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mm: move FOLL_* defs to mm_types.h
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Move FOLL_* definitions to linux/mm_types.h to make them more accessible
without having to drag in all of linux/mm.h and everything that drags in
too[1].

Link: https://lkml.kernel.org/r/2161258.1671657894@warthog.procyon.org.uk
Signed-off-by: David Howells <dhowells@redhat.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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David Howells authored and Andrew Morton committed Jan 19, 2023
1 parent 0b7b870 commit b505417
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75 changes: 0 additions & 75 deletions include/linux/mm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3057,81 +3057,6 @@ static inline vm_fault_t vmf_error(int err)
struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int foll_flags);

#define FOLL_WRITE 0x01 /* check pte is writable */
#define FOLL_TOUCH 0x02 /* mark page accessed */
#define FOLL_GET 0x04 /* do get_page on page */
#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
* and return without waiting upon it */
#define FOLL_NOFAULT 0x80 /* do not fault in pages */
#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
#define FOLL_ANON 0x8000 /* don't do file mappings */
#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
#define FOLL_PCI_P2PDMA 0x100000 /* allow returning PCI P2PDMA pages */
#define FOLL_INTERRUPTIBLE 0x200000 /* allow interrupts from generic signals */

/*
* FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
* other. Here is what they mean, and how to use them:
*
* FOLL_LONGTERM indicates that the page will be held for an indefinite time
* period _often_ under userspace control. This is in contrast to
* iov_iter_get_pages(), whose usages are transient.
*
* FIXME: For pages which are part of a filesystem, mappings are subject to the
* lifetime enforced by the filesystem and we need guarantees that longterm
* users like RDMA and V4L2 only establish mappings which coordinate usage with
* the filesystem. Ideas for this coordination include revoking the longterm
* pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was
* added after the problem with filesystems was found FS DAX VMAs are
* specifically failed. Filesystem pages are still subject to bugs and use of
* FOLL_LONGTERM should be avoided on those pages.
*
* FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call.
* Currently only get_user_pages() and get_user_pages_fast() support this flag
* and calls to get_user_pages_[un]locked are specifically not allowed. This
* is due to an incompatibility with the FS DAX check and
* FAULT_FLAG_ALLOW_RETRY.
*
* In the CMA case: long term pins in a CMA region would unnecessarily fragment
* that region. And so, CMA attempts to migrate the page before pinning, when
* FOLL_LONGTERM is specified.
*
* FOLL_PIN indicates that a special kind of tracking (not just page->_refcount,
* but an additional pin counting system) will be invoked. This is intended for
* anything that gets a page reference and then touches page data (for example,
* Direct IO). This lets the filesystem know that some non-file-system entity is
* potentially changing the pages' data. In contrast to FOLL_GET (whose pages
* are released via put_page()), FOLL_PIN pages must be released, ultimately, by
* a call to unpin_user_page().
*
* FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different
* and separate refcounting mechanisms, however, and that means that each has
* its own acquire and release mechanisms:
*
* FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
*
* FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to release.
*
* FOLL_PIN and FOLL_GET are mutually exclusive for a given function call.
* (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based
* calls applied to them, and that's perfectly OK. This is a constraint on the
* callers, not on the pages.)
*
* FOLL_PIN should be set internally by the pin_user_pages*() APIs, never
* directly by the caller. That's in order to help avoid mismatches when
* releasing pages: get_user_pages*() pages must be released via put_page(),
* while pin_user_pages*() pages must be released via unpin_user_page().
*
* Please see Documentation/core-api/pin_user_pages.rst for more information.
*/

static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
{
if (vm_fault & VM_FAULT_OOM)
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75 changes: 75 additions & 0 deletions include/linux/mm_types.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1085,4 +1085,79 @@ enum fault_flag {

typedef unsigned int __bitwise zap_flags_t;

/*
* FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
* other. Here is what they mean, and how to use them:
*
* FOLL_LONGTERM indicates that the page will be held for an indefinite time
* period _often_ under userspace control. This is in contrast to
* iov_iter_get_pages(), whose usages are transient.
*
* FIXME: For pages which are part of a filesystem, mappings are subject to the
* lifetime enforced by the filesystem and we need guarantees that longterm
* users like RDMA and V4L2 only establish mappings which coordinate usage with
* the filesystem. Ideas for this coordination include revoking the longterm
* pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was
* added after the problem with filesystems was found FS DAX VMAs are
* specifically failed. Filesystem pages are still subject to bugs and use of
* FOLL_LONGTERM should be avoided on those pages.
*
* FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call.
* Currently only get_user_pages() and get_user_pages_fast() support this flag
* and calls to get_user_pages_[un]locked are specifically not allowed. This
* is due to an incompatibility with the FS DAX check and
* FAULT_FLAG_ALLOW_RETRY.
*
* In the CMA case: long term pins in a CMA region would unnecessarily fragment
* that region. And so, CMA attempts to migrate the page before pinning, when
* FOLL_LONGTERM is specified.
*
* FOLL_PIN indicates that a special kind of tracking (not just page->_refcount,
* but an additional pin counting system) will be invoked. This is intended for
* anything that gets a page reference and then touches page data (for example,
* Direct IO). This lets the filesystem know that some non-file-system entity is
* potentially changing the pages' data. In contrast to FOLL_GET (whose pages
* are released via put_page()), FOLL_PIN pages must be released, ultimately, by
* a call to unpin_user_page().
*
* FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different
* and separate refcounting mechanisms, however, and that means that each has
* its own acquire and release mechanisms:
*
* FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
*
* FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to release.
*
* FOLL_PIN and FOLL_GET are mutually exclusive for a given function call.
* (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based
* calls applied to them, and that's perfectly OK. This is a constraint on the
* callers, not on the pages.)
*
* FOLL_PIN should be set internally by the pin_user_pages*() APIs, never
* directly by the caller. That's in order to help avoid mismatches when
* releasing pages: get_user_pages*() pages must be released via put_page(),
* while pin_user_pages*() pages must be released via unpin_user_page().
*
* Please see Documentation/core-api/pin_user_pages.rst for more information.
*/

#define FOLL_WRITE 0x01 /* check pte is writable */
#define FOLL_TOUCH 0x02 /* mark page accessed */
#define FOLL_GET 0x04 /* do get_page on page */
#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
* and return without waiting upon it */
#define FOLL_NOFAULT 0x80 /* do not fault in pages */
#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
#define FOLL_ANON 0x8000 /* don't do file mappings */
#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
#define FOLL_PCI_P2PDMA 0x100000 /* allow returning PCI P2PDMA pages */
#define FOLL_INTERRUPTIBLE 0x200000 /* allow interrupts from generic signals */

#endif /* _LINUX_MM_TYPES_H */

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