Re: [PATCH V3 2/2] KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 10/06/25 10:31 PM, Marc Zyngier wrote:
> On Tue, 10 Jun 2025 06:31:28 +0100,
> Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>
>> Change MDSCR_EL1 register holding local variables as uint64_t that reflects
>> its true register width as well.
>>
>> Cc: Marc Zyngier <maz@kernel.org>
>> Cc: Oliver Upton <oliver.upton@linux.dev>
>> Cc: Joey Gouly <joey.gouly@arm.com>
>> Cc: kvm@vger.kernel.org
>> Cc: kvmarm@lists.linux.dev
>> Cc: linux-kernel@vger.kernel.org
>> Cc: linux-kselftest@vger.kernel.org
>> Cc: linux-arm-kernel@lists.infradead.org
>> Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>>  tools/testing/selftests/kvm/arm64/debug-exceptions.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/kvm/arm64/debug-exceptions.c b/tools/testing/selftests/kvm/arm64/debug-exceptions.c
>> index c7fb55c9135b..e34963956fbc 100644
>> --- a/tools/testing/selftests/kvm/arm64/debug-exceptions.c
>> +++ b/tools/testing/selftests/kvm/arm64/debug-exceptions.c
>> @@ -140,7 +140,7 @@ static void enable_os_lock(void)
>>  
>>  static void enable_monitor_debug_exceptions(void)
>>  {
>> -	uint32_t mdscr;
>> +	uint64_t mdscr;
>>  
>>  	asm volatile("msr daifclr, #8");
>>  
>> @@ -223,7 +223,7 @@ void install_hw_bp_ctx(uint8_t addr_bp, uint8_t ctx_bp, uint64_t addr,
>>  
>>  static void install_ss(void)
>>  {
>> -	uint32_t mdscr;
>> +	uint64_t mdscr;
>>  
>>  	asm volatile("msr daifclr, #8");
>>  
> 
> Why change this in the place that matters *the least*?
> 
> arch/arm64/kernel/debug-monitors.c is full of 32bit manipulation of
> this register, and that's only one example of it. So if you are going
> to change this, please do it fully, not as a random change in a random
> file.

The first patch in this series changes mdscr system register to 64 bit
in the mentioned file (i.e arch/arm64/kernel/debug-monitors.c). 

> 
> Thanks,
> 
> 	M.
>