[PATCH v7 2/3] kho: fix deferred init of kho scratch

[Michał Cłapiński]

On Wed, Mar 18, 2026 at 4:10 PM Zi Yan <ziy at nvidia.com> wrote:
>
> On 17 Mar 2026, at 10:15, Michal Clapinski wrote:
>
> > Currently, if DEFERRED is enabled, kho_release_scratch will initialize
> > the struct pages and set migratetype of kho scratch. Unless the whole
> > scratch fit below first_deferred_pfn, some of that will be overwritten
> > either by deferred_init_pages or memmap_init_reserved_pages.
> >
> > To fix it, I modified kho_release_scratch to only set the migratetype
> > on already initialized pages. Then, modified init_pageblock_migratetype
> > to set the migratetype to CMA if the page is located inside scratch.
> >
> > Signed-off-by: Michal Clapinski <mclapinski at google.com>
> > ---
> >  include/linux/memblock.h           |  2 --
> >  kernel/liveupdate/kexec_handover.c | 10 ++++++----
> >  mm/memblock.c                      | 22 ----------------------
> >  mm/page_alloc.c                    |  7 +++++++
> >  4 files changed, 13 insertions(+), 28 deletions(-)
> >
>
> <snip>
>
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index ee81f5c67c18..5ca078dde61d 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -55,6 +55,7 @@
> >  #include <linux/cacheinfo.h>
> >  #include <linux/pgalloc_tag.h>
> >  #include <linux/mmzone_lock.h>
> > +#include <linux/kexec_handover.h>
> >  #include <asm/div64.h>
> >  #include "internal.h"
> >  #include "shuffle.h"
> > @@ -549,6 +550,12 @@ void __meminit init_pageblock_migratetype(struct page *page,
> >                    migratetype < MIGRATE_PCPTYPES))
> >               migratetype = MIGRATE_UNMOVABLE;
> >
> > +     /*
> > +      * Mark KHO scratch as CMA so no unmovable allocations are made there.
> > +      */
> > +     if (unlikely(kho_scratch_overlap(page_to_phys(page), PAGE_SIZE)))
> > +             migratetype = MIGRATE_CMA;
> > +
>
> If this is only for deferred init code, why not put it in deferred_free_pages()?
> Otherwise, all init_pageblock_migratetype() callers need to pay the penalty
> of traversing kho_scratch array.

Because reserve_bootmem_region() doesn't call deferred_free_pages().
So I would also have to modify it.

And the early initialization won't pay the penalty of traversing the
kho_scratch array, since then kho_scratch is NULL.

> >       flags = migratetype;
> >
> >  #ifdef CONFIG_MEMORY_ISOLATION
>
>
>
> Best Regards,
> Yan, Zi