[PATCH v2 0/2] mm/gup, media/ivtv: introduce pin_user_pages_unlocked

[PATCH v2 0/2] mm/gup, media/ivtv: introduce pin_user_pages_unlocked

[John Hubbard]

Hi,

Here is a v2 that includes a small change that follows from Souptick's
review of another very similar patchset (that added
pin_user_pages_locked()) [1].

This applies on top of today's linux.git (5.7-rc7+).

Changes since v1: added an assert-and-return to the corresponding
get_user_pages_unlocked() call, to keep out any externally set
FOLL_PIN flag.

These patches are getting merged via Andrew's linux-mm tree, due to
adding a new pin_user_pages*() variant to gup.c. However, it would be
nice if anyone from IVTV or linux-media could provide some run time
testing, maybe even a Tested-by.

I've run this patchset through non-destructive xfstests, and a few
other things such as LTP. However, I'm not set up for IVTV specific
testing.

[1] https://lore.kernel.org/r/d11d52f8-d54c-bb45-bde9-198235a03921@nvidia.com


John Hubbard (2):
  mm/gup: introduce pin_user_pages_unlocked
  ivtv: convert get_user_pages() --> pin_user_pages()

 drivers/media/pci/ivtv/ivtv-udma.c | 19 ++++++-------------
 drivers/media/pci/ivtv/ivtv-yuv.c  | 17 ++++++-----------
 drivers/media/pci/ivtv/ivtvfb.c    |  4 ++--
 include/linux/mm.h                 |  2 ++
 mm/gup.c                           | 23 +++++++++++++++++++++++
 5 files changed, 39 insertions(+), 26 deletions(-)


base-commit: bdc48fa11e46f867ea4d75fa59ee87a7f48be144
-- 
2.26.2

[PATCH v2 1/2] mm/gup: introduce pin_user_pages_unlocked

[John Hubbard]

Introduce pin_user_pages_unlocked(), which is nearly identical to the
get_user_pages_unlocked() that it wraps, except that it sets FOLL_PIN
and rejects FOLL_GET.

As with other pairs of get_user_pages*() and pin_user_pages() API calls,
it's prudent to assert that FOLL_PIN is *not* set in the
get_user_pages*() call, so add that as part of this.

Cc: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h |  2 ++
 mm/gup.c           | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f3fe7371855c..a84befdb54b2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1713,6 +1713,8 @@ 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,
 		    struct page **pages, unsigned int gup_flags);
+long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+		    struct page **pages, unsigned int gup_flags);
 
 int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages);
diff --git a/mm/gup.c b/mm/gup.c
index 87a6a59fe667..8ae5d09adb6b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2030,6 +2030,12 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 	 */
 	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
 		return -EINVAL;
+	/*
+	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
+	 * never directly by the caller, so enforce that:
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+		return -EINVAL;
 
 	down_read(&mm->mmap_sem);
 	ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
@@ -2939,3 +2945,20 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
 				     pages, vmas, gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages);
+
+/*
+ * pin_user_pages_unlocked() is the FOLL_PIN variant of
+ * get_user_pages_unlocked(). Behavior is the same, except that this one sets
+ * FOLL_PIN and rejects FOLL_GET.
+ */
+long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+			     struct page **pages, unsigned int gup_flags)
+{
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages_unlocked);
-- 
2.26.2

[PATCH v2 2/2] ivtv: convert get_user_pages() --> pin_user_pages()

[John Hubbard]

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/media/pci/ivtv/ivtv-udma.c | 19 ++++++-------------
 drivers/media/pci/ivtv/ivtv-yuv.c  | 17 ++++++-----------
 drivers/media/pci/ivtv/ivtvfb.c    |  4 ++--
 3 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/drivers/media/pci/ivtv/ivtv-udma.c b/drivers/media/pci/ivtv/ivtv-udma.c
index 5f8883031c9c..0d8372cc364a 100644
--- a/drivers/media/pci/ivtv/ivtv-udma.c
+++ b/drivers/media/pci/ivtv/ivtv-udma.c
@@ -92,7 +92,7 @@ int ivtv_udma_setup(struct ivtv *itv, unsigned long ivtv_dest_addr,
 {
 	struct ivtv_dma_page_info user_dma;
 	struct ivtv_user_dma *dma = &itv->udma;
-	int i, err;
+	int err;
 
 	IVTV_DEBUG_DMA("ivtv_udma_setup, dst: 0x%08x\n", (unsigned int)ivtv_dest_addr);
 
@@ -111,16 +111,15 @@ int ivtv_udma_setup(struct ivtv *itv, unsigned long ivtv_dest_addr,
 		return -EINVAL;
 	}
 
-	/* Get user pages for DMA Xfer */
-	err = get_user_pages_unlocked(user_dma.uaddr, user_dma.page_count,
+	/* Pin user pages for DMA Xfer */
+	err = pin_user_pages_unlocked(user_dma.uaddr, user_dma.page_count,
 			dma->map, FOLL_FORCE);
 
 	if (user_dma.page_count != err) {
 		IVTV_DEBUG_WARN("failed to map user pages, returned %d instead of %d\n",
 			   err, user_dma.page_count);
 		if (err >= 0) {
-			for (i = 0; i < err; i++)
-				put_page(dma->map[i]);
+			unpin_user_pages(dma->map, err);
 			return -EINVAL;
 		}
 		return err;
@@ -130,9 +129,7 @@ int ivtv_udma_setup(struct ivtv *itv, unsigned long ivtv_dest_addr,
 
 	/* Fill SG List with new values */
 	if (ivtv_udma_fill_sg_list(dma, &user_dma, 0) < 0) {
-		for (i = 0; i < dma->page_count; i++) {
-			put_page(dma->map[i]);
-		}
+		unpin_user_pages(dma->map, dma->page_count);
 		dma->page_count = 0;
 		return -ENOMEM;
 	}
@@ -153,7 +150,6 @@ int ivtv_udma_setup(struct ivtv *itv, unsigned long ivtv_dest_addr,
 void ivtv_udma_unmap(struct ivtv *itv)
 {
 	struct ivtv_user_dma *dma = &itv->udma;
-	int i;
 
 	IVTV_DEBUG_INFO("ivtv_unmap_user_dma\n");
 
@@ -169,10 +165,7 @@ void ivtv_udma_unmap(struct ivtv *itv)
 	/* sync DMA */
 	ivtv_udma_sync_for_cpu(itv);
 
-	/* Release User Pages */
-	for (i = 0; i < dma->page_count; i++) {
-		put_page(dma->map[i]);
-	}
+	unpin_user_pages(dma->map, dma->page_count);
 	dma->page_count = 0;
 }
 
diff --git a/drivers/media/pci/ivtv/ivtv-yuv.c b/drivers/media/pci/ivtv/ivtv-yuv.c
index cd2fe2d444c0..5f7dc9771f8d 100644
--- a/drivers/media/pci/ivtv/ivtv-yuv.c
+++ b/drivers/media/pci/ivtv/ivtv-yuv.c
@@ -30,7 +30,6 @@ static int ivtv_yuv_prep_user_dma(struct ivtv *itv, struct ivtv_user_dma *dma,
 	struct yuv_playback_info *yi = &itv->yuv_info;
 	u8 frame = yi->draw_frame;
 	struct yuv_frame_info *f = &yi->new_frame_info[frame];
-	int i;
 	int y_pages, uv_pages;
 	unsigned long y_buffer_offset, uv_buffer_offset;
 	int y_decode_height, uv_decode_height, y_size;
@@ -62,12 +61,12 @@ static int ivtv_yuv_prep_user_dma(struct ivtv *itv, struct ivtv_user_dma *dma,
 	ivtv_udma_get_page_info (&y_dma, (unsigned long)args->y_source, 720 * y_decode_height);
 	ivtv_udma_get_page_info (&uv_dma, (unsigned long)args->uv_source, 360 * uv_decode_height);
 
-	/* Get user pages for DMA Xfer */
-	y_pages = get_user_pages_unlocked(y_dma.uaddr,
+	/* Pin user pages for DMA Xfer */
+	y_pages = pin_user_pages_unlocked(y_dma.uaddr,
 			y_dma.page_count, &dma->map[0], FOLL_FORCE);
 	uv_pages = 0; /* silence gcc. value is set and consumed only if: */
 	if (y_pages == y_dma.page_count) {
-		uv_pages = get_user_pages_unlocked(uv_dma.uaddr,
+		uv_pages = pin_user_pages_unlocked(uv_dma.uaddr,
 				uv_dma.page_count, &dma->map[y_pages],
 				FOLL_FORCE);
 	}
@@ -81,8 +80,7 @@ static int ivtv_yuv_prep_user_dma(struct ivtv *itv, struct ivtv_user_dma *dma,
 				 uv_pages, uv_dma.page_count);
 
 			if (uv_pages >= 0) {
-				for (i = 0; i < uv_pages; i++)
-					put_page(dma->map[y_pages + i]);
+				unpin_user_pages(&dma->map[y_pages], uv_pages);
 				rc = -EFAULT;
 			} else {
 				rc = uv_pages;
@@ -93,8 +91,7 @@ static int ivtv_yuv_prep_user_dma(struct ivtv *itv, struct ivtv_user_dma *dma,
 				 y_pages, y_dma.page_count);
 		}
 		if (y_pages >= 0) {
-			for (i = 0; i < y_pages; i++)
-				put_page(dma->map[i]);
+			unpin_user_pages(dma->map, y_pages);
 			/*
 			 * Inherit the -EFAULT from rc's
 			 * initialization, but allow it to be
@@ -112,9 +109,7 @@ static int ivtv_yuv_prep_user_dma(struct ivtv *itv, struct ivtv_user_dma *dma,
 	/* Fill & map SG List */
 	if (ivtv_udma_fill_sg_list (dma, &uv_dma, ivtv_udma_fill_sg_list (dma, &y_dma, 0)) < 0) {
 		IVTV_DEBUG_WARN("could not allocate bounce buffers for highmem userspace buffers\n");
-		for (i = 0; i < dma->page_count; i++) {
-			put_page(dma->map[i]);
-		}
+		unpin_user_pages(dma->map, dma->page_count);
 		dma->page_count = 0;
 		return -ENOMEM;
 	}
diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
index 0c2859844081..e2d56dca5be4 100644
--- a/drivers/media/pci/ivtv/ivtvfb.c
+++ b/drivers/media/pci/ivtv/ivtvfb.c
@@ -281,10 +281,10 @@ static int ivtvfb_prep_dec_dma_to_device(struct ivtv *itv,
 	/* Map User DMA */
 	if (ivtv_udma_setup(itv, ivtv_dest_addr, userbuf, size_in_bytes) <= 0) {
 		mutex_unlock(&itv->udma.lock);
-		IVTVFB_WARN("ivtvfb_prep_dec_dma_to_device, Error with get_user_pages: %d bytes, %d pages returned\n",
+		IVTVFB_WARN("ivtvfb_prep_dec_dma_to_device, Error with pin_user_pages: %d bytes, %d pages returned\n",
 			       size_in_bytes, itv->udma.page_count);
 
-		/* get_user_pages must have failed completely */
+		/* pin_user_pages must have failed completely */
 		return -EIO;
 	}
 
-- 
2.26.2