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>

6 files changed, 38 insertions, 1 deletions

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index 06f7fb93c547..5f1938fcce40 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -414,7 +414,7 @@ extern const char *powerpc_base_platform;
             CPU_FTR_DSCR | CPU_FTR_SAO  | \
             CPU_FTR_STCX_CHECKS_ADDRESS | CPU_FTR_POPCNTB | CPU_FTR_POPCNTD | \
             CPU_FTR_ICSWX | CPU_FTR_CFAR | CPU_FTR_HVMODE | CPU_FTR_VMX_COPY | \
-            CPU_FTR_DBELL | CPU_FTR_HAS_PPR | CPU_FTR_DAWR)
+            CPU_FTR_DBELL | CPU_FTR_HAS_PPR | CPU_FTR_DAWR | CPU_FTR_BCTAR)
 #define CPU_FTRS_CELL   (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
             CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
             CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 7938658c168d..42ac53cebacd 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -257,6 +257,9 @@ struct thread_struct {
         int             dscr_inherit;
         unsigned long   ppr;    /* used to save/restore SMT priority */
 #endif
+#ifdef CONFIG_PPC_BOOK3S_64
+        unsigned long   tar;
+#endif
 };
 
 #define ARCH_MIN_TASKALIGN 16
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 1f59fbb7b054..e09ac51961d7 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -237,6 +237,9 @@
 #define SPRN_HRMOR      0x139   /* Real mode offset register */
 #define SPRN_HSRR0      0x13A   /* Hypervisor Save/Restore 0 */
 #define SPRN_HSRR1      0x13B   /* Hypervisor Save/Restore 1 */
+#define SPRN_FSCR       0x099   /* Facility Status & Control Register */
+#define FSCR_TAR        (1<<8)  /* Enable Target Adress Register */
+#define SPRN_TAR        0x32f   /* Target Address Register */
 #define SPRN_LPCR       0x13E   /* LPAR Control Register */
 #define   LPCR_VPM0     (1ul << (63-0))
 #define   LPCR_VPM1     (1ul << (63-1))
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index e39ca556e87f..beddba432518 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -122,6 +122,10 @@ int main(void)
         DEFINE(THREAD_KVM_VCPU, offsetof(struct thread_struct, kvm_vcpu));
 #endif
 
+#ifdef CONFIG_PPC_BOOK3S_64
+        DEFINE(THREAD_TAR, offsetof(struct thread_struct, tar));
+#endif
+
         DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
         DEFINE(TI_LOCAL_FLAGS, offsetof(struct thread_info, local_flags));
         DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
diff --git a/arch/powerpc/kernel/cpu_setup_power.S b/arch/powerpc/kernel/cpu_setup_power.S
index 57cf14065aec..d29facbf9a28 100644
--- a/arch/powerpc/kernel/cpu_setup_power.S
+++ b/arch/powerpc/kernel/cpu_setup_power.S
@@ -56,6 +56,7 @@ _GLOBAL(__setup_cpu_power8)
         mfspr   r3,SPRN_LPCR
         oris    r3, r3, LPCR_AIL_3@h
         bl      __init_LPCR
+        bl      __init_FSCR
         bl      __init_TLB
         mtlr    r11
         blr
@@ -112,6 +113,12 @@ __init_LPCR:
         isync
         blr
 
+__init_FSCR:
+        mfspr   r3,SPRN_FSCR
+        ori     r3,r3,FSCR_TAR
+        mtspr   SPRN_FSCR,r3
+        blr
+
 __init_TLB:
         /* Clear the TLB */
         li      r6,128
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 44c733f4f829..9ae8451bbc83 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -448,6 +448,19 @@ END_FTR_SECTION_IFSET(CPU_FTR_DSCR)
         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 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
         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)