Re: [PATCH v2 3/6] RISC-V: Check scalar unaligned access on all CPUs

[Conor Dooley]

On Thu, Jun 13, 2024 at 03:16:12PM -0400, Jesse Taube wrote:
> Originally, the check_unaligned_access_emulated_all_cpus function
> only checked the boot hart. This fixes the function to check all
> harts.

This seems like it should be split out and get a Fixes: tag & a cc:
stable.

> Check for Zicclsm before checking for unaligned access. This will
> greatly reduce the boot up time as finding the access speed is no longer
> necessary.
> 
> Signed-off-by: Jesse Taube <jesse@xxxxxxxxxxxx>
> ---
> V1 -> V2:
>  - New patch
> ---
>  arch/riscv/kernel/traps_misaligned.c       | 23 ++++++----------------
>  arch/riscv/kernel/unaligned_access_speed.c | 23 +++++++++++++---------
>  2 files changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index b62d5a2f4541..8fadbe00dd62 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -526,31 +526,17 @@ int handle_misaligned_store(struct pt_regs *regs)
>  	return 0;
>  }
>  
> -static bool check_unaligned_access_emulated(int cpu)
> +static void check_unaligned_access_emulated(struct work_struct *unused)
>  {
> +	int cpu = smp_processor_id();
>  	long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
>  	unsigned long tmp_var, tmp_val;
> -	bool misaligned_emu_detected;
>  
>  	*mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
>  
>  	__asm__ __volatile__ (
>  		"       "REG_L" %[tmp], 1(%[ptr])\n"
>  		: [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory");
> -
> -	misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED);
> -	/*
> -	 * If unaligned_ctl is already set, this means that we detected that all
> -	 * CPUS uses emulated misaligned access at boot time. If that changed
> -	 * when hotplugging the new cpu, this is something we don't handle.
> -	 */
> -	if (unlikely(unaligned_ctl && !misaligned_emu_detected)) {
> -		pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n");
> -		while (true)
> -			cpu_relax();
> -	}
> -
> -	return misaligned_emu_detected;
>  }
>  
>  bool check_unaligned_access_emulated_all_cpus(void)
> @@ -562,8 +548,11 @@ bool check_unaligned_access_emulated_all_cpus(void)
>  	 * accesses emulated since tasks requesting such control can run on any
>  	 * CPU.
>  	 */
> +	schedule_on_each_cpu(check_unaligned_access_emulated);
> +
>  	for_each_online_cpu(cpu)
> -		if (!check_unaligned_access_emulated(cpu))
> +		if (per_cpu(misaligned_access_speed, cpu)
> +		    != RISCV_HWPROBE_MISALIGNED_EMULATED)
>  			return false;
>  
>  	unaligned_ctl = true;
> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> index a9a6bcb02acf..70c1588fc353 100644
> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c
> @@ -259,23 +259,28 @@ static int check_unaligned_access_speed_all_cpus(void)
>  	kfree(bufs);
>  	return 0;
>  }
> +#endif /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
>  
>  static int check_unaligned_access_all_cpus(void)
>  {
> -	bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> +	bool all_cpus_emulated;
> +	int cpu;
>  
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICCLSM)) {
> +		for_each_online_cpu(cpu) {
> +			per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
> +		}
> +		return 0;
> +	}
> +
> +	all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> +
> +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS

Can we make this an IS_ENABLED() please?


Thanks,
Conor.

>  	if (!all_cpus_emulated)
>  		return check_unaligned_access_speed_all_cpus();
> +#endif
>  
>  	return 0;
>  }
> -#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> -static int check_unaligned_access_all_cpus(void)
> -{
> -	check_unaligned_access_emulated_all_cpus();
> -
> -	return 0;
> -}
> -#endif
>  
>  arch_initcall(check_unaligned_access_all_cpus);
> -- 
> 2.43.0
>

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