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Date:   Fri, 6 Mar 2020 19:34:18 -0500
From:   Qian Cai <>
To:     Anshuman Khandual <>
Cc:, Andrew Morton <>,
        Mike Rapoport <>,
        Vineet Gupta <>,
        Catalin Marinas <>,
        Will Deacon <>,
        Benjamin Herrenschmidt <>,
        Paul Mackerras <>,
        Michael Ellerman <>,
        Heiko Carstens <>,
        Vasily Gorbik <>,
        Christian Borntraeger <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        "H. Peter Anvin" <>,
        "Kirill A . Shutemov" <>,
        Paul Walmsley <>,
        Palmer Dabbelt <>,,,,,,,,,
        Christophe Leroy <>
Subject: Re: [PATCH V15] mm/debug: Add tests validating architecture page table helpers

> On Mar 6, 2020, at 7:03 PM, Anshuman Khandual <> wrote:
> Hmm, set_pte_at() function is not preferred here for these tests. The idea
> is to avoid or atleast minimize TLB/cache flushes triggered from these sort
> of 'static' tests. set_pte_at() is platform provided and could/might trigger
> these flushes or some other platform specific synchronization stuff. Just

Why is that important for this debugging option?

> wondering is there specific reason with respect to the soft lock up problem
> making it necessary to use set_pte_at() rather than a simple WRITE_ONCE() ?

Looks at the s390 version of set_pte_at(), it has this comment,

 * Certain architectures need to do special things when PTEs
 * within a page table are directly modified.  Thus, the following
 * hook is made available.

I can only guess that powerpc  could be the same here.

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