linux-kernel - Re: [PATCH v3 3/8] RISC-V: Check scalar unaligned access on all CPUs

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Message-ID: <ed410b0f-0062-4fbb-97e0-86fd492fb5ca@rivosinc.com>
Date: Thu, 11 Jul 2024 16:25:01 -0400
From: Jesse Taube <jesse@...osinc.com>
To: Evan Green <evan@...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>, Andrew Jones <ajones@...tanamicro.com>,
 Charlie Jenkins <charlie@...osinc.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 v3 3/8] RISC-V: Check scalar unaligned access on all CPUs

On 7/10/24 11:55, Evan Green wrote:
> On Mon, Jun 24, 2024 at 5:51 PM Jesse Taube <jesse@...osinc.com> 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
>> ---
>>   arch/riscv/kernel/traps_misaligned.c | 23 ++++++-----------------
>>   1 file changed, 6 insertions(+), 17 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();
>> -       }
> 
> This chunk was meant to detect and refuse to run on a system where a
> heterogeneous CPU is hotplugged into a previously homogenous system.
> The commit message doesn't mention this change, how come you
> deleted it?

Sorry for the long wait.
I do not remember why I removed this.
Your right it shouldn't be removed, I added it back.

Thanks,
Jesse Taube
> 
> 
>> -
>> -       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;
>> --
>> 2.45.2
>>