arm64/boot: Disable trapping of PMZR_EL0 writes to EL2grafted

__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 <fuad.tabba@linux.dev>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 73 insertions, 0 deletions

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 <process_howto>`; also read
+:ref:`process/submitting-patches.rst <submittingpatches>`. 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.