[PATCH v6 0/7] fixes of TLB batching races

Nadav Amit
2017-08-02T07:34:29Z

It turns out that Linux TLB batching mechanism suffers from various races.
Races that are caused due to batching during reclamation were recently
handled by Mel and this patch-set deals with others. The more fundamental
issue is that concurrent updates of the page-tables allow for TLB flushes
to be batched on one core, while another core changes the page-tables.
This other core may assume a PTE change does not require a flush based on
the updated PTE value, while it is unaware that TLB flushes are still
pending.

This behavior affects KSM (which may result in memory corruption) and
MADV_FREE and MADV_DONTNEED (which may result in incorrect behavior). A
proof-of-concept can easily produce the wrong behavior of MADV_DONTNEED.
Memory corruption in KSM is harder to produce in practice, but was observed
by hacking the kernel and adding a delay before flushing and replacing the
KSM page.

Finally, there is also one memory barrier missing, which may affect
architectures with weak memory model.

v5 -> v6:
* Combining with Minchan Kim's patch set, adding ack's (Andrew)
* Minor: missing header, typos (Nadav)
* Renaming arch_generic_tlb_finish_mmu (Mel)

Michnan's v1 -> v2 (combined):
* TLB batching API separation core part from arch specific one (Mel)
* introduce mm_tlb_flush_nested (Mel)

v4 -> v5:
* Fixing embarrassing build mistake (0day)

v3 -> v4:
* Change function names to indicate they inc/dec and not set/clear
(Sergey)
* Avoid additional barriers, and instead revert the patch that accessed
mm_tlb_flush_pending without a lock (Mel)

v2 -> v3:
* Do not init tlb_flush_pending if it is not defined without (Sergey)
* Internalize memory barriers to mm_tlb_flush_pending (Minchan)

v1 -> v2:
* Explain the implications of the implications of the race (Andrew)
* Mark the patch that address the race as stable (Andrew)
* Add another patch to clean the use of barriers (Andrew)

Minchan Kim (4):
mm: refactoring TLB gathering API
mm: make tlb_flush_pending global
mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem
mm: fix KSM data corruption

Nadav Amit (3):
mm: migrate: prevent racy access to tlb_flush_pending
mm: migrate: fix barriers around tlb_flush_pending
Revert "mm: numa: defer TLB flush for THP migration as long as
possible"

arch/arm/include/asm/tlb.h | 11 ++++++--
arch/ia64/include/asm/tlb.h | 8 ++++--
arch/s390/include/asm/tlb.h | 17 +++++++-----
arch/sh/include/asm/tlb.h | 8 +++---
arch/um/include/asm/tlb.h | 13 ++++++---
fs/proc/task_mmu.c | 7 +++--
include/asm-generic/tlb.h | 7 ++---
include/linux/mm_types.h | 64 +++++++++++++++++++++++++++------------------
kernel/fork.c | 2 +-
mm/debug.c | 4 +--
mm/huge_memory.c | 7 +++++
mm/ksm.c | 3 ++-
mm/memory.c | 41 ++++++++++++++++++++++++-----
mm/migrate.c | 6 -----
mm/mprotect.c | 4 +--
15 files changed, 135 insertions(+), 67 deletions(-)

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2.11.0