On Mon, Feb 10, 2020 at 10:00:47AM +0100, 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 you get some point. As you mentioned in the following reply, we need to adjust poisoning after this change. This looks like a trade off between two options. I don't have a strong preference. > >-- >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me