powerpc: Disable VSX or current process in giveup_fpu/altivec
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>
diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
index 3053fe5..b9530b2 100644
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -495,7 +495,15 @@
stvx vr0,r4,r3
beq 1f
ld r4,_MSR-STACK_FRAME_OVERHEAD(r5)
+#ifdef CONFIG_VSX
+BEGIN_FTR_SECTION
+ lis r3,(MSR_VEC|MSR_VSX)@h
+FTR_SECTION_ELSE
lis r3,MSR_VEC@h
+ALT_FTR_SECTION_END_IFSET(CPU_FTR_VSX)
+#else
+ lis r3,MSR_VEC@h
+#endif
andc r4,r4,r3 /* disable FP for previous task */
std r4,_MSR-STACK_FRAME_OVERHEAD(r5)
1: