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authorPavel Tatashin <pasha.tatashin@oracle.com>2018-05-18 16:09:13 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-26 08:48:55 +0200
commitec8d6e953ad179be174b59513d8392ef48f566d5 (patch)
treeee8109498a521c64e94fa1f7bef5eac7df27b8fa /mm/Kconfig
parent380efa6a71c5aba6dec2a1432a29644bb0b220a8 (diff)
mm: don't allow deferred pages with NEED_PER_CPU_KM
commit ab1e8d8960b68f54af42b6484b5950bd13a4054b upstream. It is unsafe to do virtual to physical translations before mm_init() is called if struct page is needed in order to determine the memory section number (see SECTION_IN_PAGE_FLAGS). This is because only in mm_init() we initialize struct pages for all the allocated memory when deferred struct pages are used. My recent fix in commit c9e97a1997 ("mm: initialize pages on demand during boot") exposed this problem, because it greatly reduced number of pages that are initialized before mm_init(), but the problem existed even before my fix, as Fengguang Wu found. Below is a more detailed explanation of the problem. We initialize struct pages in four places: 1. Early in boot a small set of struct pages is initialized to fill the first section, and lower zones. 2. During mm_init() we initialize "struct pages" for all the memory that is allocated, i.e reserved in memblock. 3. Using on-demand logic when pages are allocated after mm_init call (when memblock is finished) 4. After smp_init() when the rest free deferred pages are initialized. The problem occurs if we try to do va to phys translation of a memory between steps 1 and 2. Because we have not yet initialized struct pages for all the reserved pages, it is inherently unsafe to do va to phys if the translation itself requires access of "struct page" as in case of this combination: CONFIG_SPARSE && !CONFIG_SPARSE_VMEMMAP The following path exposes the problem: start_kernel() trap_init() setup_cpu_entry_areas() setup_cpu_entry_area(cpu) get_cpu_gdt_paddr(cpu) per_cpu_ptr_to_phys(addr) pcpu_addr_to_page(addr) virt_to_page(addr) pfn_to_page(__pa(addr) >> PAGE_SHIFT) We disable this path by not allowing NEED_PER_CPU_KM with deferred struct pages feature. The problems are discussed in these threads: http://lkml.kernel.org/r/20180418135300.inazvpxjxowogyge@wfg-t540p.sh.intel.com http://lkml.kernel.org/r/20180419013128.iurzouiqxvcnpbvz@wfg-t540p.sh.intel.com http://lkml.kernel.org/r/20180426202619.2768-1-pasha.tatashin@oracle.com Link: http://lkml.kernel.org/r/20180515175124.1770-1-pasha.tatashin@oracle.com Fixes: 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set") Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Steven Sistare <steven.sistare@oracle.com> Cc: Daniel Jordan <daniel.m.jordan@oracle.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Dennis Zhou <dennisszhou@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/Kconfig')
-rw-r--r--mm/Kconfig1
1 files changed, 1 insertions, 0 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index 97a4e06b15c0..5753f69b23f4 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -628,6 +628,7 @@ config DEFERRED_STRUCT_PAGE_INIT
default n
depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
depends on MEMORY_HOTPLUG
+ depends on !NEED_PER_CPU_KM
help
Ordinarily all struct pages are initialised during early boot in a
single thread. On very large machines this can take a considerable