Re: [PATCH v7 09/14] riscv: misaligned: move emulated access uniformity check in a function

From: "Clément Léger" <cleger@rivosinc.com>
To: Charlie Jenkins <charlie@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Anup Patel <anup@brainfault.org>,
	Atish Patra <atishp@atishpatra.org>,
	Shuah Khan <shuah@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, kvm@vger.kernel.org,
	kvm-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org,
	Samuel Holland <samuel.holland@sifive.com>,
	Andrew Jones <ajones@ventanamicro.com>,
	Deepak Gupta <debug@rivosinc.com>
Subject: Re: [PATCH v7 09/14] riscv: misaligned: move emulated access uniformity check in a function
Date: Tue, 20 May 2025 10:19:47 +0200	[thread overview]
Message-ID: <126762fc-17ca-4e9d-94d0-3aed1ae321ff@rivosinc.com> (raw)
In-Reply-To: <aCu_ce-kVQsyjrh5@ghost>

On 20/05/2025 01:32, Charlie Jenkins wrote:
> On Thu, May 15, 2025 at 10:22:10AM +0200, Clément Léger wrote:
>> Split the code that check for the uniformity of misaligned accesses
>> performance on all cpus from check_unaligned_access_emulated_all_cpus()
>> to its own function which will be used for delegation check. No
>> functional changes intended.
>>
>> Signed-off-by: Clément Léger <cleger@rivosinc.com>
>> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
>> ---
>>  arch/riscv/kernel/traps_misaligned.c | 20 ++++++++++++++------
>>  1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
>> index e551ba17f557..287ec37021c8 100644
>> --- a/arch/riscv/kernel/traps_misaligned.c
>> +++ b/arch/riscv/kernel/traps_misaligned.c
>> @@ -647,6 +647,18 @@ bool __init check_vector_unaligned_access_emulated_all_cpus(void)
>>  }
>>  #endif
>>  
>> +static bool all_cpus_unaligned_scalar_access_emulated(void)
>> +{
>> +	int cpu;
>> +
>> +	for_each_online_cpu(cpu)
>> +		if (per_cpu(misaligned_access_speed, cpu) !=
> 
> misaligned_access_speed is only defined when
> CONFIG_RISCV_SCALAR_MISALIGNED. This function should return false when
> !CONFIG_RISCV_SCALAR_MISALIGNED and only use this logic otherwise.

Hi Charlie,

misaligned_access_speed is defined in unaligned_access_speed.c which is
compiled based on CONFIG_RISCV_MISALIGNED (ditto for trap_misaligned.c)

obj-$(CONFIG_RISCV_MISALIGNED)	+= unaligned_access_speed.o

However, the declaration for it in the header cpu-feature.h however is
under a CONFIG_RISCV_SCALAR_MISALIGNED ifdef. So either the declaration
or the definition is wrong but the ifdefery soup makes it quite
difficult to understand what's going on.

I would suggest to move the DECLARE_PER_CPU under
CONFIG_RISCV_MISALIGNED so that it reduces ifdef in traps_misaligned as
well.

Thanks,

Clément

> 
> - Charlie
> 
>> +		    RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED)
>> +			return false;
>> +
>> +	return true;
>> +}
>> +
>>  #ifdef CONFIG_RISCV_SCALAR_MISALIGNED
>>  
>>  static bool unaligned_ctl __read_mostly;
>> @@ -685,8 +697,6 @@ static int cpu_online_check_unaligned_access_emulated(unsigned int cpu)
>>  
>>  bool __init check_unaligned_access_emulated_all_cpus(void)
>>  {
>> -	int cpu;
>> -
>>  	/*
>>  	 * We can only support PR_UNALIGN controls if all CPUs have misaligned
>>  	 * accesses emulated since tasks requesting such control can run on any
>> @@ -694,10 +704,8 @@ bool __init check_unaligned_access_emulated_all_cpus(void)
>>  	 */
>>  	on_each_cpu(check_unaligned_access_emulated, NULL, 1);
>>  
>> -	for_each_online_cpu(cpu)
>> -		if (per_cpu(misaligned_access_speed, cpu)
>> -		    != RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED)
>> -			return false;
>> +	if (!all_cpus_unaligned_scalar_access_emulated())
>> +		return false;
>>  
>>  	unaligned_ctl = true;
>>  	return true;
>> -- 
>> 2.49.0
>>
>>
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