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Subject[PATCH 0/3] mmu_notifier: Allow to manage CPU external TLBs
Date
Hi,

here is a patch-set to extend the mmu_notifiers in the Linux
kernel to allow managing CPU external TLBs. Those TLBs may
be implemented in IOMMUs or any other external device, e.g.
ATS/PRI capable PCI devices.

The problem with managing these TLBs are the semantics of
the invalidate_range_start/end call-backs currently
available. Currently the subsystem using mmu_notifiers has
to guarantee that no new TLB entries are established between
invalidate_range_start/end. Furthermore the
invalidate_range_start() function is called when all pages
are still mapped and invalidate_range_end() when the pages
are unmapped an already freed.

So both call-backs can't be used to safely flush any non-CPU
TLB because _start() is called too early and _end() too
late.

In the AMD IOMMUv2 driver this is currently implemented by
assigning an empty page-table to the external device between
_start() and _end(). But as tests have shown this doesn't
work as external devices don't re-fault infinitly but enter
a failure state after some time.

Next problem with this solution is that it causes an
interrupt storm for IO page faults to be handled when an
empty page-table is assigned.

To solve this situation I wrote a patch-set to introduce a
new notifier call-back: mmu_notifer_invalidate_range(). This
notifier lifts the strict requirements that no new
references are taken in the range between _start() and
_end(). When the subsystem can't guarantee that any new
references are taken is has to provide the
invalidate_range() call-back to clear any new references in
there.

It is called between invalidate_range_start() and _end()
every time the VMM has to wipe out any references to a
couple of pages. This are usually the places where the CPU
TLBs are flushed too and where its important that this
happens before invalidate_range_end() is called.

Any comments and review appreciated!

Thanks,

Joerg

Joerg Roedel (3):
mmu_notifier: Add mmu_notifier_invalidate_range()
mmu_notifier: Call mmu_notifier_invalidate_range() from VMM
mmu_notifier: Add the call-back for mmu_notifier_invalidate_range()

include/linux/mmu_notifier.h | 66 ++++++++++++++++++++++++++++++++++++++++----
kernel/events/uprobes.c | 2 +-
mm/fremap.c | 2 +-
mm/huge_memory.c | 9 +++---
mm/hugetlb.c | 7 ++++-
mm/ksm.c | 4 +--
mm/memory.c | 3 +-
mm/migrate.c | 3 +-
mm/mmu_notifier.c | 15 ++++++++++
mm/rmap.c | 2 +-
10 files changed, 95 insertions(+), 18 deletions(-)

--
1.9.1



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