[PATCH V5 0/2] arm64/debug: Drop redundant DBG_MDSCR_* macros

[PATCH V5 0/2] arm64/debug: Drop redundant DBG_MDSCR_* macros

[Anshuman Khandual]

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.

This series applies on v6.16-rc1

Changes in V5:

- Replaced open encoding with MDSCR_EL1_TDCC in __cpu_setup()

Changes in V4:

https://lore.kernel.org/all/20250612033547.480952-1-anshuman.khandual@arm.com/

- Updated the commit message in [PATCH 1/2] explainig rationale for changing
  mdscr variable as u64 per Mark

Changes in V3:

https://lore.kernel.org/all/20250610053128.4118784-1-anshuman.khandual@arm.com/

- Split out the self test changes into a separate patch per Mark
- Added RB tag from Ada

Changes in V2:

https://lore.kernel.org/all/20250508044752.234543-1-anshuman.khandual@arm.com/

- Changed reg, val width to u64 in cortex_a76_erratum_1463225_svc_handler() per Ada
- Changed mdscr register width to uint64_t in enable_monitor_debug_exceptions() and
  install_ss() per Ada
    
Changes in V1:

https://lore.kernel.org/all/20250417105253.3188976-1-anshuman.khandual@arm.com/

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: kvmarm@lists.linux.dev
Cc: kvm@vger.kernel.org

Anshuman Khandual (2):
  arm64/debug: Drop redundant DBG_MDSCR_* macros
  KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t

 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 ++--
 arch/arm64/mm/proc.S                          |  2 +-
 .../selftests/kvm/arm64/debug-exceptions.c    |  4 ++--
 6 files changed, 18 insertions(+), 24 deletions(-)

-- 
2.25.1

[PATCH V5 1/2] arm64/debug: Drop redundant DBG_MDSCR_* macros

[Anshuman Khandual]

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;
      |             ^
--------------------------------------------------------------------------

While here, replace an open encoding with MDSCR_EL1_TDCC in __cpu_setup().

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 ++--
 arch/arm64/mm/proc.S                    |  2 +-
 5 files changed, 16 insertions(+), 22 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();
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 80d470aa469d..eabf97c71dbf 100644
--- 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
-- 
2.25.1

[PATCH V5 2/2] KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t

[Anshuman Khandual]

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");
 
-- 
2.25.1

Re: [PATCH V5 0/2] arm64/debug: Drop redundant DBG_MDSCR_* macros

[Catalin Marinas]

On Fri, 13 Jun 2025 08:06:44 +0530, 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.
> 
> This series applies on v6.16-rc1
> 
> [...]

Applied to arm64 (for-next/mdscr-cleanup), thanks!

[1/2] arm64/debug: Drop redundant DBG_MDSCR_* macros
      https://git.kernel.org/arm64/c/d3a80c5109a3
[2/2] KVM: selftests: Change MDSCR_EL1 register holding variables as uint64_t
      https://git.kernel.org/arm64/c/30ff3c981e48

-- 
Catalin