powerpc: Add support for context switching the TAR register
This patch adds support for enabling and context switching the Target
Address Register in Power8. The TAR is a new special purpose register
that can be used for computed branches with the bctar[l] (branch
conditional to TAR) instruction in the same manner as the count and link
registers.
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 44c733f..9ae8451 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -448,6 +448,19 @@
std r23,_CCR(r1)
std r1,KSP(r3) /* Set old stack pointer */
+#ifdef CONFIG_PPC_BOOK3S_64
+BEGIN_FTR_SECTION
+ /*
+ * Back up the TAR across context switches. Note that the TAR is not
+ * available for use in the kernel. (To provide this, the TAR should
+ * be backed up/restored on exception entry/exit instead, and be in
+ * pt_regs. FIXME, this should be in pt_regs anyway (for debug).)
+ */
+ mfspr r0,SPRN_TAR
+ std r0,THREAD_TAR(r3)
+END_FTR_SECTION_IFSET(CPU_FTR_BCTAR)
+#endif
+
#ifdef CONFIG_SMP
/* We need a sync somewhere here to make sure that if the
* previous task gets rescheduled on another CPU, it sees all
@@ -530,6 +543,13 @@
mr r1,r8 /* start using new stack pointer */
std r7,PACAKSAVE(r13)
+#ifdef CONFIG_PPC_BOOK3S_64
+BEGIN_FTR_SECTION
+ ld r0,THREAD_TAR(r4)
+ mtspr SPRN_TAR,r0
+END_FTR_SECTION_IFSET(CPU_FTR_BCTAR)
+#endif
+
#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
ld r0,THREAD_VRSAVE(r4)