Describe CVE-2021-47567.
What is CVE-2021-47567?
In the Linux kernel, the following vulnerability has been resolved:

powerpc/32: Fix hardlockup on vmap stack overflow

Since the commit c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not
activate MMU before reading task struct") a vmap stack overflow
results in a hard lockup. This is because emergency_ctx is still
addressed with its virtual address allthough data MMU is not active
anymore at that time.

Fix it by using a physical address instead..