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Pavel Tatashin ab1e8d8960 mm: don't allow deferred pages with NEED_PER_CPU_KM 
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: 3a80a7fa79 ("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>
2018-05-18 17:17:12 -07:00
arch powerpc fixes for 4.17 #6 2018-05-18 10:24:03 -07:00
block blk-mq: fix sysfs inflight counter 2018-04-26 09:02:01 -06:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto crypto: drbg - set freed buffers to NULL 2018-04-21 00:57:00 +08:00
Documentation powerpc fixes for 4.17 #6 2018-05-18 10:24:03 -07:00
drivers powerpc fixes for 4.17 #6 2018-05-18 10:24:03 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs proc: do not access cmdline nor environ from file-backed areas 2018-05-17 09:27:47 -07:00
include include/linux/mm.h: add new inline function vmf_error() 2018-05-18 17:17:12 -07:00
init init: fix false positives in W+X checking 2018-05-11 17:28:45 -07:00
ipc ipc/shm: fix use-after-free of shm file via remap_file_pages() 2018-04-13 17:10:27 -07:00
kernel Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-05-13 10:53:08 -07:00
lib radix tree: fix multi-order iteration race 2018-05-18 17:17:12 -07:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
mm mm: don't allow deferred pages with NEED_PER_CPU_KM 2018-05-18 17:17:12 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-11 14:14:46 -07:00
samples bpf: sockmap sample use clang flag, -target bpf 2018-04-23 23:42:21 +02:00
scripts scripts/faddr2line: fix error when addr2line output contains discriminator 2018-05-11 17:28:45 -07:00
security selinux/stable-4.17 PR 20180516 2018-05-17 10:02:19 -07:00
sound ALSA: usb-audio: Use Class Specific EP for UAC3 devices. 2018-05-15 07:29:10 +02:00
tools radix tree test suite: multi-order iteration race 2018-05-18 17:17:12 -07:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM: arm/arm64: VGIC/ITS save/restore: protect kvm_read_guest() calls 2018-05-15 13:36:53 +02:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge candidates for 4.17 merge window 2018-04-06 17:35:43 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: add Q: entry to kselftest for patchwork project 2018-05-18 17:17:12 -07:00
Makefile Linux 4.17-rc5 2018-05-13 16:15:17 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.