The workaround for XSA-433 (Zenbleed, CVE-2023-20593) was later
re-worked to better integrate with other manipulations of the same MSR.
In this rework an inverted conditional was introduced, resulting in the
workaround to not be applied when needed and vice versa.
For more details, see:
http://xenbits.xen.org/xsa/advisory-433.html
