linux-kernel - Re: [PATCH V3 2/2] KVM: selftests: Change MDSCR_EL1 register holding variables as uint64

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Message-ID: <9b378582-44eb-4fbb-a03a-40eb317daebd@arm.com>
Date: Wed, 11 Jun 2025 09:15:10 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Ada Couprie Diaz <ada.coupriediaz@....com>, linux-kernel@...r.kernel.org,
 Oliver Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>,
 kvm@...r.kernel.org, kvmarm@...ts.linux.dev, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH V3 2/2] KVM: selftests: Change MDSCR_EL1 register holding
 variables as uint64_t



On 10/06/25 10:31 PM, Marc Zyngier wrote:
> On Tue, 10 Jun 2025 06:31:28 +0100,
> Anshuman Khandual <anshuman.khandual@....com> wrote:
>>
>> Change MDSCR_EL1 register holding local variables as uint64_t that reflects
>> its true register width as well.
>>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Cc: Oliver Upton <oliver.upton@...ux.dev>
>> Cc: Joey Gouly <joey.gouly@....com>
>> Cc: kvm@...r.kernel.org
>> Cc: kvmarm@...ts.linux.dev
>> Cc: linux-kernel@...r.kernel.org
>> Cc: linux-kselftest@...r.kernel.org
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@....com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....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.
>