CVE-2021-47491

In the Linux kernel, the following vulnerability has been resolved: mm:
khugepaged: skip huge page collapse for special files The read-only THP for
filesystems will collapse THP for files opened readonly and mapped with
VM_EXEC. The intended usecase is to avoid TLB misses for large text
segments. But it doesn’t restrict the file types so a THP could be
collapsed for a non-regular file, for example, block device, if it is
opened readonly and mapped with EXEC permission. This may cause bugs, like
[1] and [2]. This is definitely not the intended usecase, so just collapse
THP for regular files in order to close the attack surface.
[[email protected]: fix vm_file check [3]]