A bug in AMD CPU’s core logic may allow for an attacker, using specific code from an unprivileged VM, to trigger a CPU core hang resulting in a potential denial of service. AMD believes the specific code includes a specific x86 instruction sequence that would not be generated by compilers.
https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1028
https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1027