Messages in this thread | | | From | Joerg Roedel <> | Subject | [PATCH 0/3] mmu_notifier: Allow to manage CPU external TLBs | Date | Thu, 24 Jul 2014 16:35:38 +0200 |
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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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