[Xenomai] Eager FPU vs. recent kernels

Jan Kiszka jan.kiszka at siemens.com
Mon Jul 9 19:48:28 CEST 2018


Hi,

the x86 FPU changes that so far only affected 4.14 and delayed its ipipe
progress on that arch. However, CVE-2018-3665 is not making it a topic
for every ipipe kernel (that should be kept up to date): lazy FPU is
history, now also for security reasons (before that only for performance
reasons).

That raises the question how much the Xenomai 3 core depends on lazy FPU
state switching. Philippe, can you describe the general flow of context
switching /wrt the FPU state so far? Can we overcome lazy by just
replacing the current FPU functions in kernel/cobalt/arch/x86/thread.c
with eager ones, maybe depending on some CONFIG_IPIPE_X86_HAS_EAGER_FPU
compile-time dependency?

Thanks,
Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux



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