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b=levK1FBGpysdmLQOMdTo0qNcTtB0s7RX0y4zTPIEcUboIVYrPZOuGFhUa6bo1W/fU Pkek4dlakV/QjzQcJYVYOoV/eRv457Rq1NkDVdejTSJwEFwt+UxkCc1PWpnmJO80LY OL/lhVJqjN+0W60eOuJJgkdiDtXm+r/RhggI5M/bwpZsNd03GHw3XpSEsQwOWig4A3 gBVT33D3IxuFbVGr9FbnmTvRhBd1ELZKiTNHPGscDsPTuppGV24iZQyq64K8sk0rYj SIdtnuzpZ8U/M8KggrJqRCjAmPMIXZl7O824bvxFkO6Vj/GpuSPgGhJSrKDsxcmuzD JbumRAVzfWYHg== Date: Tue, 16 Dec 2025 13:57:19 +0200 From: Mike Rapoport To: Evangelos Petrongonas Cc: Pasha Tatashin , Pratyush Yadav , Alexander Graf , Andrew Morton , Jason Miu , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, nh-open-source@amazon.com Subject: Re: [PATCH] kho: add support for deferred struct page init Message-ID: References: <20251216084913.86342-1-epetron@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251216084913.86342-1-epetron@amazon.de> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: E3E1918000B X-Stat-Signature: iu34kmtqaygg57h68gqu6n4qjhhf5y43 X-Rspam-User: X-HE-Tag: 1765886247-740184 X-HE-Meta: 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 8hCBq/8S xNkGl7iFhIKt1VqeWHn7qyU0kiu0IYBxTjCXu7eGrjX5I8enZA6kcP+UyjEql82mj8ZhjwqDbzHsj3ZhV1fDPZiSvbCMtVvN/HcRsADHqFC5jMlgzCZVJh1NMaC+qLKIRkQJiw8dPUDcvaauUpqvy01lpY69HCwGpCrUWJvUg5sWRq7TiR4COan5F35XGc8Dbjww5TNSe2Pf4ltJP2Y6RuiH11ejU+pLICjh6M5MoLbatZm0V+re7mxDmTm6re4mdv1fm0gNEZBzkQVJdNudQIErLog== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > --- ... > +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 > > > > > Amazon Web Services Development Center Germany GmbH > Tamara-Danz-Str. 13 > 10243 Berlin > Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger > Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B > Sitz: Berlin > Ust-ID: DE 365 538 597 > -- Sincerely yours, Mike.