On 10.02.20 10:00, David Hildenbrand wrote:
> On 10.02.20 01:50, Wei Yang wrote:
>> memmap should be the address to page struct instead of address to pfn.
>>
>
> "mm/sparsemem: fix wrong address in ms->section_mem_map with sub-sections
>
> We want to store the address of the memmap, not the address of the first
> pfn.
>
> E.g., we can have both (boot) system memory and devmem residing in a
> single section. Once we hot-add the devmem part, the address stored in
> ms->section_mem_map would be wrong, and kdump would not be able to
> dump the right memory.
> "
>
> ? See below
>
>> As mentioned by David, if system memory and devmem sit within a
>> section, the mismatch address would lead kdump to dump unexpected
>> memory.
>>
>> Since sub-section only works for SPARSEMEM_VMEMMAP, pfn_to_page() is
>> valid to get the page struct address at this point.
>>
>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
>> CC: Dan Williams <dan.j.williams@xxxxxxxxx>
>> CC: David Hildenbrand <david@xxxxxxxxxx>
>> CC: Baoquan He <bhe@xxxxxxxxxx>
>>
>> ---
>> v2:
>> * adjust comment to mention the mismatch data would affect kdump
>>
>> ---
>> mm/sparse.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 586d85662978..4862ec2cfbc0 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -887,7 +887,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>>
>> /* Align memmap to section boundary in the subsection case */
>> if (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));
>
> I think this whole code should be reworked.
>
> Callee returns a pointer. Caller: Nah, I know it better.
>
> Just nasty.
>
>
> Can we do something like this instead:
>
>
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 200aef686722..c5091feef29e 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -266,5 +266,5 @@ struct page * __meminit
> __populate_section_memmap(unsigned long pfn,
> if (vmemmap_populate(start, end, nid, altmap))
> return NULL;
>
> - return pfn_to_page(pfn);
> + return pfn_to_page(SECTION_ALIGN_DOWN(pfn));
> }
> diff --git a/mm/sparse.c b/mm/sparse.c
> index c184b69460b7..21902d7931e4 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -788,6 +788,10 @@ static void section_deactivate(unsigned long pfn,
> unsigned long nr_pages,
> depopulate_section_memmap(pfn, nr_pages, altmap);
> }
>
> +/*
> + * Returns the memmap of the first pfn of the section (not of
> + * sub-sections).
> + */
> static struct page * __meminit section_activate(int nid, unsigned long pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap)
> {
> @@ -882,9 +886,6 @@ int __meminit sparse_add_section(int nid, unsigned
> long start_pfn,
> set_section_nid(section_nr, nid);
> section_mark_present(ms);
>
> - /* Align memmap to section boundary in the subsection case */
> - if (section_nr_to_pfn(section_nr) != start_pfn)
> - memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr));
> sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);
>
> return 0;
>
>
> Untested, of course :)
>
I think the following would be needed as well with Wei's fix:
@@ -876,15 +880,13 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
* Poison uninitialized struct pages in order to catch invalid flags
* combinations.
*/
- page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages);
+ page_init_poison(memmap + start_pfn - SECTION_ALIGN_DOWN(start_pfn),
+ sizeof(struct page) * nr_pages);
ms = __nr_to_section(section_nr);
Or we can simply move the poisoning behind sparse_init_one_section().
--
Thanks,
David / dhildenb
