_benchmark.c
@@ -18,6 +18,9 @@
 #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
 #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
 
+/* Just the flags we need, copied from mm.h: */
+#define FOLL_WRITE	0x01	/* check pte is writable */
+
 struct gup_benchmark {
 	__u64 get_delta_usec;
 	__u64 put_delta_usec;
@@ -85,7 +88,8 @@ int main(int argc, char **argv)
 	}
 
 	gup.nr_pages_per_call = nr_pages;
-	gup.flags = write;
+	if (write)
+		gup.flags |= FOLL_WRITE;
 
 	fd = open("/sys/kernel/debug/gup_benchmark", O_RDWR);
 	if (fd == -1)
-- 
2.24.0

[PATCH v4 21/23] mm/gup_benchmark: support pin_user_pages() and related calls

[John Hubbard]

Up until now, gup_benchmark supported testing of the
following kernel functions:

* get_user_pages(): via the '-U' command line option
* get_user_pages_longterm(): via the '-L' command line option
* get_user_pages_fast(): as the default (no options required)

Add test coverage for the new corresponding pin_*() functions:

* pin_user_pages(): via the '-c' command line option
* pin_longterm_pages(): via the '-b' command line option
* pin_user_pages_fast(): via the '-a' command line option

Also, add an option for clarity: '-u' for what is now (still) the
default choice: get_user_pages_fast().

Also, for the three commands that set FOLL_PIN, verify that the pages
really are dma-pinned, via the new is_dma_pinned() routine.
Those commands are:

    PIN_FAST_BENCHMARK     : calls pin_user_pages_fast()
    PIN_LONGTERM_BENCHMARK : calls pin_longterm_pages()
    PIN_BENCHMARK          : calls pin_user_pages()

In between the calls to pin_*() and put_user_pages(),
check each page: if page_dma_pinned() returns false, then
WARN and return.

Do this outside of the benchmark timestamps, so that it doesn't
affect reported times.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup_benchmark.c                         | 73 ++++++++++++++++++++--
 tools/testing/selftests/vm/gup_benchmark.c | 23 ++++++-
 2 files changed, 90 insertions(+), 6 deletions(-)

diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
index 7fc44d25eca7..8f980d91dbf5 100644
--- a/mm/gup_benchmark.c
+++ b/mm/gup_benchmark.c
@@ -8,6 +8,9 @@
 #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
 #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
 #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
+#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
+#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
+#define PIN_BENCHMARK		_IOWR('g', 6, struct gup_benchmark)
 
 struct gup_benchmark {
 	__u64 get_delta_usec;
@@ -19,6 +22,44 @@ struct gup_benchmark {
 	__u64 expansion[10];	/* For future use */
 };
 
+static void put_back_pages(int cmd, struct page **pages, unsigned long nr_pages)
+{
+	int i;
+
+	switch (cmd) {
+	case GUP_FAST_BENCHMARK:
+	case GUP_LONGTERM_BENCHMARK:
+	case GUP_BENCHMARK:
+		for (i = 0; i < nr_pages; i++)
+			put_page(pages[i]);
+		break;
+
+	case PIN_FAST_BENCHMARK:
+	case PIN_LONGTERM_BENCHMARK:
+	case PIN_BENCHMARK:
+		put_user_pages(pages, nr_pages);
+		break;
+	}
+}
+
+static void verify_dma_pinned(int cmd, struct page **pages,
+			      unsigned long nr_pages)
+{
+	int i;
+
+	switch (cmd) {
+	case PIN_FAST_BENCHMARK:
+	case PIN_LONGTERM_BENCHMARK:
+	case PIN_BENCHMARK:
+		for (i = 0; i < nr_pages; i++) {
+			if (WARN(!page_dma_pinned(pages[i]),
+				 "pages[%d] is NOT dma-pinned\n", i))
+				break;
+		}
+		break;
+	}
+}
+
 static int __gup_benchmark_ioctl(unsigned int cmd,
 		struct gup_benchmark *gup)
 {
@@ -65,6 +106,18 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 			nr = get_user_pages(addr, nr, gup->flags, pages + i,
 					    NULL);
 			break;
+		case PIN_FAST_BENCHMARK:
+			nr = pin_user_pages_fast(addr, nr, gup->flags,
+						 pages + i);
+			break;
+		case PIN_LONGTERM_BENCHMARK:
+			nr = pin_longterm_pages(addr, nr, gup->flags, pages + i,
+						NULL);
+			break;
+		case PIN_BENCHMARK:
+			nr = pin_user_pages(addr, nr, gup->flags, pages + i,
+					    NULL);
+			break;
 		default:
 			return -1;
 		}
@@ -75,15 +128,22 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 	}
 	end_time = ktime_get();
 
+	/* Shifting the meaning of nr_pages: now it is actual number pinned: */
+	nr_pages = i;
+
 	gup->get_delta_usec = ktime_us_delta(end_time, start_time);
 	gup->size = addr - gup->addr;
 
+	/*
+	 * Take an un-benchmark-timed moment to verify DMA pinned
+	 * state: print a warning if any non-dma-pinned pages are found:
+	 */
+	verify_dma_pinned(cmd, pages, nr_pages);
+
 	start_time = ktime_get();
-	for (i = 0; i < nr_pages; i++) {
-		if (!pages[i])
-			break;
-		put_page(pages[i]);
-	}
+
+	put_back_pages(cmd, pages, nr_pages);
+
 	end_time = ktime_get();
 	gup->put_delta_usec = ktime_us_delta(end_time, start_time);
 
@@ -101,6 +161,9 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
 	case GUP_FAST_BENCHMARK:
 	case GUP_LONGTERM_BENCHMARK:
 	case GUP_BENCHMARK:
+	case PIN_FAST_BENCHMARK:
+	case PIN_LONGTERM_BENCHMARK:
+	case PIN_BENCHMARK:
 		break;
 	default:
 		return -EINVAL;
diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
index 389327e9b30a..03928e47a86f 100644
--- a/tools/testing/selftests/vm/gup_benchmark.c
+++ b/tools/testing/selftests/vm/gup_benchmark.c
@@ -18,6 +18,15 @@
 #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
 #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
 
+/*
+ * Similar to above, but use FOLL_PIN instead of FOLL_GET. This is done
+ * by calling pin_user_pages_fast(), pin_longterm_pages(), and pin_user_pages(),
+ * respectively.
+ */
+#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
+#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
+#define PIN_BENCHMARK		_IOWR('g', 6, struct gup_benchmark)
+
 /* Just the flags we need, copied from mm.h: */
 #define FOLL_WRITE	0x01	/* check pte is writable */
 
@@ -40,8 +49,17 @@ int main(int argc, char **argv)
 	char *file = "/dev/zero";
 	char *p;
 
-	while ((opt = getopt(argc, argv, "m:r:n:f:tTLUwSH")) != -1) {
+	while ((opt = getopt(argc, argv, "m:r:n:f:abctTLUuwSH")) != -1) {
 		switch (opt) {
+		case 'a':
+			cmd = PIN_FAST_BENCHMARK;
+			break;
+		case 'b':
+			cmd = PIN_LONGTERM_BENCHMARK;
+			break;
+		case 'c':
+			cmd = PIN_BENCHMARK;
+			break;
 		case 'm':
 			size = atoi(optarg) * MB;
 			break;
@@ -63,6 +81,9 @@ int main(int argc, char **argv)
 		case 'U':
 			cmd = GUP_BENCHMARK;
 			break;
+		case 'u':
+			cmd = GUP_FAST_BENCHMARK;
+			break;
 		case 'w':
 			write = 1;
 			break;
-- 
2.24.0

[PATCH v4 22/23] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage

[John Hubbard]

It's good to have basic unit test coverage of the new FOLL_PIN
behavior. Fortunately, the gup_benchmark unit test is extremely
fast (a few milliseconds), so adding it the the run_vmtests suite
is going to cause no noticeable change in running time.

So, add two new invocations to run_vmtests:

1) Run gup_benchmark with normal get_user_pages().

2) Run gup_benchmark with pin_user_pages(). This is much like
the first call, except that it sets FOLL_PIN.

Running these two in quick succession also provide a visual
comparison of the running times, which is convenient.

The new invocations are fairly early in the run_vmtests script,
because with test suites, it's usually preferable to put the
shorter, faster tests first, all other things being equal.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 tools/testing/selftests/vm/run_vmtests | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests
index 951c507a27f7..93e8dc9a7cad 100755
--- a/tools/testing/selftests/vm/run_vmtests
+++ b/tools/testing/selftests/vm/run_vmtests
@@ -104,6 +104,28 @@ echo "NOTE: The above hugetlb tests provide minimal coverage.  Use"
 echo "      https://github.com/libhugetlbfs/libhugetlbfs.git for"
 echo "      hugetlb regression testing."
 
+echo "--------------------------------------------"
+echo "running 'gup_benchmark -U' (normal/slow gup)"
+echo "--------------------------------------------"
+./gup_benchmark -U
+if [ $? -ne 0 ]; then
+	echo "[FAIL]"
+	exitcode=1
+else
+	echo "[PASS]"
+fi
+
+echo "------------------------------------------"
+echo "running gup_benchmark -c (pin_user_pages)"
+echo "------------------------------------------"
+./gup_benchmark -c
+if [ $? -ne 0 ]; then
+	echo "[FAIL]"
+	exitcode=1
+else
+	echo "[PASS]"
+fi
+
 echo "-------------------"
 echo "running userfaultfd"
 echo "-------------------"
-- 
2.24.0

[PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM)

[John Hubbard]

Now that all other kernel callers of get_user_pages(FOLL_LONGTERM)
have been converted to pin_longterm_pages(), lock it down:

1) Add an assertion to get_user_pages(), preventing callers from
   passing FOLL_LONGTERM (in addition to the existing assertion that
   prevents FOLL_PIN).

2) Remove the associated GUP_LONGTERM_BENCHMARK test.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c                                   | 8 ++++----
 mm/gup_benchmark.c                         | 9 +--------
 tools/testing/selftests/vm/gup_benchmark.c | 7 ++-----
 3 files changed, 7 insertions(+), 17 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 82e7e4ce5027..90f5f95ee7ac 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1756,11 +1756,11 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
 		struct vm_area_struct **vmas)
 {
 	/*
-	 * FOLL_PIN must only be set internally by the pin_user_page*() and
-	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
-	 * with an assertion:
+	 * FOLL_PIN and FOLL_LONGTERM must only be set internally by the
+	 * pin_user_page*() and pin_longterm_*() APIs, never directly by the
+	 * caller, so enforce that with an assertion:
 	 */
-	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_LONGTERM)))
 		return -EINVAL;
 
 	return __gup_longterm_locked(current, current->mm, start, nr_pages,
diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
index 8f980d91dbf5..679f0e6a0adb 100644
--- a/mm/gup_benchmark.c
+++ b/mm/gup_benchmark.c
@@ -6,7 +6,7 @@
 #include <linux/debugfs.h>
 
 #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
-#define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
+/* Command 2 has been deleted. */
 #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
 #define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
 #define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
@@ -28,7 +28,6 @@ static void put_back_pages(int cmd, struct page **pages, unsigned long nr_pages)
 
 	switch (cmd) {
 	case GUP_FAST_BENCHMARK:
-	case GUP_LONGTERM_BENCHMARK:
 	case GUP_BENCHMARK:
 		for (i = 0; i < nr_pages; i++)
 			put_page(pages[i]);
@@ -97,11 +96,6 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 			nr = get_user_pages_fast(addr, nr, gup->flags,
 						 pages + i);
 			break;
-		case GUP_LONGTERM_BENCHMARK:
-			nr = get_user_pages(addr, nr,
-					    gup->flags | FOLL_LONGTERM,
-					    pages + i, NULL);
-			break;
 		case GUP_BENCHMARK:
 			nr = get_user_pages(addr, nr, gup->flags, pages + i,
 					    NULL);
@@ -159,7 +153,6 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
 
 	switch (cmd) {
 	case GUP_FAST_BENCHMARK:
-	case GUP_LONGTERM_BENCHMARK:
 	case GUP_BENCHMARK:
 	case PIN_FAST_BENCHMARK:
 	case PIN_LONGTERM_BENCHMARK:
diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
index 03928e47a86f..836b7082db13 100644
--- a/tools/testing/selftests/vm/gup_benchmark.c
+++ b/tools/testing/selftests/vm/gup_benchmark.c
@@ -15,7 +15,7 @@
 #define PAGE_SIZE sysconf(_SC_PAGESIZE)
 
 #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
-#define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
+/* Command 2 has been deleted. */
 #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
 
 /*
@@ -49,7 +49,7 @@ int main(int argc, char **argv)
 	char *file = "/dev/zero";
 	char *p;
 
-	while ((opt = getopt(argc, argv, "m:r:n:f:abctTLUuwSH")) != -1) {
+	while ((opt = getopt(argc, argv, "m:r:n:f:abctTUuwSH")) != -1) {
 		switch (opt) {
 		case 'a':
 			cmd = PIN_FAST_BENCHMARK;
@@ -75,9 +75,6 @@ int main(int argc, char **argv)
 		case 'T':
 			thp = 0;
 			break;
-		case 'L':
-			cmd = GUP_LONGTERM_BENCHMARK;
-			break;
 		case 'U':
 			cmd = GUP_BENCHMARK;
 			break;
-- 
2.24.0

Re: [PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM

[John Hubbard]

On 11/12/19 8:26 PM, John Hubbard wrote:
> OK, here we go. Any VFIO and Infiniband runtime testing from anyone, is
> especially welcome here.
> 

Oh, and to make that easier, there is a git repo and branch, here:

    git@github.com:johnhubbard/linux.git pin_user_pages_tracking_v4


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[Jan Kara]

On Tue 12-11-19 20:26:56, John Hubbard wrote:
> Introduce pin_user_pages*() variations of get_user_pages*() calls,
> and also pin_longterm_pages*() variations.
> 
> These variants all set FOLL_PIN, which is also introduced, and
> thoroughly documented.
> 
> The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> to FOLL_PIN:
> 
>     pin_user_pages()
>     pin_user_pages_remote()
>     pin_user_pages_fast()
> 
>     pin_longterm_pages()
>     pin_longterm_pages_remote()
>     pin_longterm_pages_fast()
> 
> All pages that are pinned via the above calls, must be unpinned via
> put_user_page().
> 
> The underlying rules are:
> 
> * These are gup-internal flags, so the call sites should not directly
> set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with
> assertions, for the new FOLL_PIN flag. However, for the pre-existing
> FOLL_LONGTERM flag, which has some call sites that still directly
> set FOLL_LONGTERM, there is no assertion yet.
> 
> * Call sites that want to indicate that they are going to do DirectIO
>   ("DIO") or something with similar characteristics, should call a
>   get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers
>   will:
>         * Start with "pin_user_pages" instead of "get_user_pages". That
>           makes it easy to find and audit the call sites.
>         * Set FOLL_PIN
> 
> * For pages that are received via FOLL_PIN, those pages must be returned
>   via put_user_page().
> 
> Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases
> in this documentation. (I've reworded it and expanded upon it.)
> 
> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>  # Documentation
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Thanks for the documentation. It looks great!

> diff --git a/mm/gup.c b/mm/gup.c
> index 83702b2e86c8..4409e84dff51 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -201,6 +201,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
>  	spinlock_t *ptl;
>  	pte_t *ptep, pte;
>  
> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> +	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> +			 (FOLL_PIN | FOLL_GET)))
> +		return ERR_PTR(-EINVAL);
>  retry:
>  	if (unlikely(pmd_bad(*pmd)))
>  		return no_page_table(vma, flags);

How does FOLL_PIN result in grabbing (at least normal, for now) page reference?
I didn't find that anywhere in this patch but it is a prerequisite to
converting any user to pin_user_pages() interface, right?

> +/**
> + * pin_user_pages_fast() - pin user pages in memory without taking locks
> + *
> + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
> + * get_user_pages_fast() for documentation on the function arguments, because
> + * the arguments here are identical.
> + *
> + * FOLL_PIN means that the pages must be released via put_user_page(). Please
> + * see Documentation/vm/pin_user_pages.rst for further details.
> + *
> + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
> + * is NOT intended for Case 2 (RDMA: long-term pins).
> + */
> +int pin_user_pages_fast(unsigned long start, int nr_pages,
> +			unsigned int gup_flags, struct page **pages)
> +{
> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> +	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
> +		return -EINVAL;
> +
> +	gup_flags |= FOLL_PIN;
> +	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
> +}
> +EXPORT_SYMBOL_GPL(pin_user_pages_fast);

I was somewhat wondering about the number of functions you add here. So we
have:

pin_user_pages()
pin_user_pages_fast()
pin_user_pages_remote()

and then longterm variants:

pin_longterm_pages()
pin_longterm_pages_fast()
pin_longterm_pages_remote()

and obviously we have gup like:
get_user_pages()
get_user_pages_fast()
get_user_pages_remote()
... and some other gup variants ...

I think we really should have pin_* vs get_* variants as they are very
different in terms of guarantees and after conversion, any use of get_*
variant in non-mm code should be closely scrutinized. OTOH pin_longterm_*
don't look *that* useful to me and just using pin_* instead with
FOLL_LONGTERM flag would look OK to me and somewhat reduce the number of
functions which is already large enough? What do people think? I don't feel
too strongly about this but wanted to bring this up.

								Honza



-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Jan Kara]

On Tue 12-11-19 20:26:51, John Hubbard wrote:
> An upcoming patch changes and complicates the refcounting and
> especially the "put page" aspects of it. In order to keep
> everything clean, refactor the devmap page release routines:
> 
> * Rename put_devmap_managed_page() to page_is_devmap_managed(),
>   and limit the functionality to "read only": return a bool,
>   with no side effects.
> 
> * Add a new routine, put_devmap_managed_page(), to handle checking
>   what kind of page it is, and what kind of refcount handling it
>   requires.
> 
> * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
>   and limit the functionality to unconditionally freeing a devmap
>   page.
> 
> This is originally based on a separate patch by Ira Weiny, which
> applied to an early version of the put_user_page() experiments.
> Since then, Jérôme Glisse suggested the refactoring described above.
> 
> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  include/linux/mm.h | 27 ++++++++++++++++---
>  mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
>  2 files changed, 53 insertions(+), 41 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a2adf95b3f9c..96228376139c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
>  #endif
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page);
> +void free_devmap_managed_page(struct page *page);
>  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> -static inline bool put_devmap_managed_page(struct page *page)
> +
> +static inline bool page_is_devmap_managed(struct page *page)
>  {
>  	if (!static_branch_unlikely(&devmap_managed_key))
>  		return false;
> @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
>  	switch (page->pgmap->type) {
>  	case MEMORY_DEVICE_PRIVATE:
>  	case MEMORY_DEVICE_FS_DAX:
> -		__put_devmap_managed_page(page);
>  		return true;
>  	default:
>  		break;
> @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
>  	return false;
>  }
>  
> +static inline bool put_devmap_managed_page(struct page *page)
> +{
> +	bool is_devmap = page_is_devmap_managed(page);
> +
> +	if (is_devmap) {
> +		int count = page_ref_dec_return(page);
> +
> +		/*
> +		 * devmap page refcounts are 1-based, rather than 0-based: if
> +		 * refcount is 1, then the page is free and the refcount is
> +		 * stable because nobody holds a reference on the page.
> +		 */
> +		if (count == 1)
> +			free_devmap_managed_page(page);
> +		else if (!count)
> +			__put_page(page);
> +	}
> +
> +	return is_devmap;
> +}
> +
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
>  static inline bool put_devmap_managed_page(struct page *page)
>  {
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..bc7e2a27d025 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  EXPORT_SYMBOL_GPL(get_dev_pagemap);
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page)
> +void free_devmap_managed_page(struct page *page)
>  {
> -	int count = page_ref_dec_return(page);
> +	/* Clear Active bit in case of parallel mark_page_accessed */
> +	__ClearPageActive(page);
> +	__ClearPageWaiters(page);
> +
> +	mem_cgroup_uncharge(page);
>  
>  	/*
> -	 * If refcount is 1 then page is freed and refcount is stable as nobody
> -	 * holds a reference on the page.
> +	 * When a device_private page is freed, the page->mapping field
> +	 * may still contain a (stale) mapping value. For example, the
> +	 * lower bits of page->mapping may still identify the page as
> +	 * an anonymous page. Ultimately, this entire field is just
> +	 * stale and wrong, and it will cause errors if not cleared.
> +	 * One example is:
> +	 *
> +	 *  migrate_vma_pages()
> +	 *    migrate_vma_insert_page()
> +	 *      page_add_new_anon_rmap()
> +	 *        __page_set_anon_rmap()
> +	 *          ...checks page->mapping, via PageAnon(page) call,
> +	 *            and incorrectly concludes that the page is an
> +	 *            anonymous page. Therefore, it incorrectly,
> +	 *            silently fails to set up the new anon rmap.
> +	 *
> +	 * For other types of ZONE_DEVICE pages, migration is either
> +	 * handled differently or not done at all, so there is no need
> +	 * to clear page->mapping.
>  	 */
> -	if (count == 1) {
> -		/* Clear Active bit in case of parallel mark_page_accessed */
> -		__ClearPageActive(page);
> -		__ClearPageWaiters(page);
> -
> -		mem_cgroup_uncharge(page);
> -
> -		/*
> -		 * When a device_private page is freed, the page->mapping field
> -		 * may still contain a (stale) mapping value. For example, the
> -		 * lower bits of page->mapping may still identify the page as
> -		 * an anonymous page. Ultimately, this entire field is just
> -		 * stale and wrong, and it will cause errors if not cleared.
> -		 * One example is:
> -		 *
> -		 *  migrate_vma_pages()
> -		 *    migrate_vma_insert_page()
> -		 *      page_add_new_anon_rmap()
> -		 *        __page_set_anon_rmap()
> -		 *          ...checks page->mapping, via PageAnon(page) call,
> -		 *            and incorrectly concludes that the page is an
> -		 *            anonymous page. Therefore, it incorrectly,
> -		 *            silently fails to set up the new anon rmap.
> -		 *
> -		 * For other types of ZONE_DEVICE pages, migration is either
> -		 * handled differently or not done at all, so there is no need
> -		 * to clear page->mapping.
> -		 */
> -		if (is_device_private_page(page))
> -			page->mapping = NULL;
> +	if (is_device_private_page(page))
> +		page->mapping = NULL;
>  
> -		page->pgmap->ops->page_free(page);
> -	} else if (!count)
> -		__put_page(page);
> +	page->pgmap->ops->page_free(page);
>  }
> -EXPORT_SYMBOL(__put_devmap_managed_page);
> +EXPORT_SYMBOL(free_devmap_managed_page);
>  #endif /* CONFIG_DEV_PAGEMAP_OPS */
> -- 
> 2.24.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v4 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues

[Jan Kara]

On Tue 12-11-19 20:26:50, John Hubbard wrote:
> An upcoming patch uses try_get_compound_head() more widely,
> so move it to the top of gup.c.
> 
> Also fix a tiny spelling error and a checkpatch.pl warning.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  mm/gup.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 199da99e8ffc..933524de6249 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -29,6 +29,21 @@ struct follow_page_context {
>  	unsigned int page_mask;
>  };
>  
> +/*
> + * Return the compound head page with ref appropriately incremented,
> + * or NULL if that failed.
> + */
> +static inline struct page *try_get_compound_head(struct page *page, int refs)
> +{
> +	struct page *head = compound_head(page);
> +
> +	if (WARN_ON_ONCE(page_ref_count(head) < 0))
> +		return NULL;
> +	if (unlikely(!page_cache_add_speculative(head, refs)))
> +		return NULL;
> +	return head;
> +}
> +
>  /**
>   * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
>   * @pages:  array of pages to be maybe marked dirty, and definitely released.
> @@ -1793,20 +1808,6 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
>  	}
>  }
>  
> -/*
> - * Return the compund head page with ref appropriately incremented,
> - * or NULL if that failed.
> - */
> -static inline struct page *try_get_compound_head(struct page *page, int refs)
> -{
> -	struct page *head = compound_head(page);
> -	if (WARN_ON_ONCE(page_ref_count(head) < 0))
> -		return NULL;
> -	if (unlikely(!page_cache_add_speculative(head, refs)))
> -		return NULL;
> -	return head;
> -}
> -
>  #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
>  static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>  			 unsigned int flags, struct page **pages, int *nr)
> -- 
> 2.24.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v4 01/23] mm/gup: pass flags arg to __gup_device_* functions

[Jan Kara]

On Tue 12-11-19 20:26:48, John Hubbard wrote:
> A subsequent patch requires access to gup flags, so
> pass the flags argument through to the __gup_device_*
> functions.
> 
> Also placate checkpatch.pl by shortening a nearby line.
> 
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Looks good! You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  mm/gup.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 8f236a335ae9..85caf76b3012 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1890,7 +1890,8 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>  
>  #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
>  static int __gup_device_huge(unsigned long pfn, unsigned long addr,
> -		unsigned long end, struct page **pages, int *nr)
> +			     unsigned long end, unsigned int flags,
> +			     struct page **pages, int *nr)
>  {
>  	int nr_start = *nr;
>  	struct dev_pagemap *pgmap = NULL;
> @@ -1916,13 +1917,14 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
>  }
>  
>  static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> -		unsigned long end, struct page **pages, int *nr)
> +				 unsigned long end, unsigned int flags,
> +				 struct page **pages, int *nr)
>  {
>  	unsigned long fault_pfn;
>  	int nr_start = *nr;
>  
>  	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> -	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
> +	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
>  		return 0;
>  
>  	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> @@ -1933,13 +1935,14 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>  }
>  
>  static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> -		unsigned long end, struct page **pages, int *nr)
> +				 unsigned long end, unsigned int flags,
> +				 struct page **pages, int *nr)
>  {
>  	unsigned long fault_pfn;
>  	int nr_start = *nr;
>  
>  	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> -	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
> +	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
>  		return 0;
>  
>  	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> @@ -1950,14 +1953,16 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
>  }
>  #else
>  static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> -		unsigned long end, struct page **pages, int *nr)
> +				 unsigned long end, unsigned int flags,
> +				 struct page **pages, int *nr)
>  {
>  	BUILD_BUG();
>  	return 0;
>  }
>  
>  static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
> -		unsigned long end, struct page **pages, int *nr)
> +				 unsigned long end, unsigned int flags,
> +				 struct page **pages, int *nr)
>  {
>  	BUILD_BUG();
>  	return 0;
> @@ -2062,7 +2067,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>  	if (pmd_devmap(orig)) {
>  		if (unlikely(flags & FOLL_LONGTERM))
>  			return 0;
> -		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
> +		return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
> +					     pages, nr);
>  	}
>  
>  	refs = 0;
> @@ -2092,7 +2098,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>  }
>  
>  static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> -		unsigned long end, unsigned int flags, struct page **pages, int *nr)
> +			unsigned long end, unsigned int flags,
> +			struct page **pages, int *nr)
>  {
>  	struct page *head, *page;
>  	int refs;
> @@ -2103,7 +2110,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
>  	if (pud_devmap(orig)) {
>  		if (unlikely(flags & FOLL_LONGTERM))
>  			return 0;
> -		return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
> +		return __gup_device_huge_pud(orig, pudp, addr, end, flags,
> +					     pages, nr);
>  	}
>  
>  	refs = 0;
> -- 
> 2.24.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines

[Jan Kara]

On Tue 12-11-19 20:26:49, John Hubbard wrote:
> There are four locations in gup.c that have a fair amount of code
> duplication. This means that changing one requires making the same
> changes in four places, not to mention reading the same code four
> times, and wondering if there are subtle differences.
> 
> Factor out the common code into static functions, thus reducing the
> overall line count and the code's complexity.
> 
> Also, take the opportunity to slightly improve the efficiency of the
> error cases, by doing a mass subtraction of the refcount, surrounded
> by get_page()/put_page().
> 
> Also, further simplify (slightly), by waiting until the the successful
> end of each routine, to increment *nr.
> 
> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

> diff --git a/mm/gup.c b/mm/gup.c
> index 85caf76b3012..199da99e8ffc 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1969,6 +1969,34 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
>  }
>  #endif
>  
> +static int __record_subpages(struct page *page, unsigned long addr,
> +			     unsigned long end, struct page **pages, int nr)
> +{
> +	int nr_recorded_pages = 0;
> +
> +	do {
> +		pages[nr] = page;
> +		nr++;
> +		page++;
> +		nr_recorded_pages++;
> +	} while (addr += PAGE_SIZE, addr != end);
> +	return nr_recorded_pages;
> +}

Why don't you pass in already pages + nr?

> +
> +static void put_compound_head(struct page *page, int refs)
> +{
> +	/* Do a get_page() first, in case refs == page->_refcount */
> +	get_page(page);
> +	page_ref_sub(page, refs);
> +	put_page(page);
> +}
> +
> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
> +{
> +	*nr += nr_recorded_pages;
> +	SetPageReferenced(head);
> +}

I don't find this last helper very useful. It seems to muddy water more
than necessary...

Other than that the cleanup looks nice to me.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

[Jason Gunthorpe]

On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote:
> As it says in the updated comment in gup.c: current FOLL_LONGTERM
> behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the
> FS DAX check requirement on vmas.
> 
> However, the corresponding restriction in get_user_pages_remote() was
> slightly stricter than is actually required: it forbade all
> FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
> that do not set the "locked" arg.
> 
> Update the code and comments accordingly, and update the VFIO caller
> to take advantage of this, fixing a bug as a result: the VFIO caller
> is logically a FOLL_LONGTERM user.
> 
> Also, remove an unnessary pair of calls that were releasing and
> reacquiring the mmap_sem. There is no need to avoid holding mmap_sem
> just in order to call page_to_pfn().
> 
> Also, move the DAX check ("if a VMA is DAX, don't allow long term
> pinning") from the VFIO call site, all the way into the internals
> of get_user_pages_remote() and __gup_longterm_locked(). That is:
> get_user_pages_remote() calls __gup_longterm_locked(), which in turn
> calls check_dax_vmas(). It's lightly explained in the comments as well.
> 
> Thanks to Jason Gunthorpe for pointing out a clean way to fix this,
> and to Dan Williams for helping clarify the DAX refactoring.
> 
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Jerome Glisse <jglisse@redhat.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>  drivers/vfio/vfio_iommu_type1.c | 25 ++-----------------------
>  mm/gup.c                        | 27 ++++++++++++++++++++++-----
>  2 files changed, 24 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index d864277ea16f..7301b710c9a4 100644
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  {
>  	struct page *page[1];
>  	struct vm_area_struct *vma;
> -	struct vm_area_struct *vmas[1];
>  	unsigned int flags = 0;
>  	int ret;
>  
> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  		flags |= FOLL_WRITE;
>  
>  	down_read(&mm->mmap_sem);
> -	if (mm == current->mm) {
> -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
> -				     vmas);
> -	} else {
> -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
> -					    vmas, NULL);
> -		/*
> -		 * The lifetime of a vaddr_get_pfn() page pin is
> -		 * userspace-controlled. In the fs-dax case this could
> -		 * lead to indefinite stalls in filesystem operations.
> -		 * Disallow attempts to pin fs-dax pages via this
> -		 * interface.
> -		 */
> -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
> -			ret = -EOPNOTSUPP;
> -			put_page(page[0]);
> -		}
> -	}
> -	up_read(&mm->mmap_sem);
> -
> +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
> +				    page, NULL, NULL);
>  	if (ret == 1) {
>  		*pfn = page_to_pfn(page[0]);
>  		return 0;

Mind the return with the lock held this needs some goto unwind

Jason

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[Ira Weiny]

> > +/**
> > + * pin_user_pages_fast() - pin user pages in memory without taking locks
> > + *
> > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
> > + * get_user_pages_fast() for documentation on the function arguments, because
> > + * the arguments here are identical.
> > + *
> > + * FOLL_PIN means that the pages must be released via put_user_page(). Please
> > + * see Documentation/vm/pin_user_pages.rst for further details.
> > + *
> > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
> > + * is NOT intended for Case 2 (RDMA: long-term pins).
> > + */
> > +int pin_user_pages_fast(unsigned long start, int nr_pages,
> > +			unsigned int gup_flags, struct page **pages)
> > +{
> > +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > +	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
> > +		return -EINVAL;
> > +
> > +	gup_flags |= FOLL_PIN;
> > +	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
> > +}
> > +EXPORT_SYMBOL_GPL(pin_user_pages_fast);
> 
> I was somewhat wondering about the number of functions you add here. So we
> have:
> 
> pin_user_pages()
> pin_user_pages_fast()
> pin_user_pages_remote()
> 
> and then longterm variants:
> 
> pin_longterm_pages()
> pin_longterm_pages_fast()
> pin_longterm_pages_remote()
> 
> and obviously we have gup like:
> get_user_pages()
> get_user_pages_fast()
> get_user_pages_remote()
> ... and some other gup variants ...
> 
> I think we really should have pin_* vs get_* variants as they are very
> different in terms of guarantees and after conversion, any use of get_*
> variant in non-mm code should be closely scrutinized. OTOH pin_longterm_*
> don't look *that* useful to me and just using pin_* instead with
> FOLL_LONGTERM flag would look OK to me and somewhat reduce the number of
> functions which is already large enough? What do people think? I don't feel
> too strongly about this but wanted to bring this up.

I'm a bit concerned with the function explosion myself.  I think what you
suggest is a happy medium.  So I'd be ok with that.

Ira

Re: [PATCH v4 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:26:50PM -0800, John Hubbard wrote:
> An upcoming patch uses try_get_compound_head() more widely,
> so move it to the top of gup.c.
> 
> Also fix a tiny spelling error and a checkpatch.pl warning.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Simple enough...

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
>  mm/gup.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 199da99e8ffc..933524de6249 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -29,6 +29,21 @@ struct follow_page_context {
>  	unsigned int page_mask;
>  };
>  
> +/*
> + * Return the compound head page with ref appropriately incremented,
> + * or NULL if that failed.
> + */
> +static inline struct page *try_get_compound_head(struct page *page, int refs)
> +{
> +	struct page *head = compound_head(page);
> +
> +	if (WARN_ON_ONCE(page_ref_count(head) < 0))
> +		return NULL;
> +	if (unlikely(!page_cache_add_speculative(head, refs)))
> +		return NULL;
> +	return head;
> +}
> +
>  /**
>   * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
>   * @pages:  array of pages to be maybe marked dirty, and definitely released.
> @@ -1793,20 +1808,6 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
>  	}
>  }
>  
> -/*
> - * Return the compund head page with ref appropriately incremented,
> - * or NULL if that failed.
> - */
> -static inline struct page *try_get_compound_head(struct page *page, int refs)
> -{
> -	struct page *head = compound_head(page);
> -	if (WARN_ON_ONCE(page_ref_count(head) < 0))
> -		return NULL;
> -	if (unlikely(!page_cache_add_speculative(head, refs)))
> -		return NULL;
> -	return head;
> -}
> -
>  #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
>  static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>  			 unsigned int flags, struct page **pages, int *nr)
> -- 
> 2.24.0
> 

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[Dan Williams]

On Wed, Nov 13, 2019 at 2:43 AM Jan Kara <jack@suse.cz> wrote:
>
> On Tue 12-11-19 20:26:56, John Hubbard wrote:
> > Introduce pin_user_pages*() variations of get_user_pages*() calls,
> > and also pin_longterm_pages*() variations.
> >
> > These variants all set FOLL_PIN, which is also introduced, and
> > thoroughly documented.
> >
> > The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> > to FOLL_PIN:
> >
> >     pin_user_pages()
> >     pin_user_pages_remote()
> >     pin_user_pages_fast()
> >
> >     pin_longterm_pages()
> >     pin_longterm_pages_remote()
> >     pin_longterm_pages_fast()
> >
> > All pages that are pinned via the above calls, must be unpinned via
> > put_user_page().
> >
> > The underlying rules are:
> >
> > * These are gup-internal flags, so the call sites should not directly
> > set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with
> > assertions, for the new FOLL_PIN flag. However, for the pre-existing
> > FOLL_LONGTERM flag, which has some call sites that still directly
> > set FOLL_LONGTERM, there is no assertion yet.
> >
> > * Call sites that want to indicate that they are going to do DirectIO
> >   ("DIO") or something with similar characteristics, should call a
> >   get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers
> >   will:
> >         * Start with "pin_user_pages" instead of "get_user_pages". That
> >           makes it easy to find and audit the call sites.
> >         * Set FOLL_PIN
> >
> > * For pages that are received via FOLL_PIN, those pages must be returned
> >   via put_user_page().
> >
> > Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases
> > in this documentation. (I've reworded it and expanded upon it.)
> >
> > Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>  # Documentation
> > Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Jonathan Corbet <corbet@lwn.net>
> > Cc: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>
> Thanks for the documentation. It looks great!
>
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 83702b2e86c8..4409e84dff51 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -201,6 +201,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
> >       spinlock_t *ptl;
> >       pte_t *ptep, pte;
> >
> > +     /* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > +     if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> > +                      (FOLL_PIN | FOLL_GET)))
> > +             return ERR_PTR(-EINVAL);
> >  retry:
> >       if (unlikely(pmd_bad(*pmd)))
> >               return no_page_table(vma, flags);
>
> How does FOLL_PIN result in grabbing (at least normal, for now) page reference?
> I didn't find that anywhere in this patch but it is a prerequisite to
> converting any user to pin_user_pages() interface, right?
>
> > +/**
> > + * pin_user_pages_fast() - pin user pages in memory without taking locks
> > + *
> > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
> > + * get_user_pages_fast() for documentation on the function arguments, because
> > + * the arguments here are identical.
> > + *
> > + * FOLL_PIN means that the pages must be released via put_user_page(). Please
> > + * see Documentation/vm/pin_user_pages.rst for further details.
> > + *
> > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
> > + * is NOT intended for Case 2 (RDMA: long-term pins).
> > + */
> > +int pin_user_pages_fast(unsigned long start, int nr_pages,
> > +                     unsigned int gup_flags, struct page **pages)
> > +{
> > +     /* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > +     if (WARN_ON_ONCE(gup_flags & FOLL_GET))
> > +             return -EINVAL;
> > +
> > +     gup_flags |= FOLL_PIN;
> > +     return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
> > +}
> > +EXPORT_SYMBOL_GPL(pin_user_pages_fast);
>
> I was somewhat wondering about the number of functions you add here. So we
> have:
>
> pin_user_pages()
> pin_user_pages_fast()
> pin_user_pages_remote()
>
> and then longterm variants:
>
> pin_longterm_pages()
> pin_longterm_pages_fast()
> pin_longterm_pages_remote()
>
> and obviously we have gup like:
> get_user_pages()
> get_user_pages_fast()
> get_user_pages_remote()
> ... and some other gup variants ...
>
> I think we really should have pin_* vs get_* variants as they are very
> different in terms of guarantees and after conversion, any use of get_*
> variant in non-mm code should be closely scrutinized. OTOH pin_longterm_*
> don't look *that* useful to me and just using pin_* instead with
> FOLL_LONGTERM flag would look OK to me and somewhat reduce the number of
> functions which is already large enough? What do people think? I don't feel
> too strongly about this but wanted to bring this up.

I'd vote for FOLL_LONGTERM should obviate the need for
{get,pin}_user_pages_longterm(). It's a property that is passed by the
call site, not an internal flag.

Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote:
> As it says in the updated comment in gup.c: current FOLL_LONGTERM
> behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the
> FS DAX check requirement on vmas.
> 
> However, the corresponding restriction in get_user_pages_remote() was
> slightly stricter than is actually required: it forbade all
> FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
> that do not set the "locked" arg.
> 
> Update the code and comments accordingly, and update the VFIO caller
> to take advantage of this, fixing a bug as a result: the VFIO caller
> is logically a FOLL_LONGTERM user.
> 
> Also, remove an unnessary pair of calls that were releasing and
> reacquiring the mmap_sem. There is no need to avoid holding mmap_sem
> just in order to call page_to_pfn().
> 
> Also, move the DAX check ("if a VMA is DAX, don't allow long term
> pinning") from the VFIO call site, all the way into the internals
> of get_user_pages_remote() and __gup_longterm_locked(). That is:
> get_user_pages_remote() calls __gup_longterm_locked(), which in turn
> calls check_dax_vmas(). It's lightly explained in the comments as well.
> 
> Thanks to Jason Gunthorpe for pointing out a clean way to fix this,
> and to Dan Williams for helping clarify the DAX refactoring.
> 
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Jerome Glisse <jglisse@redhat.com>
> Cc: Ira Weiny <ira.weiny@intel.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 25 ++-----------------------
>  mm/gup.c                        | 27 ++++++++++++++++++++++-----
>  2 files changed, 24 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index d864277ea16f..7301b710c9a4 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  {
>  	struct page *page[1];
>  	struct vm_area_struct *vma;
> -	struct vm_area_struct *vmas[1];
>  	unsigned int flags = 0;
>  	int ret;
>  
> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  		flags |= FOLL_WRITE;
>  
>  	down_read(&mm->mmap_sem);
> -	if (mm == current->mm) {
> -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
> -				     vmas);
> -	} else {
> -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
> -					    vmas, NULL);
> -		/*
> -		 * The lifetime of a vaddr_get_pfn() page pin is
> -		 * userspace-controlled. In the fs-dax case this could
> -		 * lead to indefinite stalls in filesystem operations.
> -		 * Disallow attempts to pin fs-dax pages via this
> -		 * interface.
> -		 */
> -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
> -			ret = -EOPNOTSUPP;
> -			put_page(page[0]);
> -		}
> -	}
> -	up_read(&mm->mmap_sem);
> -
> +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
> +				    page, NULL, NULL);
>  	if (ret == 1) {
>  		*pfn = page_to_pfn(page[0]);
>  		return 0;
>  	}
>  
> -	down_read(&mm->mmap_sem);
> -
>  	vaddr = untagged_addr(vaddr);
>  
>  	vma = find_vma_intersection(mm, vaddr, vaddr + 1);
> diff --git a/mm/gup.c b/mm/gup.c
> index 933524de6249..83702b2e86c8 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -29,6 +29,13 @@ struct follow_page_context {
>  	unsigned int page_mask;
>  };
>  
> +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 flags);
>  /*
>   * Return the compound head page with ref appropriately incremented,
>   * or NULL if that failed.
> @@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>  		struct vm_area_struct **vmas, int *locked)
>  {
>  	/*
> -	 * FIXME: Current FOLL_LONGTERM behavior is incompatible with
> +	 * Parts of FOLL_LONGTERM behavior are 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.
> +	 * vmas. However, this only comes up if locked is set, and there are
> +	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
> +	 * allow what we can.
>  	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
> -		return -EINVAL;
> +	if (gup_flags & FOLL_LONGTERM) {
> +		if (WARN_ON_ONCE(locked))
> +			return -EINVAL;
> +		/*
> +		 * This will check the vmas (even if our vmas arg is NULL)
> +		 * and return -ENOTSUPP if DAX isn't allowed in this case:
> +		 */
> +		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
> +					     vmas, gup_flags | FOLL_TOUCH |
> +					     FOLL_REMOTE);
> +	}
>  
>  	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
>  				       locked,
> -- 
> 2.24.0
> 

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:26:56PM -0800, John Hubbard wrote:
> Introduce pin_user_pages*() variations of get_user_pages*() calls,
> and also pin_longterm_pages*() variations.
> 
> These variants all set FOLL_PIN, which is also introduced, and
> thoroughly documented.
> 
> The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> to FOLL_PIN:
> 
>     pin_user_pages()
>     pin_user_pages_remote()
>     pin_user_pages_fast()
> 
>     pin_longterm_pages()
>     pin_longterm_pages_remote()
>     pin_longterm_pages_fast()

At some point in this conversation I thought we were going to put in "unpin_*"
versions of these.

Is that still in the plans?

Ira

Re: [PATCH v4 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1"

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:27:07PM -0800, John Hubbard wrote:
> Fix the gup benchmark flags to use the symbolic FOLL_WRITE,
> instead of a hard-coded "1" value.
> 
> Also, clean up the filtering of gup flags a little, by just doing
> it once before issuing any of the get_user_pages*() calls. This
> makes it harder to overlook, instead of having little "gup_flags & 1"
> phrases in the function calls.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
>  mm/gup_benchmark.c                         | 9 ++++++---
>  tools/testing/selftests/vm/gup_benchmark.c | 6 +++++-
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 7dd602d7f8db..7fc44d25eca7 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -48,18 +48,21 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  			nr = (next - addr) / PAGE_SIZE;
>  		}
>  
> +		/* Filter out most gup flags: only allow a tiny subset here: */
> +		gup->flags &= FOLL_WRITE;
> +
>  		switch (cmd) {
>  		case GUP_FAST_BENCHMARK:
> -			nr = get_user_pages_fast(addr, nr, gup->flags & 1,
> +			nr = get_user_pages_fast(addr, nr, gup->flags,
>  						 pages + i);
>  			break;
>  		case GUP_LONGTERM_BENCHMARK:
>  			nr = get_user_pages(addr, nr,
> -					    (gup->flags & 1) | FOLL_LONGTERM,
> +					    gup->flags | FOLL_LONGTERM,
>  					    pages + i, NULL);
>  			break;
>  		case GUP_BENCHMARK:
> -			nr = get_user_pages(addr, nr, gup->flags & 1, pages + i,
> +			nr = get_user_pages(addr, nr, gup->flags, pages + i,
>  					    NULL);
>  			break;
>  		default:
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 485cf06ef013..389327e9b30a 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -18,6 +18,9 @@
>  #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
>  
> +/* Just the flags we need, copied from mm.h: */
> +#define FOLL_WRITE	0x01	/* check pte is writable */
> +
>  struct gup_benchmark {
>  	__u64 get_delta_usec;
>  	__u64 put_delta_usec;
> @@ -85,7 +88,8 @@ int main(int argc, char **argv)
>  	}
>  
>  	gup.nr_pages_per_call = nr_pages;
> -	gup.flags = write;
> +	if (write)
> +		gup.flags |= FOLL_WRITE;
>  
>  	fd = open("/sys/kernel/debug/gup_benchmark", O_RDWR);
>  	if (fd == -1)
> -- 
> 2.24.0
> 

Re: [PATCH v4 21/23] mm/gup_benchmark: support pin_user_pages() and related calls

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:27:08PM -0800, John Hubbard wrote:
> Up until now, gup_benchmark supported testing of the
> following kernel functions:
> 
> * get_user_pages(): via the '-U' command line option
> * get_user_pages_longterm(): via the '-L' command line option
> * get_user_pages_fast(): as the default (no options required)
> 
> Add test coverage for the new corresponding pin_*() functions:
> 
> * pin_user_pages(): via the '-c' command line option
> * pin_longterm_pages(): via the '-b' command line option
> * pin_user_pages_fast(): via the '-a' command line option
> 
> Also, add an option for clarity: '-u' for what is now (still) the
> default choice: get_user_pages_fast().
> 
> Also, for the three commands that set FOLL_PIN, verify that the pages
> really are dma-pinned, via the new is_dma_pinned() routine.
> Those commands are:
> 
>     PIN_FAST_BENCHMARK     : calls pin_user_pages_fast()
>     PIN_LONGTERM_BENCHMARK : calls pin_longterm_pages()
>     PIN_BENCHMARK          : calls pin_user_pages()
> 
> In between the calls to pin_*() and put_user_pages(),
> check each page: if page_dma_pinned() returns false, then
> WARN and return.
> 
> Do this outside of the benchmark timestamps, so that it doesn't
> affect reported times.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
>  mm/gup_benchmark.c                         | 73 ++++++++++++++++++++--
>  tools/testing/selftests/vm/gup_benchmark.c | 23 ++++++-
>  2 files changed, 90 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 7fc44d25eca7..8f980d91dbf5 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -8,6 +8,9 @@
>  #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
>  #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
> +#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
> +#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
> +#define PIN_BENCHMARK		_IOWR('g', 6, struct gup_benchmark)
>  
>  struct gup_benchmark {
>  	__u64 get_delta_usec;
> @@ -19,6 +22,44 @@ struct gup_benchmark {
>  	__u64 expansion[10];	/* For future use */
>  };
>  
> +static void put_back_pages(int cmd, struct page **pages, unsigned long nr_pages)
> +{
> +	int i;
> +
> +	switch (cmd) {
> +	case GUP_FAST_BENCHMARK:
> +	case GUP_LONGTERM_BENCHMARK:
> +	case GUP_BENCHMARK:
> +		for (i = 0; i < nr_pages; i++)
> +			put_page(pages[i]);
> +		break;
> +
> +	case PIN_FAST_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
> +	case PIN_BENCHMARK:
> +		put_user_pages(pages, nr_pages);
> +		break;
> +	}
> +}
> +
> +static void verify_dma_pinned(int cmd, struct page **pages,
> +			      unsigned long nr_pages)
> +{
> +	int i;
> +
> +	switch (cmd) {
> +	case PIN_FAST_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
> +	case PIN_BENCHMARK:
> +		for (i = 0; i < nr_pages; i++) {
> +			if (WARN(!page_dma_pinned(pages[i]),
> +				 "pages[%d] is NOT dma-pinned\n", i))
> +				break;
> +		}
> +		break;
> +	}
> +}
> +
>  static int __gup_benchmark_ioctl(unsigned int cmd,
>  		struct gup_benchmark *gup)
>  {
> @@ -65,6 +106,18 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  			nr = get_user_pages(addr, nr, gup->flags, pages + i,
>  					    NULL);
>  			break;
> +		case PIN_FAST_BENCHMARK:
> +			nr = pin_user_pages_fast(addr, nr, gup->flags,
> +						 pages + i);
> +			break;
> +		case PIN_LONGTERM_BENCHMARK:
> +			nr = pin_longterm_pages(addr, nr, gup->flags, pages + i,
> +						NULL);
> +			break;
> +		case PIN_BENCHMARK:
> +			nr = pin_user_pages(addr, nr, gup->flags, pages + i,
> +					    NULL);
> +			break;
>  		default:
>  			return -1;
>  		}
> @@ -75,15 +128,22 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  	}
>  	end_time = ktime_get();
>  
> +	/* Shifting the meaning of nr_pages: now it is actual number pinned: */
> +	nr_pages = i;
> +
>  	gup->get_delta_usec = ktime_us_delta(end_time, start_time);
>  	gup->size = addr - gup->addr;
>  
> +	/*
> +	 * Take an un-benchmark-timed moment to verify DMA pinned
> +	 * state: print a warning if any non-dma-pinned pages are found:
> +	 */
> +	verify_dma_pinned(cmd, pages, nr_pages);
> +
>  	start_time = ktime_get();
> -	for (i = 0; i < nr_pages; i++) {
> -		if (!pages[i])
> -			break;
> -		put_page(pages[i]);
> -	}
> +
> +	put_back_pages(cmd, pages, nr_pages);
> +
>  	end_time = ktime_get();
>  	gup->put_delta_usec = ktime_us_delta(end_time, start_time);
>  
> @@ -101,6 +161,9 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
>  	case GUP_FAST_BENCHMARK:
>  	case GUP_LONGTERM_BENCHMARK:
>  	case GUP_BENCHMARK:
> +	case PIN_FAST_BENCHMARK:
> +	case PIN_LONGTERM_BENCHMARK:
> +	case PIN_BENCHMARK:
>  		break;
>  	default:
>  		return -EINVAL;
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 389327e9b30a..03928e47a86f 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -18,6 +18,15 @@
>  #define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
>  
> +/*
> + * Similar to above, but use FOLL_PIN instead of FOLL_GET. This is done
> + * by calling pin_user_pages_fast(), pin_longterm_pages(), and pin_user_pages(),
> + * respectively.
> + */
> +#define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
> +#define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
> +#define PIN_BENCHMARK		_IOWR('g', 6, struct gup_benchmark)
> +
>  /* Just the flags we need, copied from mm.h: */
>  #define FOLL_WRITE	0x01	/* check pte is writable */
>  
> @@ -40,8 +49,17 @@ int main(int argc, char **argv)
>  	char *file = "/dev/zero";
>  	char *p;
>  
> -	while ((opt = getopt(argc, argv, "m:r:n:f:tTLUwSH")) != -1) {
> +	while ((opt = getopt(argc, argv, "m:r:n:f:abctTLUuwSH")) != -1) {
>  		switch (opt) {
> +		case 'a':
> +			cmd = PIN_FAST_BENCHMARK;
> +			break;
> +		case 'b':
> +			cmd = PIN_LONGTERM_BENCHMARK;
> +			break;
> +		case 'c':
> +			cmd = PIN_BENCHMARK;
> +			break;
>  		case 'm':
>  			size = atoi(optarg) * MB;
>  			break;
> @@ -63,6 +81,9 @@ int main(int argc, char **argv)
>  		case 'U':
>  			cmd = GUP_BENCHMARK;
>  			break;
> +		case 'u':
> +			cmd = GUP_FAST_BENCHMARK;
> +			break;
>  		case 'w':
>  			write = 1;
>  			break;
> -- 
> 2.24.0
> 

Re: [PATCH v4 22/23] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:27:09PM -0800, John Hubbard wrote:
> It's good to have basic unit test coverage of the new FOLL_PIN
> behavior. Fortunately, the gup_benchmark unit test is extremely
> fast (a few milliseconds), so adding it the the run_vmtests suite
> is going to cause no noticeable change in running time.
> 
> So, add two new invocations to run_vmtests:
> 
> 1) Run gup_benchmark with normal get_user_pages().
> 
> 2) Run gup_benchmark with pin_user_pages(). This is much like
> the first call, except that it sets FOLL_PIN.
> 
> Running these two in quick succession also provide a visual
> comparison of the running times, which is convenient.
> 
> The new invocations are fairly early in the run_vmtests script,
> because with test suites, it's usually preferable to put the
> shorter, faster tests first, all other things being equal.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
>  tools/testing/selftests/vm/run_vmtests | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests
> index 951c507a27f7..93e8dc9a7cad 100755
> --- a/tools/testing/selftests/vm/run_vmtests
> +++ b/tools/testing/selftests/vm/run_vmtests
> @@ -104,6 +104,28 @@ echo "NOTE: The above hugetlb tests provide minimal coverage.  Use"
>  echo "      https://github.com/libhugetlbfs/libhugetlbfs.git for"
>  echo "      hugetlb regression testing."
>  
> +echo "--------------------------------------------"
> +echo "running 'gup_benchmark -U' (normal/slow gup)"
> +echo "--------------------------------------------"
> +./gup_benchmark -U
> +if [ $? -ne 0 ]; then
> +	echo "[FAIL]"
> +	exitcode=1
> +else
> +	echo "[PASS]"
> +fi
> +
> +echo "------------------------------------------"
> +echo "running gup_benchmark -c (pin_user_pages)"
> +echo "------------------------------------------"
> +./gup_benchmark -c
> +if [ $? -ne 0 ]; then
> +	echo "[FAIL]"
> +	exitcode=1
> +else
> +	echo "[PASS]"
> +fi
> +
>  echo "-------------------"
>  echo "running userfaultfd"
>  echo "-------------------"
> -- 
> 2.24.0
> 

Re: [PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM)

[Ira Weiny]

On Tue, Nov 12, 2019 at 08:27:10PM -0800, John Hubbard wrote:
> Now that all other kernel callers of get_user_pages(FOLL_LONGTERM)
> have been converted to pin_longterm_pages(), lock it down:
> 
> 1) Add an assertion to get_user_pages(), preventing callers from
>    passing FOLL_LONGTERM (in addition to the existing assertion that
>    prevents FOLL_PIN).
> 
> 2) Remove the associated GUP_LONGTERM_BENCHMARK test.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  mm/gup.c                                   | 8 ++++----
>  mm/gup_benchmark.c                         | 9 +--------
>  tools/testing/selftests/vm/gup_benchmark.c | 7 ++-----
>  3 files changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 82e7e4ce5027..90f5f95ee7ac 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1756,11 +1756,11 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>  		struct vm_area_struct **vmas)
>  {
>  	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_page*() and
> -	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
> -	 * with an assertion:
> +	 * FOLL_PIN and FOLL_LONGTERM must only be set internally by the
> +	 * pin_user_page*() and pin_longterm_*() APIs, never directly by the
> +	 * caller, so enforce that with an assertion:
>  	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_LONGTERM)))

Don't we want to block FOLL_LONGTERM in get_user_pages_fast() as well after all
this?

Ira

>  		return -EINVAL;
>  
>  	return __gup_longterm_locked(current, current->mm, start, nr_pages,
> diff --git a/mm/gup_benchmark.c b/mm/gup_benchmark.c
> index 8f980d91dbf5..679f0e6a0adb 100644
> --- a/mm/gup_benchmark.c
> +++ b/mm/gup_benchmark.c
> @@ -6,7 +6,7 @@
>  #include <linux/debugfs.h>
>  
>  #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
> -#define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
> +/* Command 2 has been deleted. */
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
>  #define PIN_FAST_BENCHMARK	_IOWR('g', 4, struct gup_benchmark)
>  #define PIN_LONGTERM_BENCHMARK	_IOWR('g', 5, struct gup_benchmark)
> @@ -28,7 +28,6 @@ static void put_back_pages(int cmd, struct page **pages, unsigned long nr_pages)
>  
>  	switch (cmd) {
>  	case GUP_FAST_BENCHMARK:
> -	case GUP_LONGTERM_BENCHMARK:
>  	case GUP_BENCHMARK:
>  		for (i = 0; i < nr_pages; i++)
>  			put_page(pages[i]);
> @@ -97,11 +96,6 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
>  			nr = get_user_pages_fast(addr, nr, gup->flags,
>  						 pages + i);
>  			break;
> -		case GUP_LONGTERM_BENCHMARK:
> -			nr = get_user_pages(addr, nr,
> -					    gup->flags | FOLL_LONGTERM,
> -					    pages + i, NULL);
> -			break;
>  		case GUP_BENCHMARK:
>  			nr = get_user_pages(addr, nr, gup->flags, pages + i,
>  					    NULL);
> @@ -159,7 +153,6 @@ static long gup_benchmark_ioctl(struct file *filep, unsigned int cmd,
>  
>  	switch (cmd) {
>  	case GUP_FAST_BENCHMARK:
> -	case GUP_LONGTERM_BENCHMARK:
>  	case GUP_BENCHMARK:
>  	case PIN_FAST_BENCHMARK:
>  	case PIN_LONGTERM_BENCHMARK:
> diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
> index 03928e47a86f..836b7082db13 100644
> --- a/tools/testing/selftests/vm/gup_benchmark.c
> +++ b/tools/testing/selftests/vm/gup_benchmark.c
> @@ -15,7 +15,7 @@
>  #define PAGE_SIZE sysconf(_SC_PAGESIZE)
>  
>  #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
> -#define GUP_LONGTERM_BENCHMARK	_IOWR('g', 2, struct gup_benchmark)
> +/* Command 2 has been deleted. */
>  #define GUP_BENCHMARK		_IOWR('g', 3, struct gup_benchmark)
>  
>  /*
> @@ -49,7 +49,7 @@ int main(int argc, char **argv)
>  	char *file = "/dev/zero";
>  	char *p;
>  
> -	while ((opt = getopt(argc, argv, "m:r:n:f:abctTLUuwSH")) != -1) {
> +	while ((opt = getopt(argc, argv, "m:r:n:f:abctTUuwSH")) != -1) {
>  		switch (opt) {
>  		case 'a':
>  			cmd = PIN_FAST_BENCHMARK;
> @@ -75,9 +75,6 @@ int main(int argc, char **argv)
>  		case 'T':
>  			thp = 0;
>  			break;
> -		case 'L':
> -			cmd = GUP_LONGTERM_BENCHMARK;
> -			break;
>  		case 'U':
>  			cmd = GUP_BENCHMARK;
>  			break;
> -- 
> 2.24.0
> 

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Jerome Glisse]

On Tue, Nov 12, 2019 at 08:26:51PM -0800, John Hubbard wrote:
> An upcoming patch changes and complicates the refcounting and
> especially the "put page" aspects of it. In order to keep
> everything clean, refactor the devmap page release routines:
> 
> * Rename put_devmap_managed_page() to page_is_devmap_managed(),
>   and limit the functionality to "read only": return a bool,
>   with no side effects.
> 
> * Add a new routine, put_devmap_managed_page(), to handle checking
>   what kind of page it is, and what kind of refcount handling it
>   requires.
> 
> * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
>   and limit the functionality to unconditionally freeing a devmap
>   page.
> 
> This is originally based on a separate patch by Ira Weiny, which
> applied to an early version of the put_user_page() experiments.
> Since then, Jérôme Glisse suggested the refactoring described above.
> 
> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> ---
>  include/linux/mm.h | 27 ++++++++++++++++---
>  mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
>  2 files changed, 53 insertions(+), 41 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a2adf95b3f9c..96228376139c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
>  #endif
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page);
> +void free_devmap_managed_page(struct page *page);
>  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> -static inline bool put_devmap_managed_page(struct page *page)
> +
> +static inline bool page_is_devmap_managed(struct page *page)
>  {
>  	if (!static_branch_unlikely(&devmap_managed_key))
>  		return false;
> @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
>  	switch (page->pgmap->type) {
>  	case MEMORY_DEVICE_PRIVATE:
>  	case MEMORY_DEVICE_FS_DAX:
> -		__put_devmap_managed_page(page);
>  		return true;
>  	default:
>  		break;
> @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
>  	return false;
>  }
>  
> +static inline bool put_devmap_managed_page(struct page *page)
> +{
> +	bool is_devmap = page_is_devmap_managed(page);
> +
> +	if (is_devmap) {
> +		int count = page_ref_dec_return(page);
> +
> +		/*
> +		 * devmap page refcounts are 1-based, rather than 0-based: if
> +		 * refcount is 1, then the page is free and the refcount is
> +		 * stable because nobody holds a reference on the page.
> +		 */
> +		if (count == 1)
> +			free_devmap_managed_page(page);
> +		else if (!count)
> +			__put_page(page);
> +	}
> +
> +	return is_devmap;
> +}
> +
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
>  static inline bool put_devmap_managed_page(struct page *page)
>  {
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..bc7e2a27d025 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  EXPORT_SYMBOL_GPL(get_dev_pagemap);
>  
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page)
> +void free_devmap_managed_page(struct page *page)
>  {
> -	int count = page_ref_dec_return(page);
> +	/* Clear Active bit in case of parallel mark_page_accessed */
> +	__ClearPageActive(page);
> +	__ClearPageWaiters(page);
> +
> +	mem_cgroup_uncharge(page);
>  
>  	/*
> -	 * If refcount is 1 then page is freed and refcount is stable as nobody
> -	 * holds a reference on the page.
> +	 * When a device_private page is freed, the page->mapping field
> +	 * may still contain a (stale) mapping value. For example, the
> +	 * lower bits of page->mapping may still identify the page as
> +	 * an anonymous page. Ultimately, this entire field is just
> +	 * stale and wrong, and it will cause errors if not cleared.
> +	 * One example is:
> +	 *
> +	 *  migrate_vma_pages()
> +	 *    migrate_vma_insert_page()
> +	 *      page_add_new_anon_rmap()
> +	 *        __page_set_anon_rmap()
> +	 *          ...checks page->mapping, via PageAnon(page) call,
> +	 *            and incorrectly concludes that the page is an
> +	 *            anonymous page. Therefore, it incorrectly,
> +	 *            silently fails to set up the new anon rmap.
> +	 *
> +	 * For other types of ZONE_DEVICE pages, migration is either
> +	 * handled differently or not done at all, so there is no need
> +	 * to clear page->mapping.
>  	 */
> -	if (count == 1) {
> -		/* Clear Active bit in case of parallel mark_page_accessed */
> -		__ClearPageActive(page);
> -		__ClearPageWaiters(page);
> -
> -		mem_cgroup_uncharge(page);
> -
> -		/*
> -		 * When a device_private page is freed, the page->mapping field
> -		 * may still contain a (stale) mapping value. For example, the
> -		 * lower bits of page->mapping may still identify the page as
> -		 * an anonymous page. Ultimately, this entire field is just
> -		 * stale and wrong, and it will cause errors if not cleared.
> -		 * One example is:
> -		 *
> -		 *  migrate_vma_pages()
> -		 *    migrate_vma_insert_page()
> -		 *      page_add_new_anon_rmap()
> -		 *        __page_set_anon_rmap()
> -		 *          ...checks page->mapping, via PageAnon(page) call,
> -		 *            and incorrectly concludes that the page is an
> -		 *            anonymous page. Therefore, it incorrectly,
> -		 *            silently fails to set up the new anon rmap.
> -		 *
> -		 * For other types of ZONE_DEVICE pages, migration is either
> -		 * handled differently or not done at all, so there is no need
> -		 * to clear page->mapping.
> -		 */
> -		if (is_device_private_page(page))
> -			page->mapping = NULL;
> +	if (is_device_private_page(page))
> +		page->mapping = NULL;
>  
> -		page->pgmap->ops->page_free(page);
> -	} else if (!count)
> -		__put_page(page);
> +	page->pgmap->ops->page_free(page);
>  }
> -EXPORT_SYMBOL(__put_devmap_managed_page);
> +EXPORT_SYMBOL(free_devmap_managed_page);
>  #endif /* CONFIG_DEV_PAGEMAP_OPS */
> -- 
> 2.24.0
> 

Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

[Ira Weiny]

On Wed, Nov 13, 2019 at 09:02:02AM -0400, Jason Gunthorpe wrote:
> On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote:
> > As it says in the updated comment in gup.c: current FOLL_LONGTERM
> > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the
> > FS DAX check requirement on vmas.
> > 
> > However, the corresponding restriction in get_user_pages_remote() was
> > slightly stricter than is actually required: it forbade all
> > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
> > that do not set the "locked" arg.
> > 
> > Update the code and comments accordingly, and update the VFIO caller
> > to take advantage of this, fixing a bug as a result: the VFIO caller
> > is logically a FOLL_LONGTERM user.
> > 
> > Also, remove an unnessary pair of calls that were releasing and
> > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem
> > just in order to call page_to_pfn().
> > 
> > Also, move the DAX check ("if a VMA is DAX, don't allow long term
> > pinning") from the VFIO call site, all the way into the internals
> > of get_user_pages_remote() and __gup_longterm_locked(). That is:
> > get_user_pages_remote() calls __gup_longterm_locked(), which in turn
> > calls check_dax_vmas(). It's lightly explained in the comments as well.
> > 
> > Thanks to Jason Gunthorpe for pointing out a clean way to fix this,
> > and to Dan Williams for helping clarify the DAX refactoring.
> > 
> > Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Jerome Glisse <jglisse@redhat.com>
> > Cc: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> >  drivers/vfio/vfio_iommu_type1.c | 25 ++-----------------------
> >  mm/gup.c                        | 27 ++++++++++++++++++++++-----
> >  2 files changed, 24 insertions(+), 28 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index d864277ea16f..7301b710c9a4 100644
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> >  {
> >  	struct page *page[1];
> >  	struct vm_area_struct *vma;
> > -	struct vm_area_struct *vmas[1];
> >  	unsigned int flags = 0;
> >  	int ret;
> >  
> > @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> >  		flags |= FOLL_WRITE;
> >  
> >  	down_read(&mm->mmap_sem);
> > -	if (mm == current->mm) {
> > -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
> > -				     vmas);
> > -	} else {
> > -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
> > -					    vmas, NULL);
> > -		/*
> > -		 * The lifetime of a vaddr_get_pfn() page pin is
> > -		 * userspace-controlled. In the fs-dax case this could
> > -		 * lead to indefinite stalls in filesystem operations.
> > -		 * Disallow attempts to pin fs-dax pages via this
> > -		 * interface.
> > -		 */
> > -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
> > -			ret = -EOPNOTSUPP;
> > -			put_page(page[0]);
> > -		}
> > -	}
> > -	up_read(&mm->mmap_sem);
> > -
> > +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
> > +				    page, NULL, NULL);
> >  	if (ret == 1) {
> >  		*pfn = page_to_pfn(page[0]);
> >  		return 0;
> 
> Mind the return with the lock held this needs some goto unwind

Ah yea...  retract my reviewed by...  :-(

Ira

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Dan Williams]

On Tue, Nov 12, 2019 at 8:27 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> An upcoming patch changes and complicates the refcounting and
> especially the "put page" aspects of it. In order to keep
> everything clean, refactor the devmap page release routines:
>
> * Rename put_devmap_managed_page() to page_is_devmap_managed(),
>   and limit the functionality to "read only": return a bool,
>   with no side effects.
>
> * Add a new routine, put_devmap_managed_page(), to handle checking
>   what kind of page it is, and what kind of refcount handling it
>   requires.
>
> * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
>   and limit the functionality to unconditionally freeing a devmap
>   page.
>
> This is originally based on a separate patch by Ira Weiny, which
> applied to an early version of the put_user_page() experiments.
> Since then, Jérôme Glisse suggested the refactoring described above.
>
> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h | 27 ++++++++++++++++---
>  mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
>  2 files changed, 53 insertions(+), 41 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a2adf95b3f9c..96228376139c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
>  #endif
>
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page);
> +void free_devmap_managed_page(struct page *page);
>  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> -static inline bool put_devmap_managed_page(struct page *page)
> +
> +static inline bool page_is_devmap_managed(struct page *page)
>  {
>         if (!static_branch_unlikely(&devmap_managed_key))
>                 return false;
> @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
>         switch (page->pgmap->type) {
>         case MEMORY_DEVICE_PRIVATE:
>         case MEMORY_DEVICE_FS_DAX:
> -               __put_devmap_managed_page(page);
>                 return true;
>         default:
>                 break;
> @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
>         return false;
>  }
>
> +static inline bool put_devmap_managed_page(struct page *page)
> +{
> +       bool is_devmap = page_is_devmap_managed(page);
> +
> +       if (is_devmap) {
> +               int count = page_ref_dec_return(page);
> +
> +               /*
> +                * devmap page refcounts are 1-based, rather than 0-based: if
> +                * refcount is 1, then the page is free and the refcount is
> +                * stable because nobody holds a reference on the page.
> +                */
> +               if (count == 1)
> +                       free_devmap_managed_page(page);
> +               else if (!count)
> +                       __put_page(page);
> +       }
> +
> +       return is_devmap;
> +}
> +
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
>  static inline bool put_devmap_managed_page(struct page *page)
>  {
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..bc7e2a27d025 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
>  EXPORT_SYMBOL_GPL(get_dev_pagemap);
>
>  #ifdef CONFIG_DEV_PAGEMAP_OPS
> -void __put_devmap_managed_page(struct page *page)
> +void free_devmap_managed_page(struct page *page)
>  {
> -       int count = page_ref_dec_return(page);
> +       /* Clear Active bit in case of parallel mark_page_accessed */
> +       __ClearPageActive(page);
> +       __ClearPageWaiters(page);
> +
> +       mem_cgroup_uncharge(page);

Ugh, when did all this HMM specific manipulation sneak into the
generic ZONE_DEVICE path? It used to be gated by pgmap type with its
own put_zone_device_private_page(). For example it's certainly
unnecessary and might be broken (would need to check) to call
mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
monolith and the HMM use case leaks pages into code paths that DAX
explicitly avoids.

Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

[John Hubbard]

On 11/13/19 11:17 AM, Ira Weiny wrote:
...
>>> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>>>   		flags |= FOLL_WRITE;
>>>   
>>>   	down_read(&mm->mmap_sem);
>>> -	if (mm == current->mm) {
>>> -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
>>> -				     vmas);
>>> -	} else {
>>> -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
>>> -					    vmas, NULL);
>>> -		/*
>>> -		 * The lifetime of a vaddr_get_pfn() page pin is
>>> -		 * userspace-controlled. In the fs-dax case this could
>>> -		 * lead to indefinite stalls in filesystem operations.
>>> -		 * Disallow attempts to pin fs-dax pages via this
>>> -		 * interface.
>>> -		 */
>>> -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
>>> -			ret = -EOPNOTSUPP;
>>> -			put_page(page[0]);
>>> -		}
>>> -	}
>>> -	up_read(&mm->mmap_sem);
>>> -
>>> +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
>>> +				    page, NULL, NULL);
>>>   	if (ret == 1) {
>>>   		*pfn = page_to_pfn(page[0]);
>>>   		return 0;
>>
>> Mind the return with the lock held this needs some goto unwind
> 
> Ah yea...  retract my reviewed by...  :-(
> 

ooops, embarrassed that I missed that, good catch. Will repost with it fixed.



thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[John Hubbard]

On 11/13/19 10:59 AM, Ira Weiny wrote:
> On Tue, Nov 12, 2019 at 08:26:56PM -0800, John Hubbard wrote:
>> Introduce pin_user_pages*() variations of get_user_pages*() calls,
>> and also pin_longterm_pages*() variations.
>>
>> These variants all set FOLL_PIN, which is also introduced, and
>> thoroughly documented.
>>
>> The pin_longterm*() variants also set FOLL_LONGTERM, in addition
>> to FOLL_PIN:
>>
>>      pin_user_pages()
>>      pin_user_pages_remote()
>>      pin_user_pages_fast()
>>
>>      pin_longterm_pages()
>>      pin_longterm_pages_remote()
>>      pin_longterm_pages_fast()
> 
> At some point in this conversation I thought we were going to put in "unpin_*"
> versions of these.
> 
> Is that still in the plans?
> 

Why yes it is! :)  Daniel Vetter and Jan Kara both already weighed in [1],
in favor of "unpin_user_page*()", rather than "put_user_page*()".

I'll change those names.

[1] https://lore.kernel.org/r/20191113101210.GD6367@quack2.suse.cz


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Dan Williams]

On Wed, Nov 13, 2019 at 11:23 AM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Tue, Nov 12, 2019 at 8:27 PM John Hubbard <jhubbard@nvidia.com> wrote:
> >
> > An upcoming patch changes and complicates the refcounting and
> > especially the "put page" aspects of it. In order to keep
> > everything clean, refactor the devmap page release routines:
> >
> > * Rename put_devmap_managed_page() to page_is_devmap_managed(),
> >   and limit the functionality to "read only": return a bool,
> >   with no side effects.
> >
> > * Add a new routine, put_devmap_managed_page(), to handle checking
> >   what kind of page it is, and what kind of refcount handling it
> >   requires.
> >
> > * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
> >   and limit the functionality to unconditionally freeing a devmap
> >   page.
> >
> > This is originally based on a separate patch by Ira Weiny, which
> > applied to an early version of the put_user_page() experiments.
> > Since then, Jérôme Glisse suggested the refactoring described above.
> >
> > Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> > ---
> >  include/linux/mm.h | 27 ++++++++++++++++---
> >  mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
> >  2 files changed, 53 insertions(+), 41 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index a2adf95b3f9c..96228376139c 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
> >  #endif
> >
> >  #ifdef CONFIG_DEV_PAGEMAP_OPS
> > -void __put_devmap_managed_page(struct page *page);
> > +void free_devmap_managed_page(struct page *page);
> >  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> > -static inline bool put_devmap_managed_page(struct page *page)
> > +
> > +static inline bool page_is_devmap_managed(struct page *page)
> >  {
> >         if (!static_branch_unlikely(&devmap_managed_key))
> >                 return false;
> > @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
> >         switch (page->pgmap->type) {
> >         case MEMORY_DEVICE_PRIVATE:
> >         case MEMORY_DEVICE_FS_DAX:
> > -               __put_devmap_managed_page(page);
> >                 return true;
> >         default:
> >                 break;
> > @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
> >         return false;
> >  }
> >
> > +static inline bool put_devmap_managed_page(struct page *page)
> > +{
> > +       bool is_devmap = page_is_devmap_managed(page);
> > +
> > +       if (is_devmap) {
> > +               int count = page_ref_dec_return(page);
> > +
> > +               /*
> > +                * devmap page refcounts are 1-based, rather than 0-based: if
> > +                * refcount is 1, then the page is free and the refcount is
> > +                * stable because nobody holds a reference on the page.
> > +                */
> > +               if (count == 1)
> > +                       free_devmap_managed_page(page);
> > +               else if (!count)
> > +                       __put_page(page);
> > +       }
> > +
> > +       return is_devmap;
> > +}
> > +
> >  #else /* CONFIG_DEV_PAGEMAP_OPS */
> >  static inline bool put_devmap_managed_page(struct page *page)
> >  {
> > diff --git a/mm/memremap.c b/mm/memremap.c
> > index 03ccbdfeb697..bc7e2a27d025 100644
> > --- a/mm/memremap.c
> > +++ b/mm/memremap.c
> > @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> >  EXPORT_SYMBOL_GPL(get_dev_pagemap);
> >
> >  #ifdef CONFIG_DEV_PAGEMAP_OPS
> > -void __put_devmap_managed_page(struct page *page)
> > +void free_devmap_managed_page(struct page *page)
> >  {
> > -       int count = page_ref_dec_return(page);
> > +       /* Clear Active bit in case of parallel mark_page_accessed */
> > +       __ClearPageActive(page);
> > +       __ClearPageWaiters(page);
> > +
> > +       mem_cgroup_uncharge(page);
>
> Ugh, when did all this HMM specific manipulation sneak into the
> generic ZONE_DEVICE path? It used to be gated by pgmap type with its
> own put_zone_device_private_page(). For example it's certainly
> unnecessary and might be broken (would need to check) to call
> mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
> monolith and the HMM use case leaks pages into code paths that DAX
> explicitly avoids.

It's been this way for a while and I did not react previously,
apologies for that. I think __ClearPageActive, __ClearPageWaiters, and
mem_cgroup_uncharge, belong behind a device-private conditional. The
history here is:

Move some, but not all HMM specifics to hmm_devmem_free():
    2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put

Remove the clearing of mapping since no upstream consumers needed it:
    b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free

Add it back in once an upstream consumer arrived:
    7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse

We're now almost entirely free of ->page_free callbacks except for
that weird nouveau case, can that FIXME in nouveau_dmem_page_free()
also result in killing the ->page_free() callback altogether? In the
meantime I'm proposing a cleanup like this:

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index ad8e4df1282b..4eae441f86c9 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem)
        put_disk(pmem->disk);
 }

-static void pmem_pagemap_page_free(struct page *page)
-{
-       wake_up_var(&page->_refcount);
-}
-
 static const struct dev_pagemap_ops fsdax_pagemap_ops = {
-       .page_free              = pmem_pagemap_page_free,
        .kill                   = pmem_pagemap_kill,
        .cleanup                = pmem_pagemap_cleanup,
 };
diff --git a/mm/memremap.c b/mm/memremap.c
index 03ccbdfeb697..157edb8f7cf8 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
         * holds a reference on the page.
         */
        if (count == 1) {
-               /* Clear Active bit in case of parallel mark_page_accessed */
-               __ClearPageActive(page);
-               __ClearPageWaiters(page);
-
-               mem_cgroup_uncharge(page);
-
                /*
                 * When a device_private page is freed, the page->mapping field
                 * may still contain a (stale) mapping value. For example, the
@@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
                 * handled differently or not done at all, so there is no need
                 * to clear page->mapping.
                 */
-               if (is_device_private_page(page))
-                       page->mapping = NULL;
+               if (is_device_private_page(page)) {
+                       /* Clear Active bit in case of parallel
mark_page_accessed */
+                       __ClearPageActive(page);
+                       __ClearPageWaiters(page);

-               page->pgmap->ops->page_free(page);
+                       mem_cgroup_uncharge(page);
+
+                       page->mapping = NULL;
+                       page->pgmap->ops->page_free(page);
+               } else
+                       wake_up_var(&page->_refcount);
        } else if (!count)
                __put_page(page);
 }

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[John Hubbard]

On 11/13/19 2:00 PM, Dan Williams wrote:
...
>> Ugh, when did all this HMM specific manipulation sneak into the
>> generic ZONE_DEVICE path? It used to be gated by pgmap type with its
>> own put_zone_device_private_page(). For example it's certainly
>> unnecessary and might be broken (would need to check) to call
>> mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
>> monolith and the HMM use case leaks pages into code paths that DAX
>> explicitly avoids.
> 
> It's been this way for a while and I did not react previously,
> apologies for that. I think __ClearPageActive, __ClearPageWaiters, and
> mem_cgroup_uncharge, belong behind a device-private conditional. The
> history here is:
> 
> Move some, but not all HMM specifics to hmm_devmem_free():
>      2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put
> 
> Remove the clearing of mapping since no upstream consumers needed it:
>      b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free
> 
> Add it back in once an upstream consumer arrived:
>      7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse
> 
> We're now almost entirely free of ->page_free callbacks except for
> that weird nouveau case, can that FIXME in nouveau_dmem_page_free()
> also result in killing the ->page_free() callback altogether? In the
> meantime I'm proposing a cleanup like this:


OK, assuming this is acceptable (no obvious problems jump out at me,
and we can also test it with HMM), then how would you like to proceed, as
far as patches go: add such a patch as part of this series here, or as a
stand-alone patch either before or after this series? Or something else?
And did you plan on sending it out as such?

Also, the diffs didn't quite make it through intact to my "git apply", so
I'm re-posting the diff in hopes that this time it survives:

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index f9f76f6ba07b..21db1ce8c0ae 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
  	put_disk(pmem->disk);
  }
  
-static void pmem_pagemap_page_free(struct page *page)
-{
-	wake_up_var(&page->_refcount);
-}
-
  static const struct dev_pagemap_ops fsdax_pagemap_ops = {
-	.page_free		= pmem_pagemap_page_free,
  	.kill			= pmem_pagemap_kill,
  	.cleanup		= pmem_pagemap_cleanup,
  };
diff --git a/mm/memremap.c b/mm/memremap.c
index 03ccbdfeb697..157edb8f7cf8 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
  	 * holds a reference on the page.
  	 */
  	if (count == 1) {
-		/* Clear Active bit in case of parallel mark_page_accessed */
-		__ClearPageActive(page);
-		__ClearPageWaiters(page);
-
-		mem_cgroup_uncharge(page);
-
  		/*
  		 * When a device_private page is freed, the page->mapping field
  		 * may still contain a (stale) mapping value. For example, the
@@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
  		 * handled differently or not done at all, so there is no need
  		 * to clear page->mapping.
  		 */
-		if (is_device_private_page(page))
-			page->mapping = NULL;
+		if (is_device_private_page(page)) {
+			/* Clear Active bit in case of parallel mark_page_accessed */
+			__ClearPageActive(page);
+			__ClearPageWaiters(page);
  
-		page->pgmap->ops->page_free(page);
+			mem_cgroup_uncharge(page);
+
+			page->mapping = NULL;
+			page->pgmap->ops->page_free(page);
+		} else
+			wake_up_var(&page->_refcount);
  	} else if (!count)
  		__put_page(page);
  }
-- 
2.24.0


thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index ad8e4df1282b..4eae441f86c9 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem)
>          put_disk(pmem->disk);
>   }
> 
> -static void pmem_pagemap_page_free(struct page *page)
> -{
> -       wake_up_var(&page->_refcount);
> -}
> -
>   static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> -       .page_free              = pmem_pagemap_page_free,
>          .kill                   = pmem_pagemap_kill,
>          .cleanup                = pmem_pagemap_cleanup,
>   };
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..157edb8f7cf8 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
>           * holds a reference on the page.
>           */
>          if (count == 1) {
> -               /* Clear Active bit in case of parallel mark_page_accessed */
> -               __ClearPageActive(page);
> -               __ClearPageWaiters(page);
> -
> -               mem_cgroup_uncharge(page);
> -
>                  /*
>                   * When a device_private page is freed, the page->mapping field
>                   * may still contain a (stale) mapping value. For example, the
> @@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
>                   * handled differently or not done at all, so there is no need
>                   * to clear page->mapping.
>                   */
> -               if (is_device_private_page(page))
> -                       page->mapping = NULL;
> +               if (is_device_private_page(page)) {
> +                       /* Clear Active bit in case of parallel
> mark_page_accessed */
> +                       __ClearPageActive(page);
> +                       __ClearPageWaiters(page);
> 
> -               page->pgmap->ops->page_free(page);
> +                       mem_cgroup_uncharge(page);
> +
> +                       page->mapping = NULL;
> +                       page->pgmap->ops->page_free(page);
> +               } else
> +                       wake_up_var(&page->_refcount);
>          } else if (!count)
>                  __put_page(page);
>   }
> 

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Dan Williams]

On Wed, Nov 13, 2019 at 2:49 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 11/13/19 2:00 PM, Dan Williams wrote:
> ...
> >> Ugh, when did all this HMM specific manipulation sneak into the
> >> generic ZONE_DEVICE path? It used to be gated by pgmap type with its
> >> own put_zone_device_private_page(). For example it's certainly
> >> unnecessary and might be broken (would need to check) to call
> >> mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
> >> monolith and the HMM use case leaks pages into code paths that DAX
> >> explicitly avoids.
> >
> > It's been this way for a while and I did not react previously,
> > apologies for that. I think __ClearPageActive, __ClearPageWaiters, and
> > mem_cgroup_uncharge, belong behind a device-private conditional. The
> > history here is:
> >
> > Move some, but not all HMM specifics to hmm_devmem_free():
> >      2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put
> >
> > Remove the clearing of mapping since no upstream consumers needed it:
> >      b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free
> >
> > Add it back in once an upstream consumer arrived:
> >      7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse
> >
> > We're now almost entirely free of ->page_free callbacks except for
> > that weird nouveau case, can that FIXME in nouveau_dmem_page_free()
> > also result in killing the ->page_free() callback altogether? In the
> > meantime I'm proposing a cleanup like this:
>
>
> OK, assuming this is acceptable (no obvious problems jump out at me,
> and we can also test it with HMM), then how would you like to proceed, as
> far as patches go: add such a patch as part of this series here, or as a
> stand-alone patch either before or after this series? Or something else?
> And did you plan on sending it out as such?

I think it makes sense to include it in your series since you're
looking to refactor the implementation. I can send you one based on
current linux-next as a lead-in cleanup before the refactor. Does that
work for you?

>
> Also, the diffs didn't quite make it through intact to my "git apply", so
> I'm re-posting the diff in hopes that this time it survives:

Apologies for that. For quick "how about this" patch examples, I just
copy and paste into gmail and it sometimes clobbers it.

>
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index f9f76f6ba07b..21db1ce8c0ae 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
>         put_disk(pmem->disk);
>   }
>
> -static void pmem_pagemap_page_free(struct page *page)
> -{
> -       wake_up_var(&page->_refcount);
> -}
> -
>   static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> -       .page_free              = pmem_pagemap_page_free,
>         .kill                   = pmem_pagemap_kill,
>         .cleanup                = pmem_pagemap_cleanup,
>   };
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..157edb8f7cf8 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
>          * holds a reference on the page.
>          */
>         if (count == 1) {
> -               /* Clear Active bit in case of parallel mark_page_accessed */
> -               __ClearPageActive(page);
> -               __ClearPageWaiters(page);
> -
> -               mem_cgroup_uncharge(page);
> -
>                 /*
>                  * When a device_private page is freed, the page->mapping field
>                  * may still contain a (stale) mapping value. For example, the
> @@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
>                  * handled differently or not done at all, so there is no need
>                  * to clear page->mapping.
>                  */
> -               if (is_device_private_page(page))
> -                       page->mapping = NULL;
> +               if (is_device_private_page(page)) {
> +                       /* Clear Active bit in case of parallel mark_page_accessed */
> +                       __ClearPageActive(page);
> +                       __ClearPageWaiters(page);
>
> -               page->pgmap->ops->page_free(page);
> +                       mem_cgroup_uncharge(page);
> +
> +                       page->mapping = NULL;
> +                       page->pgmap->ops->page_free(page);
> +               } else
> +                       wake_up_var(&page->_refcount);
>         } else if (!count)
>                 __put_page(page);
>   }
> --
> 2.24.0
>
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index ad8e4df1282b..4eae441f86c9 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem)
> >          put_disk(pmem->disk);
> >   }
> >
> > -static void pmem_pagemap_page_free(struct page *page)
> > -{
> > -       wake_up_var(&page->_refcount);
> > -}
> > -
> >   static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> > -       .page_free              = pmem_pagemap_page_free,
> >          .kill                   = pmem_pagemap_kill,
> >          .cleanup                = pmem_pagemap_cleanup,
> >   };
> > diff --git a/mm/memremap.c b/mm/memremap.c
> > index 03ccbdfeb697..157edb8f7cf8 100644
> > --- a/mm/memremap.c
> > +++ b/mm/memremap.c
> > @@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
> >           * holds a reference on the page.
> >           */
> >          if (count == 1) {
> > -               /* Clear Active bit in case of parallel mark_page_accessed */
> > -               __ClearPageActive(page);
> > -               __ClearPageWaiters(page);
> > -
> > -               mem_cgroup_uncharge(page);
> > -
> >                  /*
> >                   * When a device_private page is freed, the page->mapping field
> >                   * may still contain a (stale) mapping value. For example, the
> > @@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
> >                   * handled differently or not done at all, so there is no need
> >                   * to clear page->mapping.
> >                   */
> > -               if (is_device_private_page(page))
> > -                       page->mapping = NULL;
> > +               if (is_device_private_page(page)) {
> > +                       /* Clear Active bit in case of parallel
> > mark_page_accessed */
> > +                       __ClearPageActive(page);
> > +                       __ClearPageWaiters(page);
> >
> > -               page->pgmap->ops->page_free(page);
> > +                       mem_cgroup_uncharge(page);
> > +
> > +                       page->mapping = NULL;
> > +                       page->pgmap->ops->page_free(page);
> > +               } else
> > +                       wake_up_var(&page->_refcount);
> >          } else if (!count)
> >                  __put_page(page);
> >   }
> >

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[John Hubbard]

On 11/13/19 2:55 PM, Dan Williams wrote:
> On Wed, Nov 13, 2019 at 2:49 PM John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> On 11/13/19 2:00 PM, Dan Williams wrote:
>> ...
>>>> Ugh, when did all this HMM specific manipulation sneak into the
>>>> generic ZONE_DEVICE path? It used to be gated by pgmap type with its
>>>> own put_zone_device_private_page(). For example it's certainly
>>>> unnecessary and might be broken (would need to check) to call
>>>> mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
>>>> monolith and the HMM use case leaks pages into code paths that DAX
>>>> explicitly avoids.
>>>
>>> It's been this way for a while and I did not react previously,
>>> apologies for that. I think __ClearPageActive, __ClearPageWaiters, and
>>> mem_cgroup_uncharge, belong behind a device-private conditional. The
>>> history here is:
>>>
>>> Move some, but not all HMM specifics to hmm_devmem_free():
>>>       2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put
>>>
>>> Remove the clearing of mapping since no upstream consumers needed it:
>>>       b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free
>>>
>>> Add it back in once an upstream consumer arrived:
>>>       7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse
>>>
>>> We're now almost entirely free of ->page_free callbacks except for
>>> that weird nouveau case, can that FIXME in nouveau_dmem_page_free()
>>> also result in killing the ->page_free() callback altogether? In the
>>> meantime I'm proposing a cleanup like this:
>>
>>
>> OK, assuming this is acceptable (no obvious problems jump out at me,
>> and we can also test it with HMM), then how would you like to proceed, as
>> far as patches go: add such a patch as part of this series here, or as a
>> stand-alone patch either before or after this series? Or something else?
>> And did you plan on sending it out as such?
> 
> I think it makes sense to include it in your series since you're
> looking to refactor the implementation. I can send you one based on
> current linux-next as a lead-in cleanup before the refactor. Does that
> work for you?
> 

That would be perfect!

>>
>> Also, the diffs didn't quite make it through intact to my "git apply", so
>> I'm re-posting the diff in hopes that this time it survives:
> 
> Apologies for that. For quick "how about this" patch examples, I just
> copy and paste into gmail and it sometimes clobbers it.
> 

No problem at all, I do the same thing and *usually* it works. ha. And
as you say, it's good enough for discussions.


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[Jerome Glisse]

On Wed, Nov 13, 2019 at 02:00:06PM -0800, Dan Williams wrote:
> On Wed, Nov 13, 2019 at 11:23 AM Dan Williams <dan.j.williams@intel.com> wrote:
> >
> > On Tue, Nov 12, 2019 at 8:27 PM John Hubbard <jhubbard@nvidia.com> wrote:
> > >
> > > An upcoming patch changes and complicates the refcounting and
> > > especially the "put page" aspects of it. In order to keep
> > > everything clean, refactor the devmap page release routines:
> > >
> > > * Rename put_devmap_managed_page() to page_is_devmap_managed(),
> > >   and limit the functionality to "read only": return a bool,
> > >   with no side effects.
> > >
> > > * Add a new routine, put_devmap_managed_page(), to handle checking
> > >   what kind of page it is, and what kind of refcount handling it
> > >   requires.
> > >
> > > * Rename __put_devmap_managed_page() to free_devmap_managed_page(),
> > >   and limit the functionality to unconditionally freeing a devmap
> > >   page.
> > >
> > > This is originally based on a separate patch by Ira Weiny, which
> > > applied to an early version of the put_user_page() experiments.
> > > Since then, Jérôme Glisse suggested the refactoring described above.
> > >
> > > Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> > > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> > > ---
> > >  include/linux/mm.h | 27 ++++++++++++++++---
> > >  mm/memremap.c      | 67 ++++++++++++++++++++--------------------------
> > >  2 files changed, 53 insertions(+), 41 deletions(-)
> > >
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index a2adf95b3f9c..96228376139c 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page)
> > >  #endif
> > >
> > >  #ifdef CONFIG_DEV_PAGEMAP_OPS
> > > -void __put_devmap_managed_page(struct page *page);
> > > +void free_devmap_managed_page(struct page *page);
> > >  DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
> > > -static inline bool put_devmap_managed_page(struct page *page)
> > > +
> > > +static inline bool page_is_devmap_managed(struct page *page)
> > >  {
> > >         if (!static_branch_unlikely(&devmap_managed_key))
> > >                 return false;
> > > @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page)
> > >         switch (page->pgmap->type) {
> > >         case MEMORY_DEVICE_PRIVATE:
> > >         case MEMORY_DEVICE_FS_DAX:
> > > -               __put_devmap_managed_page(page);
> > >                 return true;
> > >         default:
> > >                 break;
> > > @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page)
> > >         return false;
> > >  }
> > >
> > > +static inline bool put_devmap_managed_page(struct page *page)
> > > +{
> > > +       bool is_devmap = page_is_devmap_managed(page);
> > > +
> > > +       if (is_devmap) {
> > > +               int count = page_ref_dec_return(page);
> > > +
> > > +               /*
> > > +                * devmap page refcounts are 1-based, rather than 0-based: if
> > > +                * refcount is 1, then the page is free and the refcount is
> > > +                * stable because nobody holds a reference on the page.
> > > +                */
> > > +               if (count == 1)
> > > +                       free_devmap_managed_page(page);
> > > +               else if (!count)
> > > +                       __put_page(page);
> > > +       }
> > > +
> > > +       return is_devmap;
> > > +}
> > > +
> > >  #else /* CONFIG_DEV_PAGEMAP_OPS */
> > >  static inline bool put_devmap_managed_page(struct page *page)
> > >  {
> > > diff --git a/mm/memremap.c b/mm/memremap.c
> > > index 03ccbdfeb697..bc7e2a27d025 100644
> > > --- a/mm/memremap.c
> > > +++ b/mm/memremap.c
> > > @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> > >  EXPORT_SYMBOL_GPL(get_dev_pagemap);
> > >
> > >  #ifdef CONFIG_DEV_PAGEMAP_OPS
> > > -void __put_devmap_managed_page(struct page *page)
> > > +void free_devmap_managed_page(struct page *page)
> > >  {
> > > -       int count = page_ref_dec_return(page);
> > > +       /* Clear Active bit in case of parallel mark_page_accessed */
> > > +       __ClearPageActive(page);
> > > +       __ClearPageWaiters(page);
> > > +
> > > +       mem_cgroup_uncharge(page);
> >
> > Ugh, when did all this HMM specific manipulation sneak into the
> > generic ZONE_DEVICE path? It used to be gated by pgmap type with its
> > own put_zone_device_private_page(). For example it's certainly
> > unnecessary and might be broken (would need to check) to call
> > mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a
> > monolith and the HMM use case leaks pages into code paths that DAX
> > explicitly avoids.
> 
> It's been this way for a while and I did not react previously,
> apologies for that. I think __ClearPageActive, __ClearPageWaiters, and
> mem_cgroup_uncharge, belong behind a device-private conditional. The
> history here is:
> 
> Move some, but not all HMM specifics to hmm_devmem_free():
>     2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put
> 
> Remove the clearing of mapping since no upstream consumers needed it:
>     b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free
> 
> Add it back in once an upstream consumer arrived:
>     7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse
> 
> We're now almost entirely free of ->page_free callbacks except for
> that weird nouveau case, can that FIXME in nouveau_dmem_page_free()
> also result in killing the ->page_free() callback altogether? In the
> meantime I'm proposing a cleanup like this:

No we need the callback, cleanup looks good.

> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index ad8e4df1282b..4eae441f86c9 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem)
>         put_disk(pmem->disk);
>  }
> 
> -static void pmem_pagemap_page_free(struct page *page)
> -{
> -       wake_up_var(&page->_refcount);
> -}
> -
>  static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> -       .page_free              = pmem_pagemap_page_free,
>         .kill                   = pmem_pagemap_kill,
>         .cleanup                = pmem_pagemap_cleanup,
>  };
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03ccbdfeb697..157edb8f7cf8 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page)
>          * holds a reference on the page.
>          */
>         if (count == 1) {
> -               /* Clear Active bit in case of parallel mark_page_accessed */
> -               __ClearPageActive(page);
> -               __ClearPageWaiters(page);
> -
> -               mem_cgroup_uncharge(page);
> -
>                 /*
>                  * When a device_private page is freed, the page->mapping field
>                  * may still contain a (stale) mapping value. For example, the
> @@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page)
>                  * handled differently or not done at all, so there is no need
>                  * to clear page->mapping.
>                  */
> -               if (is_device_private_page(page))
> -                       page->mapping = NULL;
> +               if (is_device_private_page(page)) {
> +                       /* Clear Active bit in case of parallel
> mark_page_accessed */
> +                       __ClearPageActive(page);
> +                       __ClearPageWaiters(page);
> 
> -               page->pgmap->ops->page_free(page);
> +                       mem_cgroup_uncharge(page);
> +
> +                       page->mapping = NULL;
> +                       page->pgmap->ops->page_free(page);
> +               } else
> +                       wake_up_var(&page->_refcount);
>         } else if (!count)
>                 __put_page(page);
>  }
> 

Re: [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines

[John Hubbard]

On 11/13/19 3:15 AM, Jan Kara wrote:
> On Tue 12-11-19 20:26:49, John Hubbard wrote:
>> There are four locations in gup.c that have a fair amount of code
>> duplication. This means that changing one requires making the same
>> changes in four places, not to mention reading the same code four
>> times, and wondering if there are subtle differences.
>>
>> Factor out the common code into static functions, thus reducing the
>> overall line count and the code's complexity.
>>
>> Also, take the opportunity to slightly improve the efficiency of the
>> error cases, by doing a mass subtraction of the refcount, surrounded
>> by get_page()/put_page().
>>
>> Also, further simplify (slightly), by waiting until the the successful
>> end of each routine, to increment *nr.
>>
>> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> 
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 85caf76b3012..199da99e8ffc 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1969,6 +1969,34 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
>>   }
>>   #endif
>>   
>> +static int __record_subpages(struct page *page, unsigned long addr,
>> +			     unsigned long end, struct page **pages, int nr)
>> +{
>> +	int nr_recorded_pages = 0;
>> +
>> +	do {
>> +		pages[nr] = page;
>> +		nr++;
>> +		page++;
>> +		nr_recorded_pages++;
>> +	} while (addr += PAGE_SIZE, addr != end);
>> +	return nr_recorded_pages;
>> +}
> 
> Why don't you pass in already pages + nr?

Aha, that does save a function argument. Will do.

...
>> +static void __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
>> +{
>> +	*nr += nr_recorded_pages;
>> +	SetPageReferenced(head);
>> +}
> 
> I don't find this last helper very useful. It seems to muddy water more
> than necessary...

Yes, I suspect it's rather unloved, and the fact that it was hard to accurately
name should have been a big hint to not do it. I'll remove the helper and
put the lines back in directly.


thanks,
-- 
John Hubbard
NVIDIA

> 
> Other than that the cleanup looks nice to me.
> 
> 								Honza
> 

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[John Hubbard]

On 11/13/19 2:43 AM, Jan Kara wrote:
...
> How does FOLL_PIN result in grabbing (at least normal, for now) page reference?
> I didn't find that anywhere in this patch but it is a prerequisite to
> converting any user to pin_user_pages() interface, right?


ohhh, I messed up on this intermediate patch: it doesn't quite stand alone as
it should, as you noticed. To correct this, I can do one of the following:

a) move the new pin*() routines into the later patch 16 ("mm/gup:
track FOLL_PIN pages"), or

b) do a temporary thing here, such as setting FOLL_GET and adding a TODO,
within the pin*() implementations. And this switching it over to FOLL_PIN
in patch 16.

I'm thinking (a) is less error-prone, so I'm going with that unless someone
points out that that is stupid. :)


...
> I was somewhat wondering about the number of functions you add here. So we
> have:> 
> pin_user_pages()
> pin_user_pages_fast()
> pin_user_pages_remote()
> 
> and then longterm variants:
> 
> pin_longterm_pages()
> pin_longterm_pages_fast()
> pin_longterm_pages_remote()
> 
> and obviously we have gup like:
> get_user_pages()
> get_user_pages_fast()
> get_user_pages_remote()
> ... and some other gup variants ...
> 
> I think we really should have pin_* vs get_* variants as they are very
> different in terms of guarantees and after conversion, any use of get_*
> variant in non-mm code should be closely scrutinized. OTOH pin_longterm_*
> don't look *that* useful to me and just using pin_* instead with
> FOLL_LONGTERM flag would look OK to me and somewhat reduce the number of
> functions which is already large enough? What do people think? I don't feel
> too strongly about this but wanted to bring this up.
> 
> 								Honza

Sounds just right to me, and I see that Dan and Ira also like it.
So I'll proceed with that.

thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM)

[John Hubbard]

On 11/13/19 11:09 AM, Ira Weiny wrote:
...
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 82e7e4ce5027..90f5f95ee7ac 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1756,11 +1756,11 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>>   		struct vm_area_struct **vmas)
>>   {
>>   	/*
>> -	 * FOLL_PIN must only be set internally by the pin_user_page*() and
>> -	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
>> -	 * with an assertion:
>> +	 * FOLL_PIN and FOLL_LONGTERM must only be set internally by the
>> +	 * pin_user_page*() and pin_longterm_*() APIs, never directly by the
>> +	 * caller, so enforce that with an assertion:
>>   	 */
>> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
>> +	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_LONGTERM)))
> 
> Don't we want to block FOLL_LONGTERM in get_user_pages_fast() as well after all
> this?
> 

Yes. But with the latest idea to restore FOLL_LONGTERM to its original glory,
that won't be an issue in the next version. heh.


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN

[John Hubbard]

On 11/13/19 3:22 PM, John Hubbard wrote:
> On 11/13/19 2:43 AM, Jan Kara wrote:
> ...
>> How does FOLL_PIN result in grabbing (at least normal, for now) page reference?
>> I didn't find that anywhere in this patch but it is a prerequisite to
>> converting any user to pin_user_pages() interface, right?
> 
> 
> ohhh, I messed up on this intermediate patch: it doesn't quite stand alone as
> it should, as you noticed. To correct this, I can do one of the following:
> 
> a) move the new pin*() routines into the later patch 16 ("mm/gup:
> track FOLL_PIN pages"), or
> 
> b) do a temporary thing here, such as setting FOLL_GET and adding a TODO,
> within the pin*() implementations. And this switching it over to FOLL_PIN
> in patch 16.
> 
> I'm thinking (a) is less error-prone, so I'm going with that unless someone
> points out that that is stupid. :)
> 

OK, just to save anyone from wasting time reading the above: (a) is, in fact,
stupid, after all. ha. That is because pin_user_pages() is called in the 
intervening patches.
 
So anyway, I'll work out an ordering to fix it up, it's not complicated.


thanks,
-- 
John Hubbard
NVIDIA