linux-kernel - Re: [PATCH v3 2/3] arch/arm64: fpsimd: Introduce fpsimd_save_and_flush_cpu

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Date:   Wed, 24 Apr 2019 14:17:20 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        ard.biesheuvel@...aro.org, julien.thierry@....com,
        marc.zyngier@....com, catalin.marinas@....com,
        suzuki.poulose@....com, will.deacon@....com,
        christoffer.dall@....com, james.morse@....com
Subject: Re: [PATCH v3 2/3] arch/arm64: fpsimd: Introduce
 fpsimd_save_and_flush_cpu_state() and use it

On Tue, Apr 23, 2019 at 02:57:18PM +0100, Julien Grall wrote:
> tent-Length: 4295
> Lines: 128
> 
> The only external user of fpsimd_save() and fpsimd_flush_cpu_state() is
> the KVM FPSIMD code.
> 
> A following patch will introduce a mechanism to acquire owernship of the
> FPSIMD/SVE context for performing context management operations. Rather
> than having to export the new helpers to get/put the context, we can just
> introduce a new function to combine fpsimd_save() and
> fpsimd_flush_cpu_state().
> 
> This has also the advantage to remove any external call of fpsimd_save()
> and fpsimd_flush_cpu_state(), so they can be turned static.
> 
> Lastly, the new function can also be used in the PM notifier.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> 
> ---
>     kernel_neon_begin() does not use fpsimd_save_and_flush_cpu_state()
>     because the next patch will modify the function to also grab the
>     FPSIMD/SVE context.
> 
>     Changes in v3:
>         - Rework the commit message
>         - Move the prototype of fpsimd_save_and_flush_cpu_state()
>         further down in the header
>         - Remove comment in kvm_arch_vcpu_put_fp()
> 
>     Changes in v2:
>         - Patch added
> ---
>  arch/arm64/include/asm/fpsimd.h |  5 ++---
>  arch/arm64/kernel/fpsimd.c      | 17 +++++++++++++----
>  arch/arm64/kvm/fpsimd.c         |  4 +---
>  3 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
> index b73d12fcc7f9..c311d36ecffe 100644
> --- a/arch/arm64/include/asm/fpsimd.h
> +++ b/arch/arm64/include/asm/fpsimd.h
> @@ -48,8 +48,6 @@ struct task_struct;
>  extern void fpsimd_save_state(struct user_fpsimd_state *state);
>  extern void fpsimd_load_state(struct user_fpsimd_state *state);
>  
> -extern void fpsimd_save(void);
> -
>  extern void fpsimd_thread_switch(struct task_struct *next);
>  extern void fpsimd_flush_thread(void);
>  
> @@ -63,7 +61,8 @@ extern void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *state,
>  				     void *sve_state, unsigned int sve_vl);
>  
>  extern void fpsimd_flush_task_state(struct task_struct *target);
> -extern void fpsimd_flush_cpu_state(void);
> +
> +extern void fpsimd_save_and_flush_cpu_state(void);

Nit: You could drop this blank line: these are all "state maintenance"
operations, roughly speaking.

But don't bother unless you respin for some other reason.

[...]

With or without that,

Reviewed-by: Dave Martin <Dave.Martin@....com>

Cheers
---Dave