Re: [Minios-devel] [UNIKRAFT RFC PATCH 2/5] plat/kvm: arm64: Enable the fp/simd at the starting point

[Julien Grall <julien@xxxxxxx>]

On 20/12/2019 08:04, Santiago Pagani wrote:

Hi,

May I ask to avoid top-posting? This makes the conversation fairly 
difficult to read.
> Actually, the comment is wrong. Setting those two bits in cpacr_el1 does not 
> enable fp/simd, but actually disables traps for floating point and SIMD 
> instructions both in EL0 and EL1.
> The actually enabling of floating point and SIMD instructions is done by your 
> other patch that removes the -mgeneral-regs-only flag.
> Therefore, there is no harm in doing that in the kernel when floating point is 
> enabled. I would however fix the comment though.
Not quite, you make your life so much more difficult if your kernel 
should not use FPSIMD registers and will use them (see my other answer).
So for safety, it is better to keep trapping FPSIMD if they are not 
meant to be used. This is likely to avoid you a lot of debugging in the 
future if FPSIMD are misused.
Cheers,

--
Julien Grall

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