Most likely you have the mitigation already in place, that is disabeling the XTheadVector extension.
The regular distributions don't enable it, since it's a non standard incompatible vendor extension based on a draft spec.
When I wanted to benchmark their implementation last year I patched a kernel to enable it, and needed to consult the open source part of the core [0] to figure out that they placed the enable CSR bit in a different location than the final ratified spec. [1]
> No, software updates or patches cannot fix this vulnerability because it is a hardware bug. The only mitigation is to disable the vector extension in the CPU, which unfortunately impacts the CPU’s performance.
When I wanted to benchmark their implementation last year I patched a kernel to enable it, and needed to consult the open source part of the core [0] to figure out that they placed the enable CSR bit in a different location than the final ratified spec. [1]
[0] https://github.com/T-head-Semi/openc906 (doesn't include XTheadVector extension)
[1] https://github.com/camel-cdr/rvv-d1