Re: [Minios-devel] [UNIKRAFT PATCH v3 3/7] plat/kvm: arm64: Enable the fp/simd at the starting point

[Sharan Santhanam <sharan.santhanam@xxxxxxxxx>]

On 4/2/20 6:18 AM, Jia He wrote:
> Write the sys reg to enable the fp/simd feature, otherwise it will
> cause floating point/simd exception when touching q0-q31.
>
> Signed-off-by: Jia He <justin.he@xxxxxxx>
> ---
>   plat/kvm/arm/entry64.S | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/plat/kvm/arm/entry64.S b/plat/kvm/arm/entry64.S
> index 359a310..1e32268 100644
> --- a/plat/kvm/arm/entry64.S
> +++ b/plat/kvm/arm/entry64.S
> @@ -36,6 +36,7 @@
>   #include <kvm-arm/mm.h>
>   #include <arm/cpu_defs.h>
>   #include <uk/plat/common/sections.h>
> +#include <uk/config.h>
>   
>   .global page_table_size
>   .data
> @@ -49,6 +50,13 @@ page_table_size:
>   
>   .text
>   ENTRY(_libkvmplat_entry)
> +#ifdef CONFIG_FLOAT_POINT
> +       /* Enable fp/simd support */
> +       ldr        x0, =(3 << 20)
> +       msr        cpacr_el1, x0
> +       isb
> +#endif
Do we need to enable the floating point upon entry?

It might be better to do it at the setup phase in `setup.c` and 
implement this as inline assembly
Since it is a cpu feature, it might be better to provide functions to 
enable and disable it.
> +
>         /* Calculate the image size */
>         ldr x25, =_dtb
>         ldr x26, =_end
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