mm: handle read faults under the VMA lock

Most file-backed faults are already handled through ->map_pages(), but if
we need to do I/O we'll come this way.  Since filemap_fault() is now safe
to be called under the VMA lock, we can handle these faults under the VMA
lock now.

Link: https://lkml.kernel.org/r/20231006195318.4087158-6-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -4617,10 +4617,9 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
 			return ret;
 	}
 
-	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
-		vma_end_read(vmf->vma);
-		return VM_FAULT_RETRY;
-	}
+	ret = vmf_can_call_fault(vmf);
+	if (ret)
+		return ret;
 
 	ret = __do_fault(vmf);
 	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))