linux-kernel - Re: [PATCH -fixes v3 1/2] riscv: Fix enabling cbo.zero when running in M-mode

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Date: Tue, 27 Feb 2024 20:48:54 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Andrew Jones <ajones@...tanamicro.com>,
 Samuel Holland <samuel.holland@...ive.com>
Cc: Palmer Dabbelt <palmer@...belt.com>, linux-kernel@...r.kernel.org,
 Conor Dooley <conor@...nel.org>, linux-riscv@...ts.infradead.org,
 Stefan O'Rear <sorear@...tmail.com>, stable@...r.kernel.org
Subject: Re: [PATCH -fixes v3 1/2] riscv: Fix enabling cbo.zero when running
 in M-mode

Hi Samuel,

On 14/02/2024 10:28, Andrew Jones wrote:
> On Wed, Feb 14, 2024 at 01:01:56AM -0800, Samuel Holland wrote:
>> When the kernel is running in M-mode, the CBZE bit must be set in the
>> menvcfg CSR, not in senvcfg.
>>
>> Cc: <stable@...r.kernel.org>
>> Fixes: 43c16d51a19b ("RISC-V: Enable cbo.zero in usermode")
>> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
>> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
>> ---
>>
>> (no changes since v1)
>>
>>   arch/riscv/include/asm/csr.h   | 2 ++
>>   arch/riscv/kernel/cpufeature.c | 2 +-
>>   2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
>> index 510014051f5d..2468c55933cd 100644
>> --- a/arch/riscv/include/asm/csr.h
>> +++ b/arch/riscv/include/asm/csr.h
>> @@ -424,6 +424,7 @@
>>   # define CSR_STATUS	CSR_MSTATUS
>>   # define CSR_IE		CSR_MIE
>>   # define CSR_TVEC	CSR_MTVEC
>> +# define CSR_ENVCFG	CSR_MENVCFG
>>   # define CSR_SCRATCH	CSR_MSCRATCH
>>   # define CSR_EPC	CSR_MEPC
>>   # define CSR_CAUSE	CSR_MCAUSE
>> @@ -448,6 +449,7 @@
>>   # define CSR_STATUS	CSR_SSTATUS
>>   # define CSR_IE		CSR_SIE
>>   # define CSR_TVEC	CSR_STVEC
>> +# define CSR_ENVCFG	CSR_SENVCFG
>>   # define CSR_SCRATCH	CSR_SSCRATCH
>>   # define CSR_EPC	CSR_SEPC
>>   # define CSR_CAUSE	CSR_SCAUSE
>> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> index 89920f84d0a3..c5b13f7dd482 100644
>> --- a/arch/riscv/kernel/cpufeature.c
>> +++ b/arch/riscv/kernel/cpufeature.c
>> @@ -950,7 +950,7 @@ arch_initcall(check_unaligned_access_all_cpus);
>>   void riscv_user_isa_enable(void)
>>   {
>>   	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
>> -		csr_set(CSR_SENVCFG, ENVCFG_CBZE);
>> +		csr_set(CSR_ENVCFG, ENVCFG_CBZE);
>>   }
>>   
>>   #ifdef CONFIG_RISCV_ALTERNATIVE
>> -- 
>> 2.43.0
>>
> After our back and forth on how we determine the existence of the *envcfg
> CSRs, I wonder if we shouldn't put a comment above this
> riscv_user_isa_enable() function capturing the [current] decision.
>
> Something like
>
>   /*
>    * While the [ms]envcfg CSRs weren't defined until priv spec 1.12,
>    * they're assumed to be present when an extension is present which
>    * specifies [ms]envcfg bit(s). Hence, we don't do any additional
>    * priv spec version checks or CSR probes here.
>    */

I was about to read the whole discussion in v2 to understand the 
v3...thank you Drew :) I think it really makes sense to add this 
comment, do you intend to do so Samuel?

Thanks,

Alex

>
> Thanks,
> drew
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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