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Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure

From Benjamin Herrenschmidt <benh@kernel.crashing.org>
Newsgroups linux.kernel
Subject Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure
Date 2017-08-30 00:00 +0200
Message-ID <ujWIb-84B-47@gated-at.bofh.it> (permalink)
References (2 earlier) <uiTsZ-8fp-1@gated-at.bofh.it> <ujoGu-3Tj-25@gated-at.bofh.it> <ujzLA-2eP-17@gated-at.bofh.it> <ujKdY-i4-5@gated-at.bofh.it> <ujMSu-1Zf-25@gated-at.bofh.it>
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On Tue, 2017-08-29 at 13:27 +0200, Peter Zijlstra wrote:
> mpe helped me out and explained that is the PWC hint to TBLIE.
> 
> So, you set need_flush_all when you unhook pud/pmd/pte which you then
> use to set PWC. So free_pgtables() will do the PWC when it unhooks
> higher level pages.
> 
> But you're right that there's some issues, free_pgtables() itself
> doesn't seem to use mm->page_table_lock,pmd->lock _AT_ALL_ to unhook the
> pages.
> 
> If it were to do that, things should work fine since those locks would
> then serialize against the speculative faults, we would never install a
> page if the VMA would be under tear-down and it would thus not be
> visible to your caches either.

That's one case. I don't remember of *all* the cases to be honest, but
I do remember several times over the past few years thinking "ah we are
fine because the mm sem taken for writing protects us from any
concurrent tree structure change" :-)

Cheers,
Ben.

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Thread

Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-08-27 02:20 +0200
  Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-28 11:40 +0200
    Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-08-28 23:30 +0200
      Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Andi Kleen <ak@linux.intel.com> - 2017-08-29 00:40 +0200
        Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-29 10:20 +0200
      Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-29 10:40 +0200
        Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-29 13:30 +0200
          Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-08-30 00:00 +0200
            Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-30 08:20 +0200
  Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-08-29 10:00 +0200
    Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-29 14:10 +0200
      Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-08-29 15:20 +0200
        Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-29 15:50 +0200
          Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-08-30 07:10 +0200
            Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-30 08:00 +0200
              Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-08-30 11:40 +0200
                Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-08-31 09:00 +0200
                Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Peter Zijlstra <peterz@infradead.org> - 2017-08-31 09:40 +0200
            Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-08-30 12:00 +0200
      Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-08-30 05:50 +0200
  Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-08-30 07:30 +0200
  Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-08-30 11:00 +0200

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