mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM
As it says in the updated comment in gup.c: current FOLL_LONGTERM
behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS
DAX check requirement on vmas.
However, the corresponding restriction in get_user_pages_remote() was
slightly stricter than is actually required: it forbade all
FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
that do not set the "locked" arg.
Update the code and comments to loosen the restriction, allowing
FOLL_LONGTERM in some cases.
Also, copy the DAX check ("if a VMA is DAX, don't allow long term
pinning") from the VFIO call site, all the way into the internals of
get_user_pages_remote() and __gup_longterm_locked(). That is:
get_user_pages_remote() calls __gup_longterm_locked(), which in turn
calls check_dax_vmas(). This check will then be removed from the VFIO
call site in a subsequent patch.
Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and
to Dan Williams for helping clarify the DAX refactoring.
Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Björn Töpel <bjorn.topel@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Leon Romanovsky <leonro@mellanox.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
John Hubbard
Linus Torvalds
parent
1023369c6e
commit
c4237f8b1f
174
mm/gup.c
174
mm/gup.c
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@ -1111,88 +1111,6 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
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return pages_done;
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}
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/*
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* get_user_pages_remote() - pin user pages in memory
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* @tsk: the task_struct to use for page fault accounting, or
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* NULL if faults are not to be recorded.
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* @mm: mm_struct of target mm
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* @start: starting user address
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* @nr_pages: number of pages from start to pin
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* @gup_flags: flags modifying lookup behaviour
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long. Or NULL, if caller
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* only intends to ensure the pages are faulted in.
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* @vmas: array of pointers to vmas corresponding to each page.
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* Or NULL if the caller does not require them.
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* @locked: pointer to lock flag indicating whether lock is held and
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* subsequently whether VM_FAULT_RETRY functionality can be
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* utilised. Lock must initially be held.
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*
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* Returns either number of pages pinned (which may be less than the
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* number requested), or an error. Details about the return value:
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*
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* -- If nr_pages is 0, returns 0.
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* -- If nr_pages is >0, but no pages were pinned, returns -errno.
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* -- If nr_pages is >0, and some pages were pinned, returns the number of
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* pages pinned. Again, this may be less than nr_pages.
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*
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* The caller is responsible for releasing returned @pages, via put_page().
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*
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* @vmas are valid only as long as mmap_sem is held.
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*
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* Must be called with mmap_sem held for read or write.
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*
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* get_user_pages walks a process's page tables and takes a reference to
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* each struct page that each user address corresponds to at a given
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* instant. That is, it takes the page that would be accessed if a user
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* thread accesses the given user virtual address at that instant.
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*
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* This does not guarantee that the page exists in the user mappings when
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* get_user_pages returns, and there may even be a completely different
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* page there in some cases (eg. if mmapped pagecache has been invalidated
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* and subsequently re faulted). However it does guarantee that the page
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* won't be freed completely. And mostly callers simply care that the page
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* contains data that was valid *at some point in time*. Typically, an IO
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* or similar operation cannot guarantee anything stronger anyway because
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* locks can't be held over the syscall boundary.
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*
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* If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
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* is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
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* be called after the page is finished with, and before put_page is called.
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*
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* get_user_pages is typically used for fewer-copy IO operations, to get a
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* handle on the memory by some means other than accesses via the user virtual
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* addresses. The pages may be submitted for DMA to devices or accessed via
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* their kernel linear mapping (via the kmap APIs). Care should be taken to
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* use the correct cache flushing APIs.
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*
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* See also get_user_pages_fast, for performance critical applications.
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*
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* get_user_pages should be phased out in favor of
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* get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
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* should use get_user_pages because it cannot pass
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* FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
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*/
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long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
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unsigned long start, unsigned long nr_pages,
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unsigned int gup_flags, struct page **pages,
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struct vm_area_struct **vmas, int *locked)
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{
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/*
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* FIXME: Current FOLL_LONGTERM behavior is incompatible with
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* FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
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* vmas. As there are no users of this flag in this call we simply
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* disallow this option for now.
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*/
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if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
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return -EINVAL;
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return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
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locked,
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gup_flags | FOLL_TOUCH | FOLL_REMOTE);
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}
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EXPORT_SYMBOL(get_user_pages_remote);
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/**
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* populate_vma_page_range() - populate a range of pages in the vma.
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* @vma: target vma
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@ -1626,6 +1544,98 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
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}
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#endif /* CONFIG_FS_DAX || CONFIG_CMA */
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/*
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* get_user_pages_remote() - pin user pages in memory
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* @tsk: the task_struct to use for page fault accounting, or
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* NULL if faults are not to be recorded.
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* @mm: mm_struct of target mm
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* @start: starting user address
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* @nr_pages: number of pages from start to pin
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* @gup_flags: flags modifying lookup behaviour
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long. Or NULL, if caller
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* only intends to ensure the pages are faulted in.
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* @vmas: array of pointers to vmas corresponding to each page.
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* Or NULL if the caller does not require them.
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* @locked: pointer to lock flag indicating whether lock is held and
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* subsequently whether VM_FAULT_RETRY functionality can be
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* utilised. Lock must initially be held.
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*
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* Returns either number of pages pinned (which may be less than the
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* number requested), or an error. Details about the return value:
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*
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* -- If nr_pages is 0, returns 0.
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* -- If nr_pages is >0, but no pages were pinned, returns -errno.
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* -- If nr_pages is >0, and some pages were pinned, returns the number of
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* pages pinned. Again, this may be less than nr_pages.
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*
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* The caller is responsible for releasing returned @pages, via put_page().
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*
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* @vmas are valid only as long as mmap_sem is held.
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*
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* Must be called with mmap_sem held for read or write.
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*
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* get_user_pages walks a process's page tables and takes a reference to
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* each struct page that each user address corresponds to at a given
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* instant. That is, it takes the page that would be accessed if a user
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* thread accesses the given user virtual address at that instant.
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*
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* This does not guarantee that the page exists in the user mappings when
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* get_user_pages returns, and there may even be a completely different
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* page there in some cases (eg. if mmapped pagecache has been invalidated
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* and subsequently re faulted). However it does guarantee that the page
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* won't be freed completely. And mostly callers simply care that the page
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* contains data that was valid *at some point in time*. Typically, an IO
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* or similar operation cannot guarantee anything stronger anyway because
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* locks can't be held over the syscall boundary.
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*
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* If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
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* is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
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* be called after the page is finished with, and before put_page is called.
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*
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* get_user_pages is typically used for fewer-copy IO operations, to get a
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* handle on the memory by some means other than accesses via the user virtual
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* addresses. The pages may be submitted for DMA to devices or accessed via
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* their kernel linear mapping (via the kmap APIs). Care should be taken to
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* use the correct cache flushing APIs.
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*
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* See also get_user_pages_fast, for performance critical applications.
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*
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* get_user_pages should be phased out in favor of
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* get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
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* should use get_user_pages because it cannot pass
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* FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
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*/
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long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
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unsigned long start, unsigned long nr_pages,
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unsigned int gup_flags, struct page **pages,
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struct vm_area_struct **vmas, int *locked)
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{
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/*
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* Parts of FOLL_LONGTERM behavior are incompatible with
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* FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
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* vmas. However, this only comes up if locked is set, and there are
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* callers that do request FOLL_LONGTERM, but do not set locked. So,
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* allow what we can.
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*/
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if (gup_flags & FOLL_LONGTERM) {
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if (WARN_ON_ONCE(locked))
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return -EINVAL;
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/*
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* This will check the vmas (even if our vmas arg is NULL)
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* and return -ENOTSUPP if DAX isn't allowed in this case:
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*/
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return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
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vmas, gup_flags | FOLL_TOUCH |
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FOLL_REMOTE);
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}
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return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
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locked,
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gup_flags | FOLL_TOUCH | FOLL_REMOTE);
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}
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EXPORT_SYMBOL(get_user_pages_remote);
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/*
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* This is the same as get_user_pages_remote(), just with a
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* less-flexible calling convention where we assume that the task
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