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    SubjectRe: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable
    On Fri, Aug 27, 2021 at 12:33:00PM -0700, Linus Torvalds wrote:
    > On Fri, Aug 27, 2021 at 12:23 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
    > >
    > > Could you show the cases where "partial copy, so it's OK" behaviour would
    > > break anything?
    >
    > Absolutely.
    >
    > For example, i t would cause an infinite loop in
    > restore_fpregs_from_user() if the "buf" argument is a situation where
    > the first page is fine, but the next page is not.
    >
    > Why? Because __restore_fpregs_from_user() would take a fault, but then
    > fault_in_pages_readable() (renamed) would succeed, so you'd just do
    > that "retry" forever and ever.
    >
    > Probably there are a number of other places too. That was literally
    > the *first* place I looked at.

    OK...

    Let me dig out the notes from the last time I looked through that area
    and grep around a bit. Should be about an hour or two.

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