On Tue, 24 Mar 2026 05:52:33 -0700 Breno Leitao <[email protected]> wrote:
> Right not is impossible to set early parameters in bootconfig, which > limits the usage of bootconfig to some critical parameters. > > Add bootconfig_apply_early_params() which walks all kernel.* keys in the > parsed XBC tree and calls do_early_param() for each one. It is called > from setup_boot_config() immediately after a successful xbc_init() on > the embedded data, which happens before parse_early_param() runs in > start_kernel(). > > This allows early options such as: > > kernel.mitigations = off > kernel.irqchip.gicv3_pseudo_nmi = 1 > > to be placed in the embedded bootconfig and take effect, without > requiring them to be on the kernel command line. > > Early options in initrd bootconfig are still silently ignored, as the > initrd is only available after the early param window has closed. > > Document this behaviour in both Kconfig and the admin guide. Thanks Breno, this makes things clearer. This looks good to me. Thanks, > > Signed-off-by: Breno Leitao <[email protected]> > --- > Documentation/admin-guide/bootconfig.rst | 4 ++ > init/Kconfig | 6 +++ > init/main.c | 67 > +++++++++++++++++++++++++++++++- > 3 files changed, 76 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/bootconfig.rst > b/Documentation/admin-guide/bootconfig.rst > index f712758472d5c..e820f33d3ad16 100644 > --- a/Documentation/admin-guide/bootconfig.rst > +++ b/Documentation/admin-guide/bootconfig.rst > @@ -169,6 +169,10 @@ Boot Kernel With a Boot Config > There are two options to boot the kernel with bootconfig: attaching the > bootconfig to the initrd image or embedding it in the kernel itself. > > +Early options (those registered with ``early_param()``) may only be > +specified in the embedded bootconfig, because the initrd is not yet > +available when early parameters are processed. > + > Attaching a Boot Config to Initrd > --------------------------------- > > diff --git a/init/Kconfig b/init/Kconfig > index 938fbe6a91e15..5e8057e73fe06 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1534,6 +1534,12 @@ config BOOT_CONFIG_EMBED > image. But if the system doesn't support initrd, this option will > help you by embedding a bootconfig file while building the kernel. > > + Unlike bootconfig attached to initrd, the embedded bootconfig also > + supports early options (those registered with early_param()). Any > + kernel.* key in the embedded bootconfig is applied before > + parse_early_param() runs. Early options in initrd bootconfig will > + not be applied. > + > If unsure, say N. > > config BOOT_CONFIG_EMBED_FILE > diff --git a/init/main.c b/init/main.c > index 453ac9dff2da0..eba42b2351d47 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -416,9 +416,63 @@ static int __init warn_bootconfig(char *str) > return 0; > } > > +/* > + * do_early_param() is defined later in this file but called from > + * bootconfig_apply_early_params() below, so we need a forward declaration. > + */ > +static int __init do_early_param(char *param, char *val, > + const char *unused, void *arg); > + > +/* > + * bootconfig_apply_early_params - dispatch kernel.* keys from the embedded > + * bootconfig as early_param() calls. > + * > + * early_param() handlers must run before most of the kernel initialises > + * (e.g. before the GIC driver reads irqchip.gicv3_pseudo_nmi). A bootconfig > + * attached to the initrd arrives too late for this because the initrd is not > + * mapped yet when early params are processed. The embedded bootconfig lives > + * in the kernel image itself (.init.data), so it is always reachable. > + * > + * This function is called from setup_boot_config() which runs in > + * start_kernel() before parse_early_param(), making the timing correct. > + */ > +static void __init bootconfig_apply_early_params(void) > +{ > + char val_buf[COMMAND_LINE_SIZE]; > + struct xbc_node *knode, *root; > + const char *val; > + > + root = xbc_find_node("kernel"); > + if (!root) > + return; > + > + /* > + * Keys that do not match any early_param() handler are silently > + * ignored — do_early_param() always returns 0. > + */ > + xbc_node_for_each_key_value(root, knode, val) { > + if (xbc_node_compose_key_after(root, knode, xbc_namebuf, > XBC_KEYLEN_MAX) < 0) > + continue; > + > + if (!val) { > + do_early_param(xbc_namebuf, NULL, NULL, NULL); > + continue; > + } > + > + /* > + * We need to copy const char *val to a char pointer, > + * which is what do_early_param() need, given it might > + * call strsep(), strtok() later. > + */ > + strscpy(val_buf, val, sizeof(val_buf)); > + do_early_param(xbc_namebuf, val_buf, NULL, NULL); > + } > +} > + > static void __init setup_boot_config(void) > { > static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata; > + bool using_embedded = false; > const char *msg, *data; > int pos, ret; > size_t size; > @@ -427,8 +481,17 @@ static void __init setup_boot_config(void) > /* Cut out the bootconfig data even if we have no bootconfig option */ > data = get_boot_config_from_initrd(&size); > /* If there is no bootconfig in initrd, try embedded one. */ > - if (!data) > + if (!data) { > data = xbc_get_embedded_bootconfig(&size); > + /* > + * Record that we are using the embedded config so that > + * bootconfig_apply_early_params() is called below. > + * When CONFIG_BOOT_CONFIG_EMBED is not set, > + * xbc_get_embedded_bootconfig() is a stub returning NULL, so > + * data is always NULL here and using_embedded stays false. > + */ > + using_embedded = data; > + } > > strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE); > err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL, > @@ -466,6 +529,8 @@ static void __init setup_boot_config(void) > } else { > xbc_get_info(&ret, NULL); > pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, > ret); > + if (using_embedded) > + bootconfig_apply_early_params(); > /* keys starting with "kernel." are passed via cmdline */ > extra_command_line = xbc_make_cmdline("kernel"); > /* Also, "init." keys are init arguments */ > > --- > base-commit: 785f0eb2f85decbe7c1ef9ae922931f0194ffc2e > change-id: 20260323-early_bootconfig-2efc4509af3d > > Best regards, > -- > Breno Leitao <[email protected]> > -- Masami Hiramatsu (Google) <[email protected]>
