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>

1 files changed, 5 insertions, 4 deletions

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");