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