mm/gup: remove vmas parameter from get_user_pages_remote()

The only instances of get_user_pages_remote() invocations which used the
vmas parameter were for a single page which can instead simply look up the
VMA directly. In particular:-

- __update_ref_ctr() looked up the VMA but did nothing with it so we simply
  remove it.

- __access_remote_vm() was already using vma_lookup() when the original
  lookup failed so by doing the lookup directly this also de-duplicates the
  code.

We are able to perform these VMA operations as we already hold the
mmap_lock in order to be able to call get_user_pages_remote().

As part of this work we add get_user_page_vma_remote() which abstracts the
VMA lookup, error handling and decrementing the page reference count should
the VMA lookup fail.

This forms part of a broader set of patches intended to eliminate the vmas
parameter altogether.

[[email protected]: avoid passing NULL to PTR_ERR]
Link: https://lkml.kernel.org/r/d20128c849ecdbf4dd01cc828fcec32127ed939a.1684350871.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]> (for arm64)
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Janosch Frank <[email protected]> (for s390)
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Christian König <[email protected]>
Cc: Dennis Dalessandro <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Sakari Ailus <[email protected]>
Cc: Sean Christopherson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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