Subject: Re: [PATCH v3 6/8] arm64/sve: Implement a helper to load SVE registers from FPSIMD state

From: Dave Martin <[email-masked]>
Date: Wed, 15 Jul 2020 17:52:19 +0100

On Mon, Jun 29, 2020 at 02:35:54PM +0100, Mark Brown wrote:
> From: Julien Grall <[email-masked]>
> 
> In a follow-up patch, we may save the FPSIMD rather than the full SVE
> state when the state has to be zeroed on return to userspace (e.g
> during a syscall).
> 
> Introduce an helper to load SVE vectors from FPSIMD state and zero the rest
> of SVE registers.
> 
> Signed-off-by: Julien Grall <[email-masked]>
> Reviewed-by: Dave Martin <[email-masked]>
> Signed-off-by: Mark Brown <[email-masked]>
> ---
>  arch/arm64/include/asm/fpsimd.h  |  2 ++
>  arch/arm64/kernel/entry-fpsimd.S | 17 +++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
> index 958f642e930d..bec5f14b622a 100644
> --- a/arch/arm64/include/asm/fpsimd.h
> +++ b/arch/arm64/include/asm/fpsimd.h
> @@ -70,6 +70,8 @@ extern void sve_save_state(void *state, u32 *pfpsr);
>  extern void sve_load_state(void const *state, u32 const *pfpsr,
>  			   unsigned long vq_minus_1);
>  extern void sve_flush_live(void);
> +extern void sve_load_from_fpsimd_state(struct user_fpsimd_state const *state,
> +				       unsigned long vq_minus_1);
>  extern unsigned int sve_get_vl(void);
>  
>  struct arm64_cpu_capabilities;
> diff --git a/arch/arm64/kernel/entry-fpsimd.S b/arch/arm64/kernel/entry-fpsimd.S
> index fdf7a5a35c63..5b1a9adfb00b 100644
> --- a/arch/arm64/kernel/entry-fpsimd.S
> +++ b/arch/arm64/kernel/entry-fpsimd.S
> @@ -48,6 +48,23 @@ SYM_FUNC_START(sve_get_vl)
>  	ret
>  SYM_FUNC_END(sve_get_vl)
>  
> +/*
> + * Load SVE state from FPSIMD state.
> + *
> + * x0 = pointer to struct fpsimd_state
> + * x1 = VQ - 1
> + *
> + * Each SVE vector will be loaded with the first 128-bits taken from FPSIMD
> + * and the rest zeroed. All the other SVE registers will be zeroed.
> + */
> +SYM_FUNC_START(sve_load_from_fpsimd_state)
> +		sve_load_vq	x1, x2, x3
> +		fpsimd_restore	x0, 8
> + _for n, 0, 15, _sve_pfalse	\n
> +		_sve_wrffr 0

FWIW, trivial nit that I guess I didn't spot previously:
tab before 0 here?

Mind you, the spacing is already a bit off in this file.

Cheers
---Dave

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