Messages in this thread | | | Subject | Re: [PATCH] mm/sparse: Fix flags overlap in section_mem_map | From | David Hildenbrand <> | Date | Tue, 27 Apr 2021 11:05:17 +0200 |
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On 27.04.21 10:30, Wang Wensheng wrote: > The section_mem_map member of struct mem_section stores some flags and > the address of struct page array of the mem_section. > > Additionally the node id of the mem_section is stored during early boot, > where the struct page array has not been allocated. In other words, the > higher bits of section_mem_map are used for two purpose, and the node id > should be clear properly after the early boot. > > Currently the node id field is overlapped with the flag field and cannot > be clear properly. That overlapped bits would then be treated as > mem_section flags and may lead to unexpected side effects. > > Define SECTION_NID_SHIFT using order_base_2 to ensure that the node id > field always locates after flags field. That's why the overlap occurs - > forgetting to increase SECTION_NID_SHIFT when adding new mem_section > flag. > > Fixes: 326e1b8f83a4 ("mm/sparsemem: introduce a SECTION_IS_EARLY flag") > Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com> > --- > include/linux/mmzone.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 47946ce..b01694d 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1325,7 +1325,7 @@ extern size_t mem_section_usage_size(void); > #define SECTION_TAINT_ZONE_DEVICE (1UL<<4) > #define SECTION_MAP_LAST_BIT (1UL<<5) > #define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1)) > -#define SECTION_NID_SHIFT 3 > +#define SECTION_NID_SHIFT order_base_2(SECTION_MAP_LAST_BIT) > > static inline struct page *__section_mem_map_addr(struct mem_section *section) > { >
Well, all sections around during boot that have an early NID are early ... so it's not an issue with SECTION_IS_EARLY, no? I mean, it's ugly, but not broken.
But it's an issue with SECTION_TAINT_ZONE_DEVICE, AFAIKT. sparse_init_one_section() would leave the bit set if the nid happens to have that bit set (e.g., node 2,3). It's semi-broken then, because we force all pfn_to_online_page() through the slow path.
That whole section flag setting code is fragile.
-- Thanks,
David / dhildenb
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