The patch titled
Subject: mm: introduce get_user_pages_longterm
has been added to the -mm tree. Its filename is
mm-introduce-get_user_pages_longterm.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-introduce-get_user_pages_longterm.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-introduce-get_user_pages_longterm.patch
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------------------------------------------------------
From: Dan Williams <dan.j.williams@xxxxxxxxx>
Subject: mm: introduce get_user_pages_longterm
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).
Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Suggested-by: Christoph Hellwig <hch@xxxxxx>
Cc: Doug Ledford <dledford@xxxxxxxxxx>
Cc: Hal Rosenstock <hal.rosenstock@xxxxxxxxx>
Cc: Inki Dae <inki.dae@xxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Joonyoung Shim <jy0922.shim@xxxxxxxxxxx>
Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Sean Hefty <sean.hefty@xxxxxxxxx>
Cc: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/fs.h | 14 +++++++++
include/linux/mm.h | 13 ++++++++
mm/gup.c | 64 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 91 insertions(+)
diff -puN include/linux/fs.h~mm-introduce-get_user_pages_longterm include/linux/fs.h
--- a/include/linux/fs.h~mm-introduce-get_user_pages_longterm
+++ a/include/linux/fs.h
@@ -3194,6 +3194,20 @@ 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;
diff -puN include/linux/mm.h~mm-introduce-get_user_pages_longterm include/linux/mm.h
--- a/include/linux/mm.h~mm-introduce-get_user_pages_longterm
+++ a/include/linux/mm.h
@@ -1380,6 +1380,19 @@ 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);
diff -puN mm/gup.c~mm-introduce-get_user_pages_longterm mm/gup.c
--- a/mm/gup.c~mm-introduce-get_user_pages_longterm
+++ a/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 = kzalloc(sizeof(struct vm_area_struct *) * nr_pages,
+ 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
_
Patches currently in -mm which might be from dan.j.williams@xxxxxxxxx are
mm-fix-device-dax-pud-write-faults-triggered-by-get_user_pages.patch
mm-fix-device-dax-pud-write-faults-triggered-by-get_user_pages-v3.patch
mm-switch-to-define-pmd_write-instead-of-__have_arch_pmd_write.patch
mm-replace-pud_write-with-pud_access_permitted-in-fault-gup-paths.patch
mm-replace-pud_write-with-pud_access_permitted-in-fault-gup-paths-v3.patch
mm-replace-pmd_write-with-pmd_access_permitted-in-fault-gup-paths.patch
mm-replace-pte_write-with-pte_access_permitted-in-fault-gup-paths.patch
mm-hugetlbfs-introduce-split-to-vm_operations_struct.patch
device-dax-implement-split-to-catch-invalid-munmap-attempts.patch
mm-introduce-get_user_pages_longterm.patch
mm-fail-get_vaddr_frames-for-filesystem-dax-mappings.patch
v4l2-disable-filesystem-dax-mapping-support.patch
ib-core-disable-memory-registration-of-fileystem-dax-vmas.patch
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