powerpc: Add the ability to save FPU without giving it up

This patch adds the ability to be able to save the FPU registers to the
thread struct without giving up (disabling the facility) next time the
process returns to userspace.

This patch optimises the thread copy path (as a result of a fork() or
clone()) so that the parent thread can return to userspace with hot
registers avoiding a possibly pointless reload of FPU register state.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 11 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 29da07fb3b4a..a7e5061187e8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -133,6 +133,16 @@ void __msr_check_and_clear(unsigned long bits)
 EXPORT_SYMBOL(__msr_check_and_clear);
 
 #ifdef CONFIG_PPC_FPU
+void __giveup_fpu(struct task_struct *tsk)
+{
+        save_fpu(tsk);
+        tsk->thread.regs->msr &= ~MSR_FP;
+#ifdef CONFIG_VSX
+        if (cpu_has_feature(CPU_FTR_VSX))
+                tsk->thread.regs->msr &= ~MSR_VSX;
+#endif
+}
+
 void giveup_fpu(struct task_struct *tsk)
 {
         check_if_tm_restore_required(tsk);
@@ -459,7 +469,7 @@ void save_all(struct task_struct *tsk)
         msr_check_and_set(msr_all_available);
 
         if (usermsr & MSR_FP)
-                __giveup_fpu(tsk);
+                save_fpu(tsk);
 
         if (usermsr & MSR_VEC)
                 __giveup_altivec(tsk);