Re: [PATCH V4 1/2] arm64/debug: Drop redundant DBG_MDSCR_* macros

Anshuman Khandual
2025-06-12T10:24:11Z

On 12/06/25 1:47 PM, Marc Zyngier wrote:
> On Thu, 12 Jun 2025 04:35:46 +0100,
> Anshuman Khandual <anshuman.khandual@arm.com> wrote:
>>
>> MDSCR_EL1 has already been defined in tools sysreg format and hence can be
>> used in all debug monitor related call paths. But using generated sysreg
>> definitions causes build warnings because there is a mismatch between mdscr
>> variable (u32) and GENMASK() based masks (long unsigned int). Convert all
>> variables handling MDSCR_EL1 register as u64 which also reflects its true
>> width as well.
>>
>> --------------------------------------------------------------------------
>> arch/arm64/kernel/debug-monitors.c: In function ‘disable_debug_monitors’:
>> arch/arm64/kernel/debug-monitors.c:108:13: warning: conversion from ‘long
>> unsigned int’ to ‘u32’ {aka ‘unsigned int’} changes value from
>> ‘18446744073709518847’ to ‘4294934527’ [-Woverflow]
>> 108 | disable = ~MDSCR_EL1_MDE;
>> | ^
>> --------------------------------------------------------------------------
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>> arch/arm64/include/asm/assembler.h | 4 ++--
>> arch/arm64/include/asm/debug-monitors.h | 6 ------
>> arch/arm64/kernel/debug-monitors.c | 22 +++++++++++-----------
>> arch/arm64/kernel/entry-common.c | 4 ++--
>> 4 files changed, 15 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
>> index ad63457a05c5..f229d96616e5 100644
>> --- a/arch/arm64/include/asm/assembler.h
>> +++ b/arch/arm64/include/asm/assembler.h
>> @@ -53,7 +53,7 @@
>> .macro disable_step_tsk, flgs, tmp
>> tbz \flgs, #TIF_SINGLESTEP, 9990f
>> mrs \tmp, mdscr_el1
>> - bic \tmp, \tmp, #DBG_MDSCR_SS
>> + bic \tmp, \tmp, #MDSCR_EL1_SS
>> msr mdscr_el1, \tmp
>> isb // Take effect before a subsequent clear of DAIF.D
>> 9990:
>> @@ -63,7 +63,7 @@
>> .macro enable_step_tsk, flgs, tmp
>> tbz \flgs, #TIF_SINGLESTEP, 9990f
>> mrs \tmp, mdscr_el1
>> - orr \tmp, \tmp, #DBG_MDSCR_SS
>> + orr \tmp, \tmp, #MDSCR_EL1_SS
>> msr mdscr_el1, \tmp
>> 9990:
>> .endm
>> diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
>> index 8f6ba31b8658..1f37dd01482b 100644
>> --- a/arch/arm64/include/asm/debug-monitors.h
>> +++ b/arch/arm64/include/asm/debug-monitors.h
>> @@ -13,14 +13,8 @@
>> #include <asm/ptrace.h>
>>
>> /* Low-level stepping controls. */
>> -#define DBG_MDSCR_SS (1 << 0)
>> #define DBG_SPSR_SS (1 << 21)
>>
>> -/* MDSCR_EL1 enabling bits */
>> -#define DBG_MDSCR_KDE (1 << 13)
>> -#define DBG_MDSCR_MDE (1 << 15)
>> -#define DBG_MDSCR_MASK ~(DBG_MDSCR_KDE | DBG_MDSCR_MDE)
>> -
>> #define DBG_ESR_EVT(x) (((x) >> 27) & 0x7)
>>
>> /* AArch64 */
>> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
>> index 58f047de3e1c..08f1d02507cd 100644
>> --- a/arch/arm64/kernel/debug-monitors.c
>> +++ b/arch/arm64/kernel/debug-monitors.c
>> @@ -34,7 +34,7 @@ u8 debug_monitors_arch(void)
>> /*
>> * MDSCR access routines.
>> */
>> -static void mdscr_write(u32 mdscr)
>> +static void mdscr_write(u64 mdscr)
>> {
>> unsigned long flags;
>> flags = local_daif_save();
>> @@ -43,7 +43,7 @@ static void mdscr_write(u32 mdscr)
>> }
>> NOKPROBE_SYMBOL(mdscr_write);
>>
>> -static u32 mdscr_read(void)
>> +static u64 mdscr_read(void)
>> {
>> return read_sysreg(mdscr_el1);
>> }
>> @@ -79,16 +79,16 @@ static DEFINE_PER_CPU(int, kde_ref_count);
>>
>> void enable_debug_monitors(enum dbg_active_el el)
>> {
>> - u32 mdscr, enable = 0;
>> + u64 mdscr, enable = 0;
>>
>> WARN_ON(preemptible());
>>
>> if (this_cpu_inc_return(mde_ref_count) == 1)
>> - enable = DBG_MDSCR_MDE;
>> + enable = MDSCR_EL1_MDE;
>>
>> if (el == DBG_ACTIVE_EL1 &&
>> this_cpu_inc_return(kde_ref_count) == 1)
>> - enable |= DBG_MDSCR_KDE;
>> + enable |= MDSCR_EL1_KDE;
>>
>> if (enable && debug_enabled) {
>> mdscr = mdscr_read();
>> @@ -100,16 +100,16 @@ NOKPROBE_SYMBOL(enable_debug_monitors);
>>
>> void disable_debug_monitors(enum dbg_active_el el)
>> {
>> - u32 mdscr, disable = 0;
>> + u64 mdscr, disable = 0;
>>
>> WARN_ON(preemptible());
>>
>> if (this_cpu_dec_return(mde_ref_count) == 0)
>> - disable = ~DBG_MDSCR_MDE;
>> + disable = ~MDSCR_EL1_MDE;
>>
>> if (el == DBG_ACTIVE_EL1 &&
>> this_cpu_dec_return(kde_ref_count) == 0)
>> - disable &= ~DBG_MDSCR_KDE;
>> + disable &= ~MDSCR_EL1_KDE;
>>
>> if (disable) {
>> mdscr = mdscr_read();
>> @@ -415,7 +415,7 @@ void kernel_enable_single_step(struct pt_regs *regs)
>> {
>> WARN_ON(!irqs_disabled());
>> set_regs_spsr_ss(regs);
>> - mdscr_write(mdscr_read() | DBG_MDSCR_SS);
>> + mdscr_write(mdscr_read() | MDSCR_EL1_SS);
>> enable_debug_monitors(DBG_ACTIVE_EL1);
>> }
>> NOKPROBE_SYMBOL(kernel_enable_single_step);
>> @@ -423,7 +423,7 @@ NOKPROBE_SYMBOL(kernel_enable_single_step);
>> void kernel_disable_single_step(void)
>> {
>> WARN_ON(!irqs_disabled());
>> - mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
>> + mdscr_write(mdscr_read() & ~MDSCR_EL1_SS);
>> disable_debug_monitors(DBG_ACTIVE_EL1);
>> }
>> NOKPROBE_SYMBOL(kernel_disable_single_step);
>> @@ -431,7 +431,7 @@ NOKPROBE_SYMBOL(kernel_disable_single_step);
>> int kernel_active_single_step(void)
>> {
>> WARN_ON(!irqs_disabled());
>> - return mdscr_read() & DBG_MDSCR_SS;
>> + return mdscr_read() & MDSCR_EL1_SS;
>> }
>> NOKPROBE_SYMBOL(kernel_active_single_step);
>>
>> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
>> index 7c1970b341b8..171f93f2494b 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;
>> @@ -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();
>
> Whilst you're at it, please also change the open-coded constant in
> __cpu_setup to MDSCR_EL1_TDCC.

I believe you are suggesting about the following change, will fold
in the patch. But I guess 'mov' would still be preferred compared
to 'mov_q' as MDSCR_EL1_TDCC is a 32 bit constant (atleast the non
zero portion) ?

--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -454,7 +454,7 @@ SYM_FUNC_START(__cpu_setup)
dsb nsh

msr cpacr_el1, xzr // Reset cpacr_el1
- mov x1, #1 << 12 // Reset mdscr_el1 and disable
+ mov x1, MDSCR_EL1_TDCC // Reset mdscr_el1 and disable
msr mdscr_el1, x1 // access to the DCC from EL0
reset_pmuserenr_el0 x1 // Disable PMU access from EL0
reset_amuserenr_el0 x1 // Disable AMU access from EL0