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

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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>
This commit is contained in:
Cyril Bur 2016-02-29 17:53:49 +11:00 • committed by Michael Ellerman
parent de2a20aa72
commit 8792468da5
3 changed files with 17 additions and 19 deletions
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12
arch/powerpc/kernel/process.c
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@ -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);