Re: [RFC PATCH 03/10] liveupdate: do early initialization before hugepages are allocated

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Sat, Dec 6, 2025 at 6:03 PM Pratyush Yadav <pratyush@kernel.org> wrote:
>
> To support hugepage preservation using LUO, the hugetlb subsystem needs
> to get liveupdate data when it allocates the hugepages to find out how
> many pages are coming from live update.
>
> Move early LUO init from early_initcall to mm_core_init(). This is where
> gigantic hugepages are allocated on ARM64. On x86, they are allocated in
> setup_arch(), so have a call there as well. Keep track of whether the
> function was already called to avoid double-init.
>
> liveupdate_early_init() only gets the KHO subtree and validates the data
> to ensure it is valid and understood. These are read-only operations and
> do not need much from the system, so it is safe to call early in boot.
>
> Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
> ---
>  arch/x86/kernel/setup.c          |  7 +++++++
>  include/linux/liveupdate.h       |  6 ++++++
>  kernel/liveupdate/luo_core.c     | 30 ++++++++++++++++++++++++++----
>  kernel/liveupdate/luo_internal.h |  2 ++
>  mm/mm_init.c                     |  7 +++++++
>  5 files changed, 48 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 9bf00287c408..e2ec779afc2c 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -26,6 +26,7 @@
>  #include <linux/tboot.h>
>  #include <linux/usb/xhci-dbgp.h>
>  #include <linux/vmalloc.h>
> +#include <linux/liveupdate.h>
>
>  #include <uapi/linux/mount.h>
>
> @@ -1216,6 +1217,12 @@ void __init setup_arch(char **cmdline_p)
>
>         kho_memory_init();
>
> +       /*
> +        * Hugepages might be preserved from a liveupdate. Make sure it is
> +        * initialized so hugetlb can query its state.
> +        */
> +       liveupdate_early_init();
> +
>         if (boot_cpu_has(X86_FEATURE_GBPAGES)) {
>                 hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
>                 hugetlb_bootmem_alloc();
> diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
> index ed81e7b31a9f..78e8c529e4e7 100644
> --- a/include/linux/liveupdate.h
> +++ b/include/linux/liveupdate.h
> @@ -214,6 +214,8 @@ struct liveupdate_flb {
>
>  #ifdef CONFIG_LIVEUPDATE
>
> +void __init liveupdate_early_init(void);
> +
>  /* Return true if live update orchestrator is enabled */
>  bool liveupdate_enabled(void);
>
> @@ -233,6 +235,10 @@ int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp);
>
>  #else /* CONFIG_LIVEUPDATE */
>
> +static inline void liveupdate_early_init(void)
> +{
> +}
> +
>  static inline bool liveupdate_enabled(void)
>  {
>         return false;
> diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
> index 7a9ef16b37d8..2c740ecad8e6 100644
> --- a/kernel/liveupdate/luo_core.c
> +++ b/kernel/liveupdate/luo_core.c
> @@ -69,6 +69,13 @@ static struct {
>         u64 liveupdate_num;
>  } luo_global;
>
> +static bool __luo_early_initialized __initdata;
> +
> +bool __init luo_early_initialized(void)
> +{
> +       return __luo_early_initialized;
> +}

I think the above is not needed, both the global variable, and a new function.

> +
>  static int __init early_liveupdate_param(char *buf)
>  {
>         return kstrtobool(buf, &luo_global.enabled);
> @@ -133,20 +140,35 @@ static int __init luo_early_startup(void)
>         return err;
>  }
>
> -static int __init liveupdate_early_init(void)
> +/*
> + * This should only be called after KHO FDT is known. It gets the LUO subtree
> + * and does initial validation, making early boot read-only access possible.
> + */
> +void __init liveupdate_early_init(void)
>  {
>         int err;
>
> +       /*
> +        * HugeTLB needs LUO to be initialized early in boot, before gigantic
> +        * hugepages are allocated. On x86, that happens in setup_arch(), but on
> +        * ARM64 (and other architectures) that happens in mm_core_init().
> +        *
> +        * Since the code in mm_core_init() is shared between all architectures,
> +        * this can lead to the init being called twice. Skip if initialization
> +        * was already done.
> +        */
> +       if (__luo_early_initialized)
> +               return;
> +
> +       __luo_early_initialized = true;

Please, make __luo_early_initialized static local.

> +
>         err = luo_early_startup();
>         if (err) {
>                 luo_global.enabled = false;
>                 luo_restore_fail("The incoming tree failed to initialize properly [%pe], disabling live update\n",
>                                  ERR_PTR(err));
>         }
> -
> -       return err;
>  }
> -early_initcall(liveupdate_early_init);
>
>  /* Called during boot to create outgoing LUO fdt tree */
>  static int __init luo_fdt_setup(void)
> diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
> index 6115d6a4054d..171c54af7b38 100644
> --- a/kernel/liveupdate/luo_internal.h
> +++ b/kernel/liveupdate/luo_internal.h
> @@ -114,6 +114,8 @@ int __init luo_flb_setup_outgoing(void *fdt);
>  int __init luo_flb_setup_incoming(void *fdt);
>  void luo_flb_serialize(void);
>
> +bool __init luo_early_initialized(void);
> +
>  #ifdef CONFIG_LIVEUPDATE_TEST
>  void liveupdate_test_register(struct liveupdate_file_handler *fh);
>  void liveupdate_test_unregister(struct liveupdate_file_handler *fh);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 93cec06c1c8a..9a5b06a93622 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -31,6 +31,7 @@
>  #include <linux/execmem.h>
>  #include <linux/vmstat.h>
>  #include <linux/kexec_handover.h>
> +#include <linux/liveupdate.h>
>  #include <linux/hugetlb.h>
>  #include "internal.h"
>  #include "slab.h"
> @@ -2681,6 +2682,12 @@ void __init mm_core_init(void)
>         arch_mm_preinit();
>
>         kho_memory_init();
> +       /*
> +        * Hugepages might be preserved from a liveupdate. Make sure it is
> +        * initialized so hugetlb can query its state.
> +        */
> +       liveupdate_early_init();
> +
>         hugetlb_bootmem_alloc();
>
>         /* Initializations relying on SMP setup */
> --
> 2.43.0
>