Message-ID: <86ms317zk5.fsf@kernel.org>
Date: Mon, 29 Dec 2025 22:23:06 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Pratyush Yadav <pratyush@...nel.org>,  Mike Rapoport <rppt@...nel.org>,
  Andrew Morton <akpm@...ux-foundation.org>,  David Hildenbrand
 <david@...nel.org>,  Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,  "Liam
 R. Howlett" <Liam.Howlett@...cle.com>,  Vlastimil Babka <vbabka@...e.cz>,
  Suren Baghdasaryan <surenb@...gle.com>,  Michal Hocko <mhocko@...e.com>,
  Jonathan Corbet <corbet@....net>,  Thomas Gleixner <tglx@...utronix.de>,
  Ingo Molnar <mingo@...hat.com>,  Borislav Petkov <bp@...en8.de>,  Dave
 Hansen <dave.hansen@...ux.intel.com>,  x86@...nel.org,  "H. Peter Anvin"
 <hpa@...or.com>,  Muchun Song <muchun.song@...ux.dev>,  Oscar Salvador
 <osalvador@...e.de>,  Alexander Graf <graf@...zon.com>,  David Matlack
 <dmatlack@...gle.com>,  David Rientjes <rientjes@...gle.com>,  Jason
 Gunthorpe <jgg@...dia.com>,  Samiullah Khawaja <skhawaja@...gle.com>,
  Vipin Sharma <vipinsh@...gle.com>,  Zhu Yanjun <yanjun.zhu@...ux.dev>,
  linux-kernel@...r.kernel.org,  linux-mm@...ck.org,
  linux-doc@...r.kernel.org,  kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 03/10] liveupdate: do early initialization before
 hugepages are allocated

On Tue, Dec 23 2025, Pasha Tatashin wrote:

> On Sat, Dec 6, 2025 at 6:03 PM Pratyush Yadav <pratyush@...nel.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@...nel.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.

The function is used by liveupdate_flb_incoming_early() for
sanity-checking. Since we are getting rid of that, I can drop the
function too.

>
>> +
>>  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.

Sure, will do.

>
>> +
>>         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
>>

-- 
Regards,
Pratyush Yadav

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