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, 35 insertions, 0 deletions

diff --git a/Documentation/virt/paravirt_ops.rst b/Documentation/virt/paravirt_ops.rst
new file mode 100644
index 000000000..62d867e0d
--- /dev/null
+++ b/Documentation/virt/paravirt_ops.rst
@@ -0,0 +1,35 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+Paravirt_ops
+============
+
+Linux provides support for different hypervisor virtualization technologies.
+Historically, different binary kernels would be required in order to support
+different hypervisors; this restriction was removed with pv_ops.
+Linux pv_ops is a virtualization API which enables support for different
+hypervisors. It allows each hypervisor to override critical operations and
+allows a single kernel binary to run on all supported execution environments
+including native machine -- without any hypervisors.
+
+pv_ops provides a set of function pointers which represent operations
+corresponding to low-level critical instructions and high-level
+functionalities in various areas. pv_ops allows for optimizations at run
+time by enabling binary patching of the low-level critical operations
+at boot time.
+
+pv_ops operations are classified into three categories:
+
+- simple indirect call
+   These operations correspond to high-level functionality where it is
+   known that the overhead of indirect call isn't very important.
+
+- indirect call which allows optimization with binary patch
+   Usually these operations correspond to low-level critical instructions. They
+   are called frequently and are performance critical. The overhead is
+   very important.
+
+- a set of macros for hand written assembly code
+   Hand written assembly codes (.S files) also need paravirtualization
+   because they include sensitive instructions or some code paths in
+   them are very performance critical.