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

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Message-ID: <864iwnedjk.wl-maz@kernel.org>
Date: Tue, 10 Jun 2025 18:01:35 +0100
From: Marc Zyngier <maz@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
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 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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.