Subject: [PATCH v4 0/6] arm64: Add support for FEAT_Debugv8p9

From: "Rob Herring (Arm)" <[email-masked]>
Date: Tue, 07 Apr 2026 09:29:42 -0500

This series enables FEAT_Debugv8p9 which extends the breakpoint and 
watchpoint support from 16 up to 64. I've picked up this series from 
Anshuman.

Changes in V4:

- Limit enabling of FEAT_Debugv8p9 to only when more than 16 breakpoints 
  or watchpoints are present.
- Add lockdep_assert_irqs_disabled() to document the constraints. Drop 
  unnecessary IRQ disabling.
- Add more kprobe blacklist annotations and disallow breakpoints in the 
  nokprobe code.
- Drop previously applied sysreg patches.

Prior versions from Anshuman:

Changes in V3:

https://lore.kernel.org/all/[email-masked]/

- Marked ID_AA64DFR1_EL1.ABLE as FTR_NONSTRICT in ftr_id_aa64dfr1[]
- Dropped MDCR_EL3.TDA boot requirement from documentation (separate series)
- Dropped MDCR_EL2_EBWE definition as MDCR_EL2 is now defined in tools sysreg
- Used SYS_FIELD_PREP() in read_wb_reg() and write_wb_reg()
- Added MAX_PER_BANK based BUILD_BUG_ON() tests in arch_hw_breakpoint_init()
- Dropped local variables i.e mdsel_bank and index
- Derived bank and index from MAX_PER_BANK as required

Changes in V2:

https://lore.kernel.org/all/[email-masked]/

Following changes have been made per review comments from Mark Rutland

- Orr MDCR_EL2_EBWE directly without an intermittent register
- Alphabetically order header files in debug-monitors.c
- Dropped embwe_ref_count mechanism
- Dropped preempt_enable() from AARCH64_DBG_READ
- Dropped preempt_disable() from AARCH64_DBG_WRITE
- Dropped set_bank_index()
- Renamed read/write_wb_reg() as __read/__write_wb_reg()
- Modified read/write_wb_reg() to have MDSELR_E1 based banked read/write
- Added required sysreg tools patches from KVM FEAT_FGT2 series for build

Changes in V1:

https://lore.kernel.org/all/[email-masked]/

- Changed FTR_STRICT to FTR_NONSTRICT for the following ID_AA64DFR1_EL1
  register fields - ABL_CMPs, DPFZS, PMICNTR, CTX_CMPs, WRPs and BRPs

Changes in RFC V2:

https://lore.kernel.org/linux-arm-kernel/[email-masked]/

- This series has been split from RFC V1 dealing only with arm64 breakpoints
- Restored back DBG_MDSCR_MASK definition (unrelated change)
- Added preempt_disable()/enable() blocks between selecting banks and registers

Changes in RFC:

https://lore.kernel.org/all/[email-masked]/

Signed-off-by: Rob Herring (Arm) <[email-masked]>
---
Anshuman Khandual (3):
      arm64/cpufeature: Add field details for ID_AA64DFR1_EL1 register
      arm64/boot: Enable EL2 requirements for FEAT_Debugv8p9
      arm64: hw_breakpoint: Enable FEAT_Debugv8p9

Rob Herring (Arm) (3):
      arm64: hw_breakpoint: Disallow breakpoints in no kprobe code
      arm64: hw_breakpoint: Add additional kprobe excluded functions
      arm64: hw_breakpoint: Add lockdep_assert_irqs_disabled() on install/uninstall

 Documentation/arch/arm64/booting.rst   | 13 +++++++
 arch/arm64/include/asm/el2_setup.h     | 14 +++++++
 arch/arm64/include/asm/hw_breakpoint.h | 47 ++++++++++++++++++-----
 arch/arm64/kernel/cpufeature.c         | 21 ++++++++---
 arch/arm64/kernel/debug-monitors.c     | 16 +++++---
 arch/arm64/kernel/hw_breakpoint.c      | 68 +++++++++++++++++++++++++++++-----
 6 files changed, 150 insertions(+), 29 deletions(-)
---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260406-arm-debug-8-9-41f6f0e739b5

Best regards,
--  
Rob Herring (Arm) <[email-masked]>