Linux hasn’t used CR0.TS for some time. I removed it a while back because manipulating TS is very very slow.
(I am not part of any process with respect to this, embargoed or otherwise.)
Edit: the upstream commit is 58122bf1d856a4ea9581d62a07c557d997d46a19, called “x86/fpu: Default eagerfpu=on on all CPUs”, and it landed in early 2016. Greg K-H just submitted backports to all older supported kernels.
AFAIK the entire idea dates back to the days of the 80286/80287 (and 80386/80387) when accessing the coprocessor was slow, and a TSS switch (Linux used it until the late 1990s) set that bit for you.
That commit disables the lazy mode by default on processors supporting the XSAVEOPT instruction. But, it's possible to override that default with the eagerfpu= kernel command-line option, or that a hypervisor has masked out support for that instruction even on hardware with XSAVEOPT support.
The point is: although relatively unlikely, it is still _possible_ that you need some mitigation even if you have newer hardware (Sandybridge or newer is where XSAVEOPT first showed up, I believe).
(I am not part of any process with respect to this, embargoed or otherwise.)
Edit: the upstream commit is 58122bf1d856a4ea9581d62a07c557d997d46a19, called “x86/fpu: Default eagerfpu=on on all CPUs”, and it landed in early 2016. Greg K-H just submitted backports to all older supported kernels.