selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/Documentation/trace/events-msr.rst b/Documentation/trace/events-msr.rst
new file mode 100644
index 000000000..35d06dc66
--- /dev/null
+++ b/Documentation/trace/events-msr.rst
@@ -0,0 +1,40 @@
+================
+MSR Trace Events
+================
+
+The x86 kernel supports tracing most MSR (Model Specific Register) accesses.
+To see the definition of the MSRs on Intel systems please see the SDM
+at https://www.intel.com/sdm (Volume 3)
+
+Available trace points:
+
+/sys/kernel/tracing/events/msr/
+
+Trace MSR reads:
+
+read_msr
+
+  - msr: MSR number
+  - val: Value written
+  - failed: 1 if the access failed, otherwise 0
+
+
+Trace MSR writes:
+
+write_msr
+
+  - msr: MSR number
+  - val: Value written
+  - failed: 1 if the access failed, otherwise 0
+
+
+Trace RDPMC in kernel:
+
+rdpmc
+
+The trace data can be post processed with the postprocess/decode_msr.py script::
+
+  cat /sys/kernel/tracing/trace | decode_msr.py /usr/src/linux/include/asm/msr-index.h
+
+to add symbolic MSR names.
+