linux-kernel - Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn

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Date:   Fri, 7 Feb 2020 12:11:34 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     akpm@...ux-foundation.org, osalvador@...e.de,
        dan.j.williams@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, david@...hat.com
Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct
 instead of virtual address to pfn

On 02/07/20 at 07:16am, Wei Yang wrote:
> memmap should be the physical address to page struct instead of virtual
> address to pfn.

Maybe not, memmap stores a virtual address.

> 
> Since we call this only for SPARSEMEM_VMEMMAP, pfn_to_page() is valid at
> this point.
> 
> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> CC: Dan Williams <dan.j.williams@...el.com>
> ---
>  mm/sparse.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index b5da121bdd6e..56816f653588 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -888,7 +888,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	/* Align memmap to section boundary in the subsection case */
>  	if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
>  		section_nr_to_pfn(section_nr) != start_pfn)
> -		memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr));
> +		memmap = pfn_to_page(section_nr_to_pfn(section_nr));

With Dan's confirmation, sub-section is only valid in vmemmap case. I
think the old if (section_nr_to_pfn(section_nr) != start_pfn) is enough
to filter out non vmemmap case. So only below code is good:

 +		memmap = pfn_to_page(section_nr_to_pfn(section_nr));

>  	sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
>  
>  	return 0;
> -- 
> 2.17.1
>