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, 36 insertions, 0 deletions

diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
new file mode 100644
index 000000000..650e804d0
--- /dev/null
+++ b/tools/perf/util/smt.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <string.h>
+#include "api/fs/fs.h"
+#include "cputopo.h"
+#include "smt.h"
+
+bool smt_on(void)
+{
+	static bool cached;
+	static bool cached_result;
+	int fs_value;
+
+	if (cached)
+		return cached_result;
+
+	if (sysfs__read_int("devices/system/cpu/smt/active", &fs_value) >= 0)
+		cached_result = (fs_value == 1);
+	else
+		cached_result = cpu_topology__smt_on(online_topology());
+
+	cached = true;
+	return cached_result;
+}
+
+bool core_wide(bool system_wide, const char *user_requested_cpu_list)
+{
+	/* If not everything running on a core is being recorded then we can't use core_wide. */
+	if (!system_wide)
+		return false;
+
+	/* Cheap case that SMT is disabled and therefore we're inherently core_wide. */
+	if (!smt_on())
+		return true;
+
+	return cpu_topology__core_wide(online_topology(), user_requested_cpu_list);
+}