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Date:   Fri, 31 Aug 2018 10:52:02 -0700
From:   Dave Hansen <>
To:     Andy Lutomirski <>
Cc:     Jann Horn <>, Yu-cheng Yu <>,
        the arch/x86 maintainers <>,
        "H . Peter Anvin" <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        kernel list <>,, Linux-MM <>,
        linux-arch <>,
        Linux API <>,
        Arnd Bergmann <>,
        Balbir Singh <>,
        Cyrill Gorcunov <>,
        Florian Weimer <>,
        "H. J. Lu" <>, Jonathan Corbet <>,
        Kees Cook <>,
        Mike Kravetz <>,
        Nadav Amit <>,
        Oleg Nesterov <>, Pavel Machek <>,
        Peter Zijlstra <>,
        "Ravi V. Shankar" <>,
        "Shanbhogue, Vedvyas" <>
Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and
 pmdp_set_wrprotect for _PAGE_DIRTY_SW

On 08/31/2018 10:46 AM, Andy Lutomirski wrote:
> On Thu, Aug 30, 2018 at 11:55 AM, Dave Hansen
>> That little hunk will definitely need to get updated with something like:
>>         On processors enumerating support for CET, the processor will on
>>         set the dirty flag on paging structure entries in which the W
>>         flag is 1.
> Can we get something much stronger, perhaps?  Like this:
> On processors enumerating support for CET, the processor will write to
> the accessed and/or dirty flags atomically, as if using the LOCK
> CMPXCHG instruction.  The memory access, any cached entries in any
> paging-structure caches, and the values in the paging-structure entry
> before and after writing the A and/or D bits will all be consistent.

There's some talk of this already in: Automatic Locking:

> When updating page-directory and page-table entries — When updating 
> page-directory and page-table entries, the processor uses locked 
> cycles to set the accessed and dirty flag in the page-directory and
> page-table entries.
As for the A/D consistency, I'll see if I can share that before it hits
the SDM for real and see if it's sufficient for everybody.

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