linux-kernel - Re: [PATCH] arm64/debug: Drop redundant DBG_MDSCR

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Message-ID: <566f9bba-6cc9-490c-aacc-9edd0ae441a0@arm.com>
Date: Tue, 6 May 2025 14:15:10 +0100
From: Ada Couprie Diaz <ada.coupriediaz@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
 linux-arm-kernel@...ts.infradead.org
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Ada Couprie Diaz <ada.coupriediaz@....com>
Subject: Re: [PATCH] arm64/debug: Drop redundant DBG_MDSCR_* macros

+ linux-arm-kernel@...ts.infradead.org

I forgot to fix the typo for the linux-arm-kernel mailing list while 
replying-all to the original patch, adding it back.

Apologies.

On 06/05/2025 14:10, Ada Couprie Diaz wrote:
> Hi Anshuman,
>
> On 17/04/2025 11:52, Anshuman Khandual wrote:
>> MDSCR_EL1 has already been defined in tools sysreg format and hence 
>> can be
>> used in all debug monitor related call paths. Subsequently all 
>> DBG_MDSCR_*
>> macros become redundant and hence can be dropped off completely. 
>> While here
>> convert all variables handling MDSCR_EL1 register as u64 which 
>> reflects its
>> true width as well.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>
> I think the changes make sense, even more so given that `kvm/debug.c` 
> already uses the sysreg format definition for MDSCR_EL1.
>
> It looks good to me, but I think there is a missing conversion to 64 
> bits below.
> Would it make sense to convert the two instances of MDSCR_EL1 used in 
> `tools/testing/selftests/kvm/arm64/debug-exceptions.c`, in 
> `enable_monitor_debug_exceptions()` and `install_ss()` , to 64 bits as 
> well ? (They don't rely on `DBG_MDSCR_*`, the test defines its own 
> macros)
>
>> diff --git a/arch/arm64/kernel/entry-common.c 
>> b/arch/arm64/kernel/entry-common.c
>> index b260ddc4d3e9..6dbfc1008007 100644
>> --- a/arch/arm64/kernel/entry-common.c
>> +++ b/arch/arm64/kernel/entry-common.c
>> @@ -354,7 +354,7 @@ static void 
>> cortex_a76_erratum_1463225_svc_handler(void)
>>         __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1);
>>       reg = read_sysreg(mdscr_el1);
>> -    val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE;
>> +    val = reg | MDSCR_EL1_SS | MDSCR_EL1_KDE;
>>       write_sysreg(val, mdscr_el1);
>>       asm volatile("msr daifclr, #8");
>>       isb();
>
> Given the change of width to 64 bits elsewhere, shouldn't we change 
> val and reg to u64 here as well ?
>
> diff --git a/arch/arm64/kernel/entry-common.c 
> b/arch/arm64/kernel/entry-common.c
> index 73cf6a5f41d8..d61a5ddf53d6 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -344,7 +344,7 @@ static DEFINE_PER_CPU(int, 
> __in_cortex_a76_erratum_1463225_wa);
>
>  static void cortex_a76_erratum_1463225_svc_handler(void)
>  {
> -    u32 reg, val;
> +    u64 reg, val;
>
>      if (!unlikely(test_thread_flag(TIF_SINGLESTEP)))
>          return;
>
> Thanks,
> Ada
>