CVE-2021-47450

In the Linux kernel, the following vulnerability has been resolved: KVM:
arm64: Fix host stage-2 PGD refcount The KVM page-table library refcounts
the pages of concatenated stage-2 PGDs individually. However, when running
KVM in protected mode, the host’s stage-2 PGD is currently managed by EL2
as a single high-order compound page, which can cause the refcount of the
tail pages to reach 0 when they shouldn’t, hence corrupting the page-table.
Fix this by introducing a new hyp_split_page() helper in the EL2 page
allocator (matching the kernel’s split_page() function), and make use of it
from host_s2_zalloc_pages_exact().