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    SubjectRe: xtensa question, was Re: [PATCH V1 00/10] Remove duplicated kmap code
    On Fri, May 1, 2020 at 2:19 AM Christoph Hellwig <hch@infradead.org> wrote:
    >
    > On Fri, May 01, 2020 at 02:02:19AM -0700, Max Filippov wrote:
    > > Hi Christoph,
    > >
    > > On Fri, May 1, 2020 at 1:46 AM Christoph Hellwig <hch@infradead.org> wrote:
    > > > any idea why xtensa uses PAGE_KERNEL_EXEC instead of PAGE_KERNEL
    > > > for kmap_prot? Mapping all mapped highmem as executable seems rather
    > > > dangerous.
    > >
    > > I sure do: to allow instruction cache flushing when writing to high user
    > > pages temporarily mapped with kmap. Instruction cache management
    > > opcodes that operate on virtual addresses would raise an exception if
    > > the address is not executable.
    >
    > Seems like this should use kmap_atomic_prot with PAGE_KERNEL_EXEC just
    > for that case. Which of course didn't exist on xtensa so far, but with
    > this series will.

    Yeah, except it's the __access_remote_vm that does the kmap and then
    calls copy_to_user_page...

    --
    Thanks.
    -- Max

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