From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

If user configures `kernel.key` in bootconfig, the 'key' is shown
in kernel cmdline (/proc/cmdline) and kernel boot parameter
handler associated with 'key' is invoked. However, since the
bootconfig does not support the parameter defined with early_param,
those keys are shown in '/proc/cmdline' but not handled by kernel.

This could easily mislead users who expected to be able to specify
early parameters via the boot configuration, leading them to wonder
why it doesn't work.

Let's skip printing out early params to cmdline buffer, and warn
if there is such parameters in bootconfig.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 init/main.c |   30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/init/main.c b/init/main.c
index 1cb395dd94e4..095c497ea2df 100644
--- a/init/main.c
+++ b/init/main.c
@@ -324,10 +324,21 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 
 static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata;
 
+static bool __init is_early_param(const char *param)
+{
+	const struct obs_kernel_param *p;
+
+	for (p = __setup_start; p < __setup_end; p++) {
+		if (p->early && parameq(param, p->str))
+			return true;
+	}
+	return false;
+}
+
 #define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
 
 static int __init xbc_snprint_cmdline(char *buf, size_t size,
-				      struct xbc_node *root)
+				      struct xbc_node *root, bool is_kernel)
 {
 	struct xbc_node *knode, *vnode;
 	char *end = buf + size;
@@ -340,6 +351,13 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
 		if (ret < 0)
 			return ret;
 
+		/* We will skip early params because it is not applied. */
+		if (is_kernel && is_early_param(xbc_namebuf)) {
+			pr_warn_once("early_param(e.g. %s.%s) is not passed to cmdline from bootconfig\n",
+				     xbc_node_get_data(root), xbc_namebuf);
+			continue;
+		}
+
 		vnode = xbc_node_get_child(knode);
 		if (!vnode) {
 			ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf);
@@ -368,7 +386,7 @@ static int __init xbc_snprint_cmdline(char *buf, size_t size,
 #undef rest
 
 /* Make an extra command line under given key word */
-static char * __init xbc_make_cmdline(const char *key)
+static char * __init xbc_make_cmdline(const char *key, bool is_kernel)
 {
 	struct xbc_node *root;
 	char *new_cmdline;
@@ -379,7 +397,7 @@ static char * __init xbc_make_cmdline(const char *key)
 		return NULL;
 
 	/* Count required buffer size */
-	len = xbc_snprint_cmdline(NULL, 0, root);
+	len = xbc_snprint_cmdline(NULL, 0, root, is_kernel);
 	if (len <= 0)
 		return NULL;
 
@@ -389,7 +407,7 @@ static char * __init xbc_make_cmdline(const char *key)
 		return NULL;
 	}
 
-	ret = xbc_snprint_cmdline(new_cmdline, len + 1, root);
+	ret = xbc_snprint_cmdline(new_cmdline, len + 1, root, is_kernel);
 	if (ret < 0 || ret > len) {
 		pr_err("Failed to print extra kernel cmdline.\n");
 		memblock_free(new_cmdline, len + 1);
@@ -465,9 +483,9 @@ static void __init setup_boot_config(void)
 		xbc_get_info(&ret, NULL);
 		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
 		/* keys starting with "kernel." are passed via cmdline */
-		extra_command_line = xbc_make_cmdline("kernel");
+		extra_command_line = xbc_make_cmdline("kernel", true);
 		/* Also, "init." keys are init arguments */
-		extra_init_args = xbc_make_cmdline("init");
+		extra_init_args = xbc_make_cmdline("init", false);
 	}
 	return;
 }

On Wed, Apr 01, 2026 at 11:02:55PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> If user configures `kernel.key` in bootconfig, the 'key' is shown
> in kernel cmdline (/proc/cmdline) and kernel boot parameter
> handler associated with 'key' is invoked. However, since the
> bootconfig does not support the parameter defined with early_param,
> those keys are shown in '/proc/cmdline' but not handled by kernel.
> 
> This could easily mislead users who expected to be able to specify
> early parameters via the boot configuration, leading them to wonder
> why it doesn't work.
> 
> Let's skip printing out early params to cmdline buffer, and warn
> if there is such parameters in bootconfig.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Reviewed-by: Breno Leitao <leitao@debian.org>

> +static bool __init is_early_param(const char *param)
> +{
> +	const struct obs_kernel_param *p;
> +
> +	for (p = __setup_start; p < __setup_end; p++) {
> +		if (p->early && parameq(param, p->str))
> +			return true;
> +	}

nit: I don't think you need the parenthesis ({) for the ifs in here.