On Mon, 30 Mar 2026 08:04:23 -0700 Breno Leitao <[email protected]> wrote:
> On Mon, Mar 30, 2026 at 06:15:17AM -0700, Breno Leitao wrote: > > On Fri, Mar 27, 2026 at 10:37:44PM +0900, Masami Hiramatsu wrote: > > > On Fri, 27 Mar 2026 03:06:41 -0700 > > > Breno Leitao <[email protected]> wrote: > > > > > > > To fix this, we need to change setup_arch() for each architecture so > > > > > that it calls this bootconfig_apply_early_params(). > > > > > > > > Could we instead integrate this into parse_early_param() itself? That > > > > approach would avoid the need to modify each architecture individually. > > > > > > Ah, indeed. > > > > I investigated integrating bootconfig into parse_early_param() and hit a > > blocker: xbc_init() and xbc_make_cmdline() depend on memblock_alloc(), but > > on > > most architectures (x86, arm64, arm, s390, riscv) parse_early_param() is > > called > > from setup_arch() _before_ memblock is initialized. > > That said, I'd like to propose a simpler approach as a first step: > > 1) Keep calling bootconfig_apply_early_params() from setup_boot_config(). > This is the least intrusive approach and expands bootconfig support to > additional early boot parameters. > > 2) Document that architecture-specific early parameters might be ignored. > If a parameter is consumed early enough (during setup_arch()), it will > not see the bootconfig value. We have to carefully do this because what parameter is arch specific or not depends on architecture and undocumented. How about introducing a new Kconfig, which supports early params by embedded bootconfig? > > 3) Ensure that early bootconfig parameters don't overwrite the boot command > line. For example, if the boot command line has foo=bar and bootconfig > later has foo=baz, the command line value should take precedence. > This prevents early boot code (in setup_arch()) from seeing a parameter > value that will be changed later. OK, this also needs to be considered. Currently we just pass the bootconfig parameters right before bootloader given parameters as "extra_command_line" if "bootconfig" in cmdline or CONFIG_BOOT_CONFIG_FORCE=y. [boot_config(.kernel)]<command_line>[ -- [boot_config(.init)][init_command_line]] This is currently expected behavior. The bootconfig parameters are expected to be overridden by command_line or command_line are appended. If we change this for early params, we also should change the expected output of /proc/cmdline too. I think we have 2 options; - As before, we expect the parameters provided by the boot configuration to be processed first and then overridden later by the command line. Or, - ignore all parameters which is given from the command line, this also updates existing setup_boot_config() (means xbc_snprint_cmdline() ). Anyway, this behavior change will also be a bit critical... We have to announce it. > > > If that is OK, that is what I have right now: Let me comment on it. > diff --git a/Documentation/admin-guide/bootconfig.rst > b/Documentation/admin-guide/bootconfig.rst > index f712758472d5c..6ed852a0c66d8 100644 > --- a/Documentation/admin-guide/bootconfig.rst > +++ b/Documentation/admin-guide/bootconfig.rst > @@ -169,6 +169,15 @@ 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. > + > +Note that embedded bootconfig is parsed after ``setup_arch()``, so > +early options that are consumed during architecture initialization > +(e.g., ``mem=``, ``memmap=``, ``earlycon``, ``noapic``, ``nolapic``, > +``acpi=``, ``numa=``, ``iommu=``) may not take effect from bootconfig. > + This is easy to explain, but it's quite troublesome for users to determine which parameters are unavailable. Currently we can identify it by `git grep early_param -- arch/${ARCH}`. But it is setup in setup_arch() we need to track the source code. (Or ask AI :)) > Attaching a Boot Config to Initrd > --------------------------------- > > diff --git a/init/Kconfig b/init/Kconfig > index 7484cd703bc1a..34adcc1feb9b6 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1525,6 +1525,16 @@ 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. Early options consumed during setup_arch() (e.g. > + mem=, memmap=, earlycon, noapic, acpi=, numa=, iommu=) may not > + take effect. If the same early option > + appears in both bootconfig and the kernel command line, the > + command line value takes precedence. > + As a compromise, how about making this a separate Kconfig? config BOOT_CONFIG_EMBED_EARLY_PARAM bool "Support early_params in embedded bootconfig" and afterwards, we can introduce depends on ARCH_BOOT_CONFIG_EMBED_EARLY_PARAM Thank you, -- Masami Hiramatsu (Google) <[email protected]>
