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H A D | process.c | diff e901378578c62202594cba0f6c076f3df365ec91 Wed Oct 24 15:57:22 CEST 2018 Felipe Rechia <felipe.rechia@datacom.com.br> powerpc/process: Fix flush_all_to_thread for SPE
Fix a bug introduced by the creation of flush_all_to_thread() for processors that have SPE (Signal Processing Engine) and use it to compute floating-point operations.
>From userspace perspective, the problem was seen in attempts of computing floating-point operations which should generate exceptions. For example:
fork(); float x = 0.0 / 0.0; isnan(x); // forked process returns False (should be True)
The operation above also should always cause the SPEFSCR FINV bit to be set. However, the SPE floating-point exceptions were turned off after a fork().
Kernel versions prior to the bug used flush_spe_to_thread(), which first saves SPEFSCR register values in tsk->thread and then calls giveup_spe(tsk).
After commit 579e633e764e, the save_all() function was called first to giveup_spe(), and then the SPEFSCR register values were saved in tsk->thread. This would save the SPEFSCR register values after disabling SPE for that thread, causing the bug described above.
Fixes 579e633e764e ("powerpc: create flush_all_to_thread()") Signed-off-by: Felipe Rechia <felipe.rechia@datacom.com.br> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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