From 2bc6b218717b9d08f466f88209251d54bc09b207 Mon Sep 17 00:00:00 2001 From: Fuad Tabba Date: Tue, 22 Sep 2026 19:14:30 +0100 Subject: arm64/boot: Disable trapping of PMZR_EL0 writes to EL2 __init_el2_fgt2() writes one mask to both HDFGRTR2_EL2 and HDFGWTR2_EL2. PMZR_EL0 is write-only, so its trap bit, nPMZR_EL0, exists only in HDFGWTR2_EL2 and is therefore never set: a PMZR_EL0 write from the host traps to EL2, where the nVHE hypervisor has no handler and BUG()s. The kernel never writes PMZR_EL0, but kernel.perf_user_access=1 has the PMU driver set PMUSERENR_EL0.UEN for a task with a user-read event, so a write from EL0 reaches the trap and takes the host down without a panic message. Accumulate the HDFGWTR2_EL2 bits separately, as __init_el2_fgt() already does for HDFGWTR_EL2, and set nPMZR_EL0 with the other FEAT_PMUv3p9 bits. Fixes: 858c7bfcb35e1 ("arm64/boot: Enable EL2 requirements for FEAT_PMUv3p9") Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Reviewed-by: Anshuman Khandual Reviewed-by: Oliver Upton Signed-off-by: Will Deacon --- Documentation/process/debugging/index.rst | 71 +++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) create mode 100644 Documentation/process/debugging/index.rst (limited to 'Documentation/process/debugging/index.rst') diff --git a/Documentation/process/debugging/index.rst b/Documentation/process/debugging/index.rst new file mode 100644 index 000000000..357243e18 --- /dev/null +++ b/Documentation/process/debugging/index.rst @@ -0,0 +1,71 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================ +Debugging advice for Linux Kernel developers +============================================ + +general guides +-------------- + +.. toctree:: + :maxdepth: 1 + + driver_development_debugging_guide + gdb-kernel-debugging + kgdb + userspace_debugging_guide + +subsystem specific guides +------------------------- + +.. toctree:: + :maxdepth: 1 + + media_specific_debugging_guide + +General debugging advice +======================== + +Depending on the issue, a different set of tools is available to track down the +problem or even to realize whether there is one in the first place. + +As a first step you have to figure out what kind of issue you want to debug. +Depending on the answer, your methodology and choice of tools may vary. + +Do I need to debug with limited access? +--------------------------------------- + +Do you have limited access to the machine or are you unable to stop the running +execution? + +In this case your debugging capability depends on built-in debugging support of +provided distribution kernel. +The :doc:`/process/debugging/userspace_debugging_guide` provides a brief +overview over a range of possible debugging tools in that situation. You can +check the capability of your kernel, in most cases, by looking into config file +within the /boot directory. + +Do I have root access to the system? +------------------------------------ + +Are you easily able to replace the module in question or to install a new +kernel? + +In that case your range of available tools is a lot bigger, you can find the +tools in the :doc:`/process/debugging/driver_development_debugging_guide`. + +Is timing a factor? +------------------- + +It is important to understand if the problem you want to debug manifests itself +consistently (i.e. given a set of inputs you always get the same, incorrect +output), or inconsistently. If it manifests itself inconsistently, some timing +factor might be at play. If inserting delays into the code does change the +behavior, then quite likely timing is a factor. + +When timing does alter the outcome of the code execution using a simple +printk() for debugging purposes may not work, a similar alternative is to use +trace_printk() , which logs the debug messages to the trace file instead of the +kernel log. + +**Copyright** ©2024 : Collabora -- cgit v1.3.1