Hi Evangelos,
On Tue, Dec 16, 2025 at 08:49:12AM +0000, Evangelos Petrongonas wrote:
> When `CONFIG_DEFERRED_STRUCT_PAGE_INIT` is enabled, struct page
No need for markup formatting in the changelog.
> initialization is deferred to parallel kthreads that run later
> in the boot process.
>
> During KHO restoration, `deserialize_bitmap()` writes metadata for
> each preserved memory region. However, if the struct page has not been
> initialized, this write targets uninitialized memory, potentially
> leading to errors like:
> ```
> BUG: unable to handle page fault for address: ...
> ```
>
> Fix this by introducing `kho_get_preserved_page()`, which ensures
> all struct pages in a preserved region are initialized by calling
> `init_deferred_page()` which is a no-op when deferred init is disabled
> or when the struct page is already initialized.
>
> Fixes: 8b66ed2c3f42 ("kho: mm: don't allow deferred struct page with KHO")
> Signed-off-by: Evangelos Petrongonas <[email protected]>
> ---
...
> +static struct page *__init kho_get_preserved_page(phys_addr_t phys,
> + unsigned int order)
> +{
> + unsigned long pfn = PHYS_PFN(phys);
> + int nid = early_pfn_to_nid(pfn);
> +
> + for (int i = 0; i < (1 << order); i++)
> + init_deferred_page(pfn + i, nid);
This will skip pages below node->first_deferred_pfn, we need to use
__init_page_from_nid() here.
> +
> + return pfn_to_page(pfn);
> +}
> +
> static void __init deserialize_bitmap(unsigned int order,
> struct khoser_mem_bitmap_ptr *elm)
> {
> @@ -449,7 +466,7 @@ static void __init deserialize_bitmap(unsigned int order,
> int sz = 1 << (order + PAGE_SHIFT);
> phys_addr_t phys =
> elm->phys_start + (bit << (order + PAGE_SHIFT));
> - struct page *page = phys_to_page(phys);
> + struct page *page = kho_get_preserved_page(phys, order);
I think it's better to initialize deferred struct pages later in
kho_restore_page. deserialize_bitmap() runs before SMP and it already does
heavy lifting of memblock_reserve()s. Delaying struct page initialization
until restore makes it at least run in parallel with other initialization
tasks.
I started to work on this just before plumbers and I have something
untested here:
https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kho/deferred-page/v0.1
> union kho_page_info info;
>
> memblock_reserve(phys, sz);
> --
> 2.43.0
>
>
>
>
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--
Sincerely yours,
Mike.
