linux-kernel - Re: [PATCH v4 3/7] RISC-V: Check scalar unaligned access on all CPUs

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Message-ID: <ZpBe8ECHxJ9QXVB2@ghost>
Date: Thu, 11 Jul 2024 15:38:40 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Jesse Taube <jesse@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Conor Dooley <conor@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Clément Léger <cleger@...osinc.com>,
	Evan Green <evan@...osinc.com>,
	Andrew Jones <ajones@...tanamicro.com>,
	Xiao Wang <xiao.w.wang@...el.com>, Andy Chiu <andy.chiu@...ive.com>,
	Eric Biggers <ebiggers@...gle.com>,
	Greentime Hu <greentime.hu@...ive.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Costa Shulyupin <costa.shul@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Anup Patel <apatel@...tanamicro.com>,
	Zong Li <zong.li@...ive.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Erick Archer <erick.archer@....com>,
	Joel Granados <j.granados@...sung.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v4 3/7] RISC-V: Check scalar unaligned access on all CPUs

On Thu, Jul 11, 2024 at 05:58:42PM -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.
> 
> Fixes: 71c54b3d169d ("riscv: report misaligned accesses emulation to hwprobe")
> Signed-off-by: Jesse Taube <jesse@...osinc.com>
> Cc: stable@...r.kernel.org
> ---
> V1 -> V2:
>  - New patch
> V2 -> V3:
>  - Split patch
> V3 -> V4:
>  - Re-add check for a system where a heterogeneous
>     CPU is hotplugged into a previously homogenous
>     system.
> ---
>  arch/riscv/kernel/traps_misaligned.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index b62d5a2f4541..1a1bb41472ea 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -526,11 +526,11 @@ 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)

Small change, can you give this a different name like "work" and instead
give it the attribute "__always_unused" like:

struct work_struct *work __always_unused

Otherwise,

Reviewed-by: Charlie Jenkins <charlie@...osinc.com>

>  {
> +	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;
>  
> @@ -538,19 +538,16 @@ static bool check_unaligned_access_emulated(int cpu)
>  		"       "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)) {
> +	if (unlikely(unaligned_ctl && (*mas_ptr != RISCV_HWPROBE_MISALIGNED_EMULATED))) {
>  		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 +559,11 @@ 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;
> -- 
> 2.45.2
>