executor: prevent "NMI handler took too long" messages

nmi_check_duration() prints "INFO: NMI handler took too long" on slow debug kernels.
It happens a lot in qemu, and the messages are frequently corrupted
(intermixed with other kernel output as they are printed from NMI)
and are not matched against the suppression in pkg/report.
This write prevents these messages from being printed.

2 files changed, 16 insertions, 0 deletions

diff --git a/executor/executor.cc b/executor/executor.cc
index 2635d5a7c..768081ad6 100644
--- a/executor/executor.cc
+++ b/executor/executor.cc
@@ -1404,6 +1404,10 @@ void setup_features(char** enable, int n)
 {
 	// This does any one-time setup for the requested features on the machine.
 	// Note: this can be called multiple times and must be idempotent.
+#if SYZ_HAVE_FEATURES
+	// Note: this is not executed in C reproducers.
+	setup_machine();
+#endif
 	for (int i = 0; i < n; i++) {
 		bool found = false;
 #if SYZ_HAVE_FEATURES
diff --git a/executor/executor_linux.h b/executor/executor_linux.h
index 63c900c5a..d4220c23f 100644
--- a/executor/executor_linux.h
+++ b/executor/executor_linux.h
@@ -225,3 +225,15 @@ static feature_t features[] = {
     {"binfmt_misc", setup_binfmt_misc},
     {"kcsan", setup_kcsan},
 };
+
+static void setup_machine()
+{
+	// nmi_check_duration() prints "INFO: NMI handler took too long" on slow debug kernels.
+	// It happens a lot in qemu, and the messages are frequently corrupted
+	// (intermixed with other kernel output as they are printed from NMI)
+	// and are not matched against the suppression in pkg/report.
+	// This write prevents these messages from being printed.
+	// Note: this is not executed in C reproducers.
+	if (!write_file("/sys/kernel/debug/x86/nmi_longest_ns", "10000000000"))
+		printf("write to /sys/kernel/debug/x86/nmi_longest_ns failed: %s\n", strerror(errno));
+}