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/admin-guide/sysctl/debug.rst | 52 ++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 Documentation/admin-guide/sysctl/debug.rst (limited to 'Documentation/admin-guide/sysctl/debug.rst') diff --git a/Documentation/admin-guide/sysctl/debug.rst b/Documentation/admin-guide/sysctl/debug.rst new file mode 100644 index 000000000..506bd5e48 --- /dev/null +++ b/Documentation/admin-guide/sysctl/debug.rst @@ -0,0 +1,52 @@ +================ +/proc/sys/debug/ +================ + +These files show up in ``/proc/sys/debug/``, depending on the +kernel configuration: + +.. contents:: :local: + +exception-trace +=============== + +This flag controls whether the kernel prints information about unhandled +signals (like segmentation faults) to the kernel log (``dmesg``). + +- ``0``: Unhandled signals are not traced. +- ``1``: Information about unhandled signals is printed. + +The default value is ``1`` on most architectures (like x86, MIPS, RISC-V), +but it is ``0`` on **arm64**. + +The actual information printed and the context provided varies +significantly depending on the CPU architecture. For example: + +- On **x86**, it typically prints the instruction pointer (IP), error + code, and address that caused a page fault. +- On **PowerPC**, it may print the next instruction pointer (NIP), + link register (LR), and other relevant registers. + +When enabled, this feature is often rate-limited to prevent the kernel +log from being flooded during a crash loop. + +kprobes-optimization +==================== + +This flag enables or disables the optimization of Kprobes on certain +architectures (like x86). + +- ``0``: Kprobes optimization is turned off. +- ``1``: Kprobes optimization is turned on (default). + +For more details on Kprobes and its optimization, please refer to +Documentation/trace/kprobes.rst. + +Copyright (c) 2026, Shubham Chakraborty + +For general info and legal blurb, please look in +Documentation/admin-guide/sysctl/index.rst. + +.. See scripts/check-sysctl-docs to keep this up to date: +.. scripts/check-sysctl-docs -vtable="debug" \ +.. $(git grep -l register_sysctl_) -- cgit v1.3.1