Re: [RFT PATCH v1 2/7] arm64: restore FPSIMD to default state for kernel and signal contexts

[Catalin Marinas]

On Fri, Sep 27, 2013 at 09:04:42AM +0100, Jiang Liu wrote:
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index bb785d2..12a25e5 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -80,9 +80,14 @@ void fpsimd_thread_switch(struct task_struct *next)
>  
>  void fpsimd_flush_thread(void)
>  {
> +     struct fpsimd_state *state = &current->thread.fpsimd_state;
> +
>       preempt_disable();
> -     memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
> -     fpsimd_load_state(&current->thread.fpsimd_state);
> +     memset(state, 0, sizeof(struct fpsimd_state));
> +#if (AARCH64_FPCR_DEFAULT_VAL != 0)
> +     state->fpcr = AARCH64_FPCR_DEFAULT_VAL;
> +#endif
> +     fpsimd_load_state(state);
>       preempt_enable();

We can leave this to 0 as the default for user. Glibc already programs
this register.

>  }
>  
> @@ -99,6 +104,8 @@ void kernel_neon_begin(void)
>  
>       if (current->mm)
>               fpsimd_save_state(&current->thread.fpsimd_state);
> +
> +     fpsimd_init_hw_state();

This function should indeed do some initialisation rather than relying
on whatever the user set for FPCR.

> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 890a591..6d80612 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -52,6 +52,7 @@ static int preserve_fpsimd_context(struct fpsimd_context 
> __user *ctx)
>  
>       /* dump the hardware registers to the fpsimd_state structure */
>       fpsimd_save_state(fpsimd);
> +     fpsimd_init_hw_state();

Here I think we need to leave the default user setting for fpcr as
decided by glibc (or libgcc) when an application starts.

>       /* copy the FP and status/control registers */
>       err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));
> diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
> index e393174..cb2cb41 100644
> --- a/arch/arm64/kernel/signal32.c
> +++ b/arch/arm64/kernel/signal32.c
> @@ -248,6 +248,7 @@ static int compat_preserve_vfp_context(struct 
> compat_vfp_sigframe __user *frame)
>        * in AArch32.
>        */
>       fpsimd_save_state(fpsimd);
> +     fpsimd_init_hw_state();

Same here.

-- 
Catalin
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