| Message ID | 20180515175124.1770-1-pasha.tatashin@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue 15-05-18 13:51:24, Pavel Tatashin wrote: > 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 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 > > 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> Thanks a lot! > --- > mm/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/Kconfig b/mm/Kconfig > index d5004d82a1d6..e14c01513bfd 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -636,6 +636,7 @@ config DEFERRED_STRUCT_PAGE_INIT > default n > depends on NO_BOOTMEM > depends on !FLATMEM > + 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 > -- > 2.17.0
On Tue, 15 May 2018 13:51:24 -0400 Pavel Tatashin <pasha.tatashin@oracle.com> wrote: > 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 exposed this problem, "my recent fix" isn't very useful. I changed this to identify c9e97a1997 ("mm: initialize pages on demand during boot"), yes? > > 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> And I added cc:stable.
> > My recent fix exposed this problem, > "my recent fix" isn't very useful. I changed this to identify > c9e97a1997 ("mm: initialize pages on demand during boot"), yes? Yes, thank you. Pavel
diff --git a/mm/Kconfig b/mm/Kconfig index d5004d82a1d6..e14c01513bfd 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -636,6 +636,7 @@ config DEFERRED_STRUCT_PAGE_INIT default n depends on NO_BOOTMEM depends on !FLATMEM + 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
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 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 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> --- mm/Kconfig | 1 + 1 file changed, 1 insertion(+)