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

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Message-ID: <CAPcyv4h7dKE85EQ9jR1akXnT6PcG2M2g7YCCLqse=kKieP1H9w@mail.gmail.com>
Date:   Thu, 6 Feb 2020 18:19:46 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Baoquan He <bhe@...hat.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct
 instead of virtual address to pfn

On Thu, Feb 6, 2020 at 3:17 PM Wei Yang <richardw.yang@...ux.intel.com> wrote:
>
> memmap should be the physical address to page struct instead of virtual
> address to pfn.
>
> 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));

Yes, this looks obviously correct. This might be tripping up
makedumpfile. Do you see any practical effects of this bug? The kernel
mostly avoids ->section_mem_map in the vmemmap case and in the
!vmemmap case section_nr_to_pfn(section_nr) should always equal
start_pfn.