powerpc: Provide for giveup_fpu/altivec to save state in alternate location

This provides a facility which is intended for use by KVM, where the
contents of the FP/VSX and VMX (Altivec) registers can be saved away
to somewhere other than the thread_struct when kernel code wants to
use floating point or VMX instructions.  This is done by providing a
pointer in the thread_struct to indicate where the state should be
saved to.  The giveup_fpu() and giveup_altivec() functions test these
pointers and save state to the indicated location if they are non-NULL.
Note that the MSR_FP/VEC bits in task->thread.regs->msr are still used
to indicate whether the CPU register state is live, even when an
alternate save location is being used.

This also provides load_fp_state() and load_vr_state() functions, which
load up FP/VSX and VMX state from memory into the CPU registers, and
corresponding store_fp_state() and store_vr_state() functions, which
store FP/VSX and VMX state into memory from the CPU registers.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 7a281416affb..8649a3d629e1 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1008,6 +1008,11 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
         p->thread.ptrace_bps[0] = NULL;
 #endif
 
+        p->thread.fp_save_area = NULL;
+#ifdef CONFIG_ALTIVEC
+        p->thread.vr_save_area = NULL;
+#endif
+
 #ifdef CONFIG_PPC_STD_MMU_64
         if (mmu_has_feature(MMU_FTR_SLB)) {
                 unsigned long sp_vsid;
@@ -1114,9 +1119,11 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
         current->thread.used_vsr = 0;
 #endif
         memset(&current->thread.fp_state, 0, sizeof(current->thread.fp_state));
+        current->thread.fp_save_area = NULL;
 #ifdef CONFIG_ALTIVEC
         memset(&current->thread.vr_state, 0, sizeof(current->thread.vr_state));
         current->thread.vr_state.vscr.u[3] = 0x00010000; /* Java mode disabled */
+        current->thread.vr_save_area = NULL;
         current->thread.vrsave = 0;
         current->thread.used_vr = 0;
 #endif /* CONFIG_ALTIVEC */