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    SubjectRe: Interrupt handling
    On Thu, 16 Oct 2003, Richard B. Johnson wrote:

    > The memory-map idea has security problems, though.
    > If the area ever gets unmapped (the user exits), a
    > fatal error could occur in kernel mode within the
    > ISR. In general, it's always best to allocate an
    > interrupt-safe buffer within the driver (module),
    > that is guaranteed to persist as long as the driver
    > is installed. This ultimately means that a copy
    > operation is necessary.
    > Memory-to-memory copy is real fast now days. The
    > copy_to_user() is just memcpy() with a trap mechanism
    > that can save the kernel from a user-induced seg-fault.
    > The actual trap is hardware-induced in ix86 machines
    > and therefore adds no overhead to the normal copy operation.

    Is there any reason why we couldn't via kernel routine let user space
    access read-only certain pages of kernel memory? I.e. having the
    userspace function call the driver to map into it's (user) address space a
    read-only mapping of the drivers (kernel) private r/w area?
    If I'm not mistaken this is doable on x86 hardware isn't it?


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