[PATCH v4] arm64: errata: Fix exec handling in erratum 1418040 workaround

[D Scott Phillips]

D Scott Phillips <scott at os.amperecomputing.com> writes:

> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index aacf2f5559a8..b37ff23e625e 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -439,34 +439,23 @@ static void entry_task_switch(struct task_struct *next)
>  
>  /*
>   * ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT.
> - * Assuming the virtual counter is enabled at the beginning of times:
> - *
> - * - disable access when switching from a 64bit task to a 32bit task
> - * - enable access when switching from a 32bit task to a 64bit task
> + * Ensure access is disabled when switching to a 32bit task, ensure
> + * access is enabled when switching to a 64bit task.
>   */
> -static void erratum_1418040_thread_switch(struct task_struct *prev,
> -					  struct task_struct *next)
> +static void erratum_1418040_thread_switch(struct task_struct *next)
>  {
> -	bool prev32, next32;
> -	u64 val;
> -
> -	if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040))
> -		return;
> +	preempt_disable();
>  
> -	prev32 = is_compat_thread(task_thread_info(prev));
> -	next32 = is_compat_thread(task_thread_info(next));
> -
> -	if (prev32 == next32 || !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
> +	if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) ||
> +	    !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
>  		return;

Oops, missing preempt_enable() here.