From 119e9db233ad0f4cbd4cfb9f9385a7bca378b37d Mon Sep 17 00:00:00 2001
From: Zeng Chi <zengchi@kylinos.cn>
Date: Mon, 21 Sep 2026 18:24:42 +0800
Subject: KVM: Don't pre-reserve xarray entries when storing empty/NULL
 attributes

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/objtool/signal.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 tools/objtool/signal.c

(limited to 'tools/objtool/signal.c')

diff --git a/tools/objtool/signal.c b/tools/objtool/signal.c
new file mode 100644
index 000000000..af5c65c0f
--- /dev/null
+++ b/tools/objtool/signal.c
@@ -0,0 +1,135 @@
+/*
+ * signal.c: Register a sigaltstack for objtool, to be able to
+ *	     run a signal handler on a separate stack even if
+ *	     the main process stack has overflown. Print out
+ *	     stack overflow errors when this happens.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/resource.h>
+#include <string.h>
+
+#include <objtool/objtool.h>
+#include <objtool/warn.h>
+
+static unsigned long stack_limit;
+
+static bool is_stack_overflow(void *fault_addr)
+{
+	unsigned long fault = (unsigned long)fault_addr;
+
+	/* Check if fault is in the guard page just below the limit. */
+	return fault < stack_limit && fault >= stack_limit - 4096;
+}
+
+static void signal_handler(int sig_num, siginfo_t *info, void *context)
+{
+	struct sigaction sa_dfl = {0};
+	const char *sig_name;
+	char msg[256];
+	int msg_len;
+
+	switch (sig_num) {
+	case SIGSEGV:	sig_name = "SIGSEGV";		break;
+	case SIGBUS:	sig_name = "SIGBUS";		break;
+	case SIGILL:	sig_name = "SIGILL";		break;
+	case SIGABRT:	sig_name = "SIGABRT";		break;
+	default:	sig_name = "Unknown signal";	break;
+	}
+
+	if (is_stack_overflow(info->si_addr)) {
+		msg_len = snprintf(msg, sizeof(msg),
+				   "%s: error: %s: objtool stack overflow!\n",
+				   objname, sig_name);
+	} else {
+		msg_len = snprintf(msg, sizeof(msg),
+				   "%s: error: %s: objtool crash!\n",
+				   objname, sig_name);
+	}
+
+	msg_len = write(STDERR_FILENO, msg, msg_len);
+
+	/* Re-raise the signal to trigger the core dump */
+	sa_dfl.sa_handler = SIG_DFL;
+	sigaction(sig_num, &sa_dfl, NULL);
+	raise(sig_num);
+}
+
+static int read_stack_limit(void)
+{
+	unsigned long stack_start, stack_end;
+	struct rlimit rlim;
+	char line[256];
+	int ret = 0;
+	FILE *fp;
+
+	if (getrlimit(RLIMIT_STACK, &rlim)) {
+		ERROR_GLIBC("getrlimit");
+		return -1;
+	}
+
+	fp = fopen("/proc/self/maps", "r");
+	if (!fp) {
+		ERROR_GLIBC("fopen");
+		return -1;
+	}
+
+	while (fgets(line, sizeof(line), fp)) {
+		if (strstr(line, "[stack]")) {
+			if (sscanf(line, "%lx-%lx", &stack_start, &stack_end) != 2) {
+				ERROR_GLIBC("sscanf");
+				ret = -1;
+				goto done;
+			}
+			stack_limit = stack_end - rlim.rlim_cur;
+			goto done;
+		}
+	}
+
+	ret = -1;
+	ERROR("/proc/self/maps: can't find [stack]");
+
+done:
+	fclose(fp);
+
+	return ret;
+}
+
+int init_signal_handler(void)
+{
+	int signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT};
+	struct sigaction sa;
+	stack_t ss;
+
+	if (read_stack_limit())
+		return -1;
+
+	ss.ss_sp = malloc(SIGSTKSZ);
+	if (!ss.ss_sp) {
+		ERROR_GLIBC("malloc");
+		return -1;
+	}
+	ss.ss_size = SIGSTKSZ;
+	ss.ss_flags = 0;
+
+	if (sigaltstack(&ss, NULL) == -1) {
+		ERROR_GLIBC("sigaltstack");
+		return -1;
+	}
+
+	sa.sa_sigaction = signal_handler;
+	sigemptyset(&sa.sa_mask);
+
+	sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
+
+	for (int i = 0; i < ARRAY_SIZE(signals); i++) {
+		if (sigaction(signals[i], &sa, NULL) == -1) {
+			ERROR_GLIBC("sigaction");
+			return -1;
+		}
+	}
+
+	return 0;
+}
-- 
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