* [PATCH v3 0/4] introduce get_user_pages_longterm()
@ 2017-11-29 18:05 Dan Williams
2017-11-29 18:05 ` [PATCH v3 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings Dan Williams
2017-11-29 18:05 ` [PATCH v3 3/4] [media] v4l2: disable filesystem-dax mapping support Dan Williams
0 siblings, 2 replies; 3+ messages in thread
From: Dan Williams @ 2017-11-29 18:05 UTC (permalink / raw)
To: akpm
Cc: Inki Dae, Jan Kara, Joonyoung Shim, linux-nvdimm, linux-rdma,
linux-kernel, Seung-Woo Kim, Jeff Moyer, stable, Hal Rosenstock,
Jason Gunthorpe, linux-mm, Doug Ledford, Mel Gorman,
Ross Zwisler, Kyungmin Park, Sean Hefty, Mauro Carvalho Chehab,
hch, Vlastimil Babka, linux-media
Changes since v2 [1]:
* Add a comment for the vma_is_fsdax() check in get_vaddr_frames() (Jan)
* Collect Jan's Reviewed-by.
* Rebased on v4.15-rc1
[1]: https://lists.01.org/pipermail/linux-nvdimm/2017-November/013295.html
The summary text below is unchanged from v2.
---
Andrew,
Here is a new get_user_pages api for cases where a driver intends to
keep an elevated page count indefinitely. This is distinct from usages
like iov_iter_get_pages where the elevated page counts are transient.
The iov_iter_get_pages cases immediately turn around and submit the
pages to a device driver which will put_page when the i/o operation
completes (under kernel control).
In the longterm case userspace is responsible for dropping the page
reference at some undefined point in the future. This is untenable for
filesystem-dax case where the filesystem is in control of the lifetime
of the block / page and needs reasonable limits on how long it can wait
for pages in a mapping to become idle.
Fixing filesystems to actually wait for dax pages to be idle before
blocks from a truncate/hole-punch operation are repurposed is saved for
a later patch series.
Also, allowing longterm registration of dax mappings is a future patch
series that introduces a "map with lease" semantic where the kernel can
revoke a lease and force userspace to drop its page references.
I have also tagged these for -stable to purposely break cases that might
assume that longterm memory registrations for filesystem-dax mappings
were supported by the kernel. The behavior regression this policy change
implies is one of the reasons we maintain the "dax enabled. Warning:
EXPERIMENTAL, use at your own risk" notification when mounting a
filesystem in dax mode.
It is worth noting the device-dax interface does not suffer the same
constraints since it does not support file space management operations
like hole-punch.
---
Dan Williams (4):
mm: introduce get_user_pages_longterm
mm: fail get_vaddr_frames() for filesystem-dax mappings
[media] v4l2: disable filesystem-dax mapping support
IB/core: disable memory registration of fileystem-dax vmas
drivers/infiniband/core/umem.c | 2 -
drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +-
include/linux/fs.h | 14 ++++++
include/linux/mm.h | 13 ++++++
mm/frame_vector.c | 12 +++++
mm/gup.c | 64 +++++++++++++++++++++++++++++
6 files changed, 107 insertions(+), 3 deletions(-)
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v3 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings
2017-11-29 18:05 [PATCH v3 0/4] introduce get_user_pages_longterm() Dan Williams
@ 2017-11-29 18:05 ` Dan Williams
2017-11-29 18:05 ` [PATCH v3 3/4] [media] v4l2: disable filesystem-dax mapping support Dan Williams
1 sibling, 0 replies; 3+ messages in thread
From: Dan Williams @ 2017-11-29 18:05 UTC (permalink / raw)
To: akpm
Cc: Jan Kara, Joonyoung Shim, linux-nvdimm, Seung-Woo Kim,
linux-kernel, stable, Inki Dae, linux-mm, Kyungmin Park,
Mel Gorman, Mauro Carvalho Chehab, hch, Vlastimil Babka,
linux-media
Until there is a solution to the dma-to-dax vs truncate problem it is
not safe to allow V4L2, Exynos, and other frame vector users to create
long standing / irrevocable memory registrations against filesytem-dax
vmas.
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Cc: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
mm/frame_vector.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 2f98df0d460e..297c7238f7d4 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -53,6 +53,18 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
ret = -EFAULT;
goto out;
}
+
+ /*
+ * While get_vaddr_frames() could be used for transient (kernel
+ * controlled lifetime) pinning of memory pages all current
+ * users establish long term (userspace controlled lifetime)
+ * page pinning. Treat get_vaddr_frames() like
+ * get_user_pages_longterm() and disallow it for filesystem-dax
+ * mappings.
+ */
+ if (vma_is_fsdax(vma))
+ return -EOPNOTSUPP;
+
if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
vec->got_ref = true;
vec->is_pfns = false;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH v3 3/4] [media] v4l2: disable filesystem-dax mapping support
2017-11-29 18:05 [PATCH v3 0/4] introduce get_user_pages_longterm() Dan Williams
2017-11-29 18:05 ` [PATCH v3 2/4] mm: fail get_vaddr_frames() for filesystem-dax mappings Dan Williams
@ 2017-11-29 18:05 ` Dan Williams
1 sibling, 0 replies; 3+ messages in thread
From: Dan Williams @ 2017-11-29 18:05 UTC (permalink / raw)
To: akpm
Cc: Jan Kara, linux-nvdimm, linux-kernel, stable, linux-mm,
Mauro Carvalho Chehab, hch, linux-media
V4L2 memory registrations are incompatible with filesystem-dax that
needs the ability to revoke dma access to a mapping at will, or
otherwise allow the kernel to wait for completion of DMA. The
filesystem-dax implementation breaks the traditional solution of
truncate of active file backed mappings since there is no page-cache
page we can orphan to sustain ongoing DMA.
If v4l2 wants to support long lived DMA mappings it needs to arrange to
hold a file lease or use some other mechanism so that the kernel can
coordinate revoking DMA access when the filesystem needs to truncate
mappings.
Reported-by: Jan Kara <jack@suse.cz>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Cc: <stable@vger.kernel.org>
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
index 0b5c43f7e020..f412429cf5ba 100644
--- a/drivers/media/v4l2-core/videobuf-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
@@ -185,12 +185,13 @@ 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,
+ err = get_user_pages_longterm(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, dma->nr_pages);
+ dprintk(1, "get_user_pages_longterm: err=%d [%d]\n", err,
+ dma->nr_pages);
return err < 0 ? err : -EINVAL;
}
return 0;
^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-11-29 18:14 UTC | newest]
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