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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?

Cheers,
MaZe.

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