Commit 2bb6d283 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds

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).

[akpm@linux-foundation.org: use kcalloc()]
Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: 3565fce3 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Suggested-by: default avatarChristoph Hellwig <hch@lst.de>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Hal Rosenstock <hal.rosenstock@gmail.com>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9702cffd
......@@ -3194,6 +3194,20 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
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;
......
......@@ -1380,6 +1380,19 @@ 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);
#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);
......
......@@ -1095,6 +1095,70 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
}
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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