linux-kernel - Re: [PATCH 0/8] implement "memmap on memory" feature on s390

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Date:   Tue, 21 Nov 2023 14:21:26 +0100
From:   Sumanth Korikkar <sumanthk@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/8] implement "memmap on memory" feature on s390

On Tue, Nov 21, 2023 at 02:13:22PM +0100, Sumanth Korikkar wrote:
> Approach 2:
> ===========
> Shouldnt kasan zero shadow mapping performed first before
> accessing/initializing memmap via page_init_poisining()?  If that is
> true, then it is a problem for all architectures and should could be
> fixed like:
> 
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 7a5fc89a8652..eb3975740537 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1093,6 +1093,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
>  	if (ret)
>  		return ret;
> 
> +	page_init_poison(pfn_to_page(pfn), sizeof(struct page) * nr_pages);
>  	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
> 
>  	for (i = 0; i < nr_pages; i++)
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 77d91e565045..4ddf53f52075 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -906,8 +906,11 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	/*
>  	 * Poison uninitialized struct pages in order to catch invalid flags
>  	 * combinations.
> +	 * For altmap, do this later when onlining the memory, as it might
> +	 * not be accessible at this point.
>  	 */
> -	page_init_poison(memmap, sizeof(struct page) * nr_pages);
> +	if (!altmap)
> +		page_init_poison(memmap, sizeof(struct page) * nr_pages);
> 
>  	ms = __nr_to_section(section_nr);
>  	set_section_nid(section_nr, nid);
> 
> 
> 
> Also, if this approach is taken, should page_init_poison() be performed
> with cond_resched() as mentioned in commit d33695b16a9f
> ("mm/memory_hotplug: poison memmap in remove_pfn_range_from_zone()") ?

Sorry, wrong commit id.

should page_init_poison() be performed with cond_resched() as mentioned in
Commit b7e3debdd040 ("mm/memory_hotplug.c: fix false softlockup
during pfn range removal") ?

Thanks
> 
> Opinions?
> 
> Thank you