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Message-Id: <20171204160046.564227420@linuxfoundation.org>
Date: Mon, 4 Dec 2017 16:59:33 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
Christoph Hellwig <hch@....de>,
Doug Ledford <dledford@...hat.com>,
Hal Rosenstock <hal.rosenstock@...il.com>,
Inki Dae <inki.dae@...sung.com>, Jan Kara <jack@...e.cz>,
Jason Gunthorpe <jgg@...lanox.com>,
Jeff Moyer <jmoyer@...hat.com>,
Joonyoung Shim <jy0922.shim@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Mel Gorman <mgorman@...e.de>,
Ross Zwisler <ross.zwisler@...ux.intel.com>,
Sean Hefty <sean.hefty@...el.com>,
Seung-Woo Kim <sw0312.kim@...sung.com>,
Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 09/95] mm: introduce get_user_pages_longterm
4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dan Williams <dan.j.williams@...el.com>
commit 2bb6d2837083de722bfdc369cb0d76ce188dd9b4 upstream.
Patch series "introduce get_user_pages_longterm()", v2.
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.
This patch (of 4):
Until there is a solution to the dma-to-dax vs truncate problem it is
not safe to allow long standing memory registrations against
filesytem-dax vmas. Device-dax vmas do not have this problem and are
explicitly allowed.
This is temporary until a "memory registration with layout-lease"
mechanism can be implemented for the affected sub-systems (RDMA and
V4L2).
[akpm@...ux-foundation.org: use kcalloc()]
Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Suggested-by: Christoph Hellwig <hch@....de>
Cc: Doug Ledford <dledford@...hat.com>
Cc: Hal Rosenstock <hal.rosenstock@...il.com>
Cc: Inki Dae <inki.dae@...sung.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Jason Gunthorpe <jgg@...lanox.com>
Cc: Jeff Moyer <jmoyer@...hat.com>
Cc: Joonyoung Shim <jy0922.shim@...sung.com>
Cc: Kyungmin Park <kyungmin.park@...sung.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: Sean Hefty <sean.hefty@...el.com>
Cc: Seung-Woo Kim <sw0312.kim@...sung.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
include/linux/fs.h | 14 +++++++++++
include/linux/mm.h | 13 ++++++++++
mm/gup.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 91 insertions(+)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3175,6 +3175,20 @@ static inline bool vma_is_dax(struct vm_
return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
}
+static inline bool vma_is_fsdax(struct vm_area_struct *vma)
+{
+ struct inode *inode;
+
+ if (!vma->vm_file)
+ return false;
+ if (!vma_is_dax(vma))
+ return false;
+ inode = file_inode(vma->vm_file);
+ if (inode->i_mode == S_IFCHR)
+ return false; /* device-dax */
+ return true;
+}
+
static inline int iocb_flags(struct file *file)
{
int res = 0;
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1368,6 +1368,19 @@ long get_user_pages_locked(unsigned long
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);
+#ifdef CONFIG_FS_DAX
+long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
+ unsigned int gup_flags, struct page **pages,
+ struct vm_area_struct **vmas);
+#else
+static inline long get_user_pages_longterm(unsigned long start,
+ unsigned long nr_pages, unsigned int gup_flags,
+ struct page **pages, struct vm_area_struct **vmas)
+{
+ return get_user_pages(start, nr_pages, gup_flags, pages, vmas);
+}
+#endif /* CONFIG_FS_DAX */
+
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages);
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1095,6 +1095,70 @@ long get_user_pages(unsigned long start,
}
EXPORT_SYMBOL(get_user_pages);
+#ifdef CONFIG_FS_DAX
+/*
+ * This is the same as get_user_pages() in that it assumes we are
+ * operating on the current task's mm, but it goes further to validate
+ * that the vmas associated with the address range are suitable for
+ * longterm elevated page reference counts. For example, filesystem-dax
+ * mappings are subject to the lifetime enforced by the filesystem and
+ * we need guarantees that longterm users like RDMA and V4L2 only
+ * establish mappings that have a kernel enforced revocation mechanism.
+ *
+ * "longterm" == userspace controlled elevated page count lifetime.
+ * Contrast this to iov_iter_get_pages() usages which are transient.
+ */
+long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
+ unsigned int gup_flags, struct page **pages,
+ struct vm_area_struct **vmas_arg)
+{
+ struct vm_area_struct **vmas = vmas_arg;
+ struct vm_area_struct *vma_prev = NULL;
+ long rc, i;
+
+ if (!pages)
+ return -EINVAL;
+
+ if (!vmas) {
+ vmas = kcalloc(nr_pages, sizeof(struct vm_area_struct *),
+ GFP_KERNEL);
+ if (!vmas)
+ return -ENOMEM;
+ }
+
+ rc = get_user_pages(start, nr_pages, gup_flags, pages, vmas);
+
+ for (i = 0; i < rc; i++) {
+ struct vm_area_struct *vma = vmas[i];
+
+ if (vma == vma_prev)
+ continue;
+
+ vma_prev = vma;
+
+ if (vma_is_fsdax(vma))
+ break;
+ }
+
+ /*
+ * Either get_user_pages() failed, or the vma validation
+ * succeeded, in either case we don't need to put_page() before
+ * returning.
+ */
+ if (i >= rc)
+ goto out;
+
+ for (i = 0; i < rc; i++)
+ put_page(pages[i]);
+ rc = -EOPNOTSUPP;
+out:
+ if (vmas != vmas_arg)
+ kfree(vmas);
+ return rc;
+}
+EXPORT_SYMBOL(get_user_pages_longterm);
+#endif /* CONFIG_FS_DAX */
+
/**
* populate_vma_page_range() - populate a range of pages in the vma.
* @vma: target vma
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