617a11eab6
The explanation from https://reviews.freebsd.org/D39637 by stevek: The "use_xsave" variable is a global and that is only supposed to be initialized early before scheduling gets started. However, with the way the ifuncs for "fpusave" and "fpurestore" are implemented, the value could be changed at runtime when scheduling is active if "use_xsave" was set to 0 by the tunable. This leaves a window of opportunity where "use_xsave" gets re-initialized to 1 and a context switch could occur with a thread that was not set up to be able to use xsave functionality. This can lead to an "privileged instruction fault". The fix is to protect "use_xsave" from being initialized more than once. Reported and reviewed by: stevek Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D39660 |
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