powerpc: Make it possible to move the interrupt handlers away from the kernel

This changes the way that the exception prologs transfer control to
the handlers in 64-bit kernels with the aim of making it possible to
have the prologs separate from the main body of the kernel.  Now,
instead of computing the address of the handler by taking the top
32 bits of the paca address (to get the 0xc0000000........ part) and
ORing in something in the bottom 16 bits, we get the base address of
the kernel by doing a load from the paca and add an offset.

This also replaces an mfmsr and an ori to compute the MSR value for
the handler with a load from the paca.  That makes it unnecessary to
have a separate version of EXCEPTION_PROLOG_PSERIES that forces 64-bit
mode.

We can no longer use a direct branches in the exception prolog code,
which means that the SLB miss handlers can't branch directly to
.slb_miss_realmode any more.  Instead we have to compute the address
and do an indirect branch.  This is conditional on CONFIG_RELOCATABLE;
for non-relocatable kernels we use a direct branch as before.  (A later
change will allow CONFIG_RELOCATABLE to be set on 64-bit powerpc.)

Since the secondary CPUs on pSeries start execution in the first 0x100
bytes of real memory and then have to get to wherever the kernel is,
we can't use a direct branch to get there.  Instead this changes
__secondary_hold_spinloop from a flag to a function pointer.  When it
is set to a non-NULL value, the secondary CPUs jump to the function
pointed to by that value.

Finally this eliminates one code difference between 32-bit and 64-bit
by making __secondary_hold be the text address of the secondary CPU
spinloop rather than a function descriptor for it.

Signed-off-by: Paul Mackerras <paulus@samba.org>

5 files changed, 65 insertions, 27 deletions

diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 92768d3006f7..e9c4044012bd 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -122,6 +122,8 @@ int main(void)
         DEFINE(PACASTABRR, offsetof(struct paca_struct, stab_rr));
         DEFINE(PACAR1, offsetof(struct paca_struct, saved_r1));
         DEFINE(PACATOC, offsetof(struct paca_struct, kernel_toc));
+        DEFINE(PACAKBASE, offsetof(struct paca_struct, kernelbase));
+        DEFINE(PACAKMSR, offsetof(struct paca_struct, kernel_msr));
         DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));
         DEFINE(PACAHARDIRQEN, offsetof(struct paca_struct, hard_enabled));
         DEFINE(PACASLBCACHE, offsetof(struct paca_struct, slb_cache));
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 27935d1ab6a1..97bb6e6f67b1 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -82,7 +82,11 @@ END_FTR_SECTION(0, 1)
         /* Catch branch to 0 in real mode */
         trap
 
-        /* Secondary processors spin on this value until it goes to 1. */
+        /* Secondary processors spin on this value until it becomes nonzero.
+         * When it does it contains the real address of the descriptor
+         * of the function that the cpu should jump to to continue
+         * initialization.
+         */
         .globl  __secondary_hold_spinloop
 __secondary_hold_spinloop:
         .llong  0x0
@@ -109,8 +113,11 @@ __secondary_hold_acknowledge:
  * before the bulk of the kernel has been relocated.  This code
  * is relocated to physical address 0x60 before prom_init is run.
  * All of it must fit below the first exception vector at 0x100.
+ * Use .globl here not _GLOBAL because we want __secondary_hold
+ * to be the actual text address, not a descriptor.
  */
-_GLOBAL(__secondary_hold)
+        .globl  __secondary_hold
+__secondary_hold:
         mfmsr   r24
         ori     r24,r24,MSR_RI
         mtmsrd  r24                     /* RI on */
@@ -126,11 +133,11 @@ _GLOBAL(__secondary_hold)
 
         /* All secondary cpus wait here until told to start. */
 100:    ld      r4,__secondary_hold_spinloop@l(0)
-        cmpdi   0,r4,1
-        bne     100b
+        cmpdi   0,r4,0
+        beq     100b
 
 #if defined(CONFIG_SMP) || defined(CONFIG_KEXEC)
-        LOAD_REG_IMMEDIATE(r4, .generic_secondary_smp_init)
+        ld      r4,0(r4)                /* deref function descriptor */
         mtctr   r4
         mr      r3,r24
         bctr
@@ -147,6 +154,10 @@ exception_marker:
 /*
  * This is the start of the interrupt handlers for pSeries
  * This code runs with relocation off.
+ * Code from here to __end_interrupts gets copied down to real
+ * address 0x100 when we are running a relocatable kernel.
+ * Therefore any relative branches in this section must only
+ * branch to labels in this section.
  */
         . = 0x100
         .globl __start_interrupts
@@ -200,7 +211,20 @@ data_access_slb_pSeries:
         mfspr   r10,SPRN_SPRG1
         std     r10,PACA_EXSLB+EX_R13(r13)
         mfspr   r12,SPRN_SRR1           /* and SRR1 */
-        b       .slb_miss_realmode      /* Rel. branch works in real mode */
+#ifndef CONFIG_RELOCATABLE
+        b       .slb_miss_realmode
+#else
+        /*
+         * We can't just use a direct branch to .slb_miss_realmode
+         * because the distance from here to there depends on where
+         * the kernel ends up being put.
+         */
+        mfctr   r11
+        ld      r10,PACAKBASE(r13)
+        LOAD_HANDLER(r10, .slb_miss_realmode)
+        mtctr   r10
+        bctr
+#endif
 
         STD_EXCEPTION_PSERIES(0x400, instruction_access)
 
@@ -225,7 +249,15 @@ instruction_access_slb_pSeries:
         mfspr   r10,SPRN_SPRG1
         std     r10,PACA_EXSLB+EX_R13(r13)
         mfspr   r12,SPRN_SRR1           /* and SRR1 */
-        b       .slb_miss_realmode      /* Rel. branch works in real mode */
+#ifndef CONFIG_RELOCATABLE
+        b       .slb_miss_realmode
+#else
+        mfctr   r11
+        ld      r10,PACAKBASE(r13)
+        LOAD_HANDLER(r10, .slb_miss_realmode)
+        mtctr   r10
+        bctr
+#endif
 
         MASKABLE_EXCEPTION_PSERIES(0x500, hardware_interrupt)
         STD_EXCEPTION_PSERIES(0x600, alignment)
@@ -244,14 +276,12 @@ BEGIN_FTR_SECTION
         beq-    1f
 END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE)
         mr      r9,r13
-        mfmsr   r10
         mfspr   r13,SPRN_SPRG3
         mfspr   r11,SPRN_SRR0
-        clrrdi  r12,r13,32
-        oris    r12,r12,system_call_common@h
-        ori     r12,r12,system_call_common@l
+        ld      r12,PACAKBASE(r13)
+        ld      r10,PACAKMSR(r13)
+        LOAD_HANDLER(r12, system_call_entry)
         mtspr   SPRN_SRR0,r12
-        ori     r10,r10,MSR_IR|MSR_DR|MSR_RI
         mfspr   r12,SPRN_SRR1
         mtspr   SPRN_SRR1,r10
         rfid
@@ -379,7 +409,10 @@ __end_interrupts:
 
 /*
  * Code from here down to __end_handlers is invoked from the
- * exception prologs above.
+ * exception prologs above.  Because the prologs assemble the
+ * addresses of these handlers using the LOAD_HANDLER macro,
+ * which uses an addi instruction, these handlers must be in
+ * the first 32k of the kernel image.
  */
 
 /*** Common interrupt handlers ***/
@@ -419,6 +452,10 @@ machine_check_common:
         STD_EXCEPTION_COMMON(0x1800, cbe_thermal, .cbe_thermal_exception)
 #endif /* CONFIG_CBE_RAS */
 
+        .align  7
+system_call_entry:
+        b       system_call_common
+
 /*
  * Here we have detected that the kernel stack pointer is bad.
  * R9 contains the saved CR, r13 points to the paca,
@@ -562,6 +599,9 @@ unrecov_user_slb:
  */
 _GLOBAL(slb_miss_realmode)
         mflr    r10
+#ifdef CONFIG_RELOCATABLE
+        mtctr   r11
+#endif
 
         stw     r9,PACA_EXSLB+EX_CCR(r13)       /* save CR in exc. frame */
         std     r10,PACA_EXSLB+EX_LR(r13)       /* save LR */
@@ -612,11 +652,10 @@ BEGIN_FW_FTR_SECTION
 END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
 #endif /* CONFIG_PPC_ISERIES */
         mfspr   r11,SPRN_SRR0
-        clrrdi  r10,r13,32
+        ld      r10,PACAKBASE(r13)
         LOAD_HANDLER(r10,unrecov_slb)
         mtspr   SPRN_SRR0,r10
-        mfmsr   r10
-        ori     r10,r10,MSR_IR|MSR_DR|MSR_RI
+        ld      r10,PACAKMSR(r13)
         mtspr   SPRN_SRR1,r10
         rfid
         b       .
diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index c9bf17eec31b..623e8c3c57f9 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -79,6 +79,8 @@ void __init initialise_pacas(void)
                 new_paca->lock_token = 0x8000;
                 new_paca->paca_index = cpu;
                 new_paca->kernel_toc = kernel_toc;
+                new_paca->kernelbase = KERNELBASE;
+                new_paca->kernel_msr = MSR_KERNEL;
                 new_paca->hw_cpu_id = 0xffff;
                 new_paca->slb_shadow_ptr = &slb_shadow[cpu];
                 new_paca->__current = &init_task;
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index b72849ac7db3..1f8988585054 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -1321,7 +1321,7 @@ static void __init prom_initialize_tce_table(void)
  *
  * -- Cort
  */
-extern void __secondary_hold(void);
+extern char __secondary_hold;
 extern unsigned long __secondary_hold_spinloop;
 extern unsigned long __secondary_hold_acknowledge;
 
@@ -1342,13 +1342,7 @@ static void __init prom_hold_cpus(void)
                 = (void *) LOW_ADDR(__secondary_hold_spinloop);
         unsigned long *acknowledge
                 = (void *) LOW_ADDR(__secondary_hold_acknowledge);
-#ifdef CONFIG_PPC64
-        /* __secondary_hold is actually a descriptor, not the text address */
-        unsigned long secondary_hold
-                = __pa(*PTRRELOC((unsigned long *)__secondary_hold));
-#else
         unsigned long secondary_hold = LOW_ADDR(__secondary_hold);
-#endif
 
         prom_debug("prom_hold_cpus: start...\n");
         prom_debug("    1) spinloop       = 0x%x\n", (unsigned long)spinloop);
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 8b25f51f03bf..843c0af210d0 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -255,9 +255,11 @@ void early_setup_secondary(void)
 #endif /* CONFIG_SMP */
 
 #if defined(CONFIG_SMP) || defined(CONFIG_KEXEC)
+extern unsigned long __secondary_hold_spinloop;
+extern void generic_secondary_smp_init(void);
+
 void smp_release_cpus(void)
 {
-        extern unsigned long __secondary_hold_spinloop;
         unsigned long *ptr;
 
         DBG(" -> smp_release_cpus()\n");
@@ -266,12 +268,11 @@ void smp_release_cpus(void)
          * all now so they can start to spin on their individual paca
          * spinloops. For non SMP kernels, the secondary cpus never get out
          * of the common spinloop.
-         * This is useless but harmless on iSeries, secondaries are already
-         * waiting on their paca spinloops. */
+         */
 
         ptr  = (unsigned long *)((unsigned long)&__secondary_hold_spinloop
                         - PHYSICAL_START);
-        *ptr = 1;
+        *ptr = __pa(generic_secondary_smp_init);
         mb();
 
         DBG(" <- smp_release_cpus()\n");