powerpc: Disable VSX or current process in giveup_fpu/altivec

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When we call giveup_fpu, we need to need to turn off VSX for the
current process.  If we don't, on return to userspace it may execute a
VSX instruction before the next FP instruction, and not have its
register state refreshed correctly from the thread_struct.  Ditto for
altivec.

This caused a bug where an unaligned lfs or stfs results in
fix_alignment calling giveup_fpu so it can use the FPRs (in order to
do a single <-> double conversion), and then returning to userspace
with FP off but VSX on.  Then if a VSX instruction is executed, before
another FP instruction, it will proceed without another exception and
hence have the incorrect register state for VSX registers 0-31.

   lfs unaligned   <- alignment exception turns FP off but leaves VSX on

   VSX instruction <- no exception since VSX on, hence we get the
                      wrong VSX register values for VSX registers 0-31,
                      which overlap the FPRs.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

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This commit is contained in:

Michael Neuling 2009-04-01 18:02:42 +00:00 • committed by Paul Mackerras

parent 4c6cf42843

commit 7e875e9dc8

2 changed files with 13 additions and 0 deletions

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5

arch/powerpc/kernel/fpu.S

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8

arch/powerpc/kernel/misc_64.S

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