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Date:   Wed, 30 Aug 2017 07:19:30 +1000
From:   Benjamin Herrenschmidt <>
To:     Peter Zijlstra <>
Cc:     "Kirill A. Shutemov" <>,
        Laurent Dufour <>,,,,,,, Matthew Wilcox <>,,,
        Thomas Gleixner <>,
        Ingo Molnar <>,,
        Will Deacon <>,,,,,,,
        Tim Chen <>,,
Subject: Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure

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" :-)


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