insufficient TLB flush for x86 PV guests in shadow mode For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. To address XSA-401, code was moved inside a function in Xen. This code movement missed a variable changing meaning / value between old and new code positions. The now wrong use of the variable did lead to a wrong TLB flush condition, omitting flushes where such are necessary.
https://xenbits.xenproject.org/xsa/advisory-408.txt
https://www.debian.org/security/2022/dsa-5272
http://xenbits.xen.org/xsa/advisory-408.html