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    SubjectRe: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect
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    > On Jan 12, 2021, at 1:43 PM, Will Deacon <will@kernel.org> wrote:
    >
    > On Tue, Jan 12, 2021 at 12:38:34PM -0800, Nadav Amit wrote:
    >>> On Jan 12, 2021, at 11:56 AM, Yu Zhao <yuzhao@google.com> wrote:
    >>> On Tue, Jan 12, 2021 at 11:15:43AM -0800, Nadav Amit wrote:
    >>>> I will send an RFC soon for per-table deferred TLB flushes tracking.
    >>>> The basic idea is to save a generation in the page-struct that tracks
    >>>> when deferred PTE change took place, and track whenever a TLB flush
    >>>> completed. In addition, other users - such as mprotect - would use
    >>>> the tlb_gather interface.
    >>>>
    >>>> Unfortunately, due to limited space in page-struct this would only
    >>>> be possible for 64-bit (and my implementation is only for x86-64).
    >>>
    >>> I don't want to discourage you but I don't think this would end up
    >>> well. PPC doesn't necessarily follow one-page-struct-per-table rule,
    >>> and I've run into problems with this before while trying to do
    >>> something similar.
    >>
    >> Discourage, discourage. Better now than later.
    >>
    >> It will be relatively easy to extend the scheme to be per-VMA instead of
    >> per-table for architectures that prefer it this way. It does require
    >> TLB-generation tracking though, which Andy only implemented for x86, so I
    >> will focus on x86-64 right now.
    >
    > Can you remind me of what we're missing on arm64 in this area, please? I'm
    > happy to help get this up and running once you have something I can build
    > on.

    Let me first finish making something that we can use as a basis for a
    discussion. I do not waste your time before I have something ready.

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