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/8.Conclusion.rst | 73 ++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 Documentation/process/8.Conclusion.rst (limited to 'Documentation/process/8.Conclusion.rst') diff --git a/Documentation/process/8.Conclusion.rst b/Documentation/process/8.Conclusion.rst new file mode 100644 index 000000000..8c847dffe --- /dev/null +++ b/Documentation/process/8.Conclusion.rst @@ -0,0 +1,73 @@ +.. _development_conclusion: + +For more information +==================== + +There are numerous sources of information on Linux kernel development and +related topics. First among those will always be the Documentation +directory found in the kernel source distribution. Start with the +top-level :ref:`process/howto.rst `; also read +:ref:`process/submitting-patches.rst `. Many internal +kernel APIs are documented using the kerneldoc mechanism; "make htmldocs" +or "make pdfdocs" can be used to generate those documents in HTML or PDF +format (though the version of TeX shipped by some distributions runs into +internal limits and fails to process the documents properly). + +Various web sites discuss kernel development at all levels of detail. Your +author would like to humbly suggest https://lwn.net/ as a source; +information on many specific kernel topics can be found via the LWN kernel +index at: + + https://lwn.net/Kernel/Index/ + +Beyond that, a valuable resource for kernel developers is: + + https://kernelnewbies.org/ + +And, of course, one should not forget https://kernel.org/, the definitive +location for kernel release information. + +There are a number of books on kernel development: + + Linux Device Drivers, 3rd Edition (Jonathan Corbet, Alessandro + Rubini, and Greg Kroah-Hartman). Online at + https://lwn.net/Kernel/LDD3/. + + Linux Kernel Development (Robert Love). + + Understanding the Linux Kernel (Daniel Bovet and Marco Cesati). + +All of these books suffer from a common fault, though: they tend to be +somewhat obsolete by the time they hit the shelves, and they have been on +the shelves for a while now. Still, there is quite a bit of good +information to be found there. + +Documentation for git can be found at: + + https://www.kernel.org/pub/software/scm/git/docs/ + + https://www.kernel.org/pub/software/scm/git/docs/user-manual.html + + +Conclusion +========== + +Congratulations to anybody who has made it through this long-winded +document. Hopefully it has provided a helpful understanding of how the +Linux kernel is developed and how you can participate in that process. + +In the end, it's the participation that matters. Any open source software +project is no more than the sum of what its contributors put into it. The +Linux kernel has progressed as quickly and as well as it has because it has +been helped by an impressively large group of developers, all of whom are +working to make it better. The kernel is a premier example of what can be +done when thousands of people work together toward a common goal. + +The kernel can always benefit from a larger developer base, though. There +is always more work to do. But, just as importantly, most other +participants in the Linux ecosystem can benefit through contributing to the +kernel. Getting code into the mainline is the key to higher code quality, +lower maintenance and distribution costs, a higher level of influence over +the direction of kernel development, and more. It is a situation where +everybody involved wins. Fire up your editor and come join us; you will be +more than welcome. -- cgit v1.3.1