openrisc: Move FPU state out of pt_regs

My original, naive, FPU support patch had the FPCSR register stored
during both the *mode switch* and *context switch*.  This is wasteful.

Also, the original patches did not save the FPU state when handling
signals during the system call fast path.

We fix this by moving the FPCSR state to thread_struct in task_struct.
We also introduce new helper functions save_fpu and restore_fpu which
can be used to sync the FPU with thread_struct.  These functions are now
called when needed:

 - Setting up and restoring sigcontext when handling signals
 - Before and after __switch_to during context switches
 - When handling FPU exceptions
 - When reading and writing FPU register sets

In the future we can further optimize this by doing lazy FPU save and
restore.  For example, FPU sync is not needed when switching to and from
kernel threads (x86 does this).  FPU save and restore does not need to
be done two times if we have both rescheduling and signal work to do.
However, since OpenRISC FPU state is a single register, I leave these
optimizations for future consideration.

Signed-off-by: Stafford Horne <[email protected]>

1 files changed, 34 insertions, 2 deletions

diff --git a/arch/openrisc/kernel/signal.c b/arch/openrisc/kernel/signal.c
index e2f21a5d8ad9..c7ab42e2cb7a 100644
--- a/arch/openrisc/kernel/signal.c
+++ b/arch/openrisc/kernel/signal.c
@@ -23,6 +23,7 @@
 #include <linux/stddef.h>
 #include <linux/resume_user_mode.h>
 
+#include <asm/fpu.h>
 #include <asm/processor.h>
 #include <asm/syscall.h>
 #include <asm/ucontext.h>
@@ -39,6 +40,37 @@ asmlinkage long _sys_rt_sigreturn(struct pt_regs *regs);
 asmlinkage int do_work_pending(struct pt_regs *regs, unsigned int thread_flags,
 			       int syscall);
 
+#ifdef CONFIG_FPU
+static long restore_fp_state(struct sigcontext __user *sc)
+{
+	long err;
+
+	err = __copy_from_user(&current->thread.fpcsr, &sc->fpcsr, sizeof(unsigned long));
+	if (unlikely(err))
+		return err;
+
+	/* Restore the FPU state */
+	restore_fpu(current);
+
+	return 0;
+}
+
+static long save_fp_state(struct sigcontext __user *sc)
+{
+	long err;
+
+	/* Sync the user FPU state so we can copy to sigcontext */
+	save_fpu(current);
+
+	err = __copy_to_user(&sc->fpcsr, &current->thread.fpcsr, sizeof(unsigned long));
+
+	return err;
+}
+#else
+#define save_fp_state(sc) (0)
+#define restore_fp_state(sc) (0)
+#endif
+
 static int restore_sigcontext(struct pt_regs *regs,
 			      struct sigcontext __user *sc)
 {
@@ -55,7 +87,7 @@ static int restore_sigcontext(struct pt_regs *regs,
 	err |= __copy_from_user(regs, sc->regs.gpr, 32 * sizeof(unsigned long));
 	err |= __copy_from_user(&regs->pc, &sc->regs.pc, sizeof(unsigned long));
 	err |= __copy_from_user(&regs->sr, &sc->regs.sr, sizeof(unsigned long));
-	err |= __copy_from_user(&regs->fpcsr, &sc->fpcsr, sizeof(unsigned long));
+	err |= restore_fp_state(sc);
 
 	/* make sure the SM-bit is cleared so user-mode cannot fool us */
 	regs->sr &= ~SPR_SR_SM;
@@ -118,7 +150,7 @@ static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 	err |= __copy_to_user(sc->regs.gpr, regs, 32 * sizeof(unsigned long));
 	err |= __copy_to_user(&sc->regs.pc, &regs->pc, sizeof(unsigned long));
 	err |= __copy_to_user(&sc->regs.sr, &regs->sr, sizeof(unsigned long));
-	err |= __copy_to_user(&sc->fpcsr, &regs->fpcsr, sizeof(unsigned long));
+	err |= save_fp_state(sc);
 
 	return err;
 }