On Wed, Oct 06, 2004 at 10:19:20AM +0900, Atsushi Nemoto wrote:
> I found a potential problem in math emulation. The math-emu uses
> put_user/get_user to fetch the instruction or to emulate load/store
> fp-regs. The put_user/get_user can sleep then we can lose fpu
> ownership on it. It it happened, subsequent restore_fp will cause CpU
> exception which not allowed in kernel.
>
> Here is a quick fix. Can be applied bath 2.4 and 2.6. Could you apply?
>
I don't feel good about this patch. If emulator loses FPU ownership it should
get it back, not the caller of emulator.
Jun
> --- linux-mips/arch/mips/kernel/traps.c Sat Aug 14 19:55:20 2004
> +++ linux/arch/mips/kernel/traps.c Wed Oct 6 09:50:26 2004
> @@ -509,6 +509,10 @@
> /* Run the emulator */
> sig = fpu_emulator_cop1Handler (0, regs,
> ¤t->thread.fpu.soft);
> + if (!is_fpu_owner()) {
> + /* We might lose fpu in fpu_emulator. */
> + own_fpu();
> + }
>
> /*
> * We can't allow the emulated instruction to leave any of
>
>
> Also, there is another problem in the math-emu. While math-emu is not
> reentrant, it will not work properly if a process lose ownership in
> the math-emu and another process uses the math-emu. One possible fix
> is to save/restore ieee754_csr on get_user/put_user. I will post a
> patch later.
>
> ---
> Atsushi Nemoto
