[Xenomai] Eager FPU vs. recent kernels

Henning Schild henning.schild at siemens.com
Fri Jul 13 14:37:32 CEST 2018


Am Mon, 9 Jul 2018 19:48:28 +0200
schrieb Jan Kiszka <jan.kiszka at siemens.com>:

> 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).

I have just reached that point in the 4.14 x86 work. And from what i
can see right now is that it would be a good idea to look into the FPU
thing independent of 4.14. So i will start working on that for 4.9 and
probably 4.4 to understand what 4.14 needs.

Henning

> 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
> 




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