bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/xen.rst b/Documentation/admin-guide/sysctl/xen.rst
new file mode 100644
index 000000000..6c5edc3e5
--- /dev/null
+++ b/Documentation/admin-guide/sysctl/xen.rst
@@ -0,0 +1,31 @@
+===============
+/proc/sys/xen/
+===============
+
+Copyright (c) 2026, Shubham Chakraborty <chakrabortyshubham66@gmail.com>
+
+For general info and legal blurb, please look in
+Documentation/admin-guide/sysctl/index.rst.
+
+------------------------------------------------------------------------------
+
+These files show up in ``/proc/sys/xen/``, depending on the
+kernel configuration:
+
+.. contents:: :local:
+
+balloon/hotplug_unpopulated
+===========================
+
+This flag controls whether unpopulated memory ranges are automatically
+hotplugged as system RAM.
+
+- ``0``: Unpopulated ranges are not hotplugged (default).
+- ``1``: Unpopulated ranges are automatically hotplugged.
+
+When enabled, the Xen balloon driver will add memory regions that are
+marked as unpopulated in the Xen memory map to the system as usable RAM.
+This allows for dynamic memory expansion in Xen guest domains.
+
+This option is only available when the kernel is built with
+``CONFIG_XEN_BALLOON_MEMORY_HOTPLUG`` enabled.