FAULT_FLAG_VMA_LOCK flag was introduced without proper description. Fix
this by documenting it.
Fixes: 863be34fc093 ("mm: add FAULT_FLAG_VMA_LOCK flag")
Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20230301113648.7c279865@xxxxxxxxxxxxxxxx/
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
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Fix cleanly apply over mm-unstable, SHA in "Fixes" is from that tree.