Description: Rogue backends can cause DoS of guests via high frequency events (hvc_xen (console))
References:
 https://xenbits.xen.org/xsa/advisory-391.html
 https://xenbits.xen.org/xsa/xsa391-linux-3.patch
Notes:
 carnil> For 5.15.y fixed as well in 5.15.11.
Bugs:
upstream: released (5.16-rc7) [fe415186b43df0db1f17fa3a46275fd92107fe71]
5.10-upstream-stable: released (5.10.88) [8fa3a370cc2af858a9ba662ca4f2bd0917550563]
4.19-upstream-stable: released (4.19.222) [57e46acb3b48ea4e8efb1e1bea2e89e0c6cc43e2]
4.9-upstream-stable: released (4.9.294) [728389c21176b2095fa58e858d5ef1d2f2aac429]
sid: released (5.15.15-1)
5.10-bullseye-security: released (5.10.92-1)
4.19-buster-security: released (4.19.232-1)
4.9-stretch-security: released (4.9.303-1)