powerpc/booke64: Use SPRG7 for VDSO

Previously SPRG3 was marked for use by both VDSO and critical
interrupts (though critical interrupts were not fully implemented).

In commit 8b64a9dfb091f1eca8b7e58da82f1e7d1d5fe0ad ("powerpc/booke64:
Use SPRG0/3 scratch for bolted TLB miss & crit int"), Mihai Caraman
made an attempt to resolve this conflict by restoring the VDSO value
early in the critical interrupt, but this has some issues:

 - It's incompatible with EXCEPTION_COMMON which restores r13 from the
   by-then-overwritten scratch (this cost me some debugging time).
 - It forces critical exceptions to be a special case handled
   differently from even machine check and debug level exceptions.
 - It didn't occur to me that it was possible to make this work at all
   (by doing a final "ld r13, PACA_EXCRIT+EX_R13(r13)") until after
   I made (most of) this patch. :-)

It might be worth investigating using a load rather than SPRG on return
from all exceptions (except TLB misses where the scratch never leaves
the SPRG) -- it could save a few cycles.  Until then, let's stick with
SPRG for all exceptions.

Since we cannot use SPRG4-7 for scratch without corrupting the state of
a KVM guest, move VDSO to SPRG7 on book3e.  Since neither SPRG4-7 nor
critical interrupts exist on book3s, SPRG3 is still used for VDSO
there.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Mihai Caraman <mihai.caraman@freescale.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: kvm-ppc@vger.kernel.org

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 094e45c..ce74c33 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -715,8 +715,8 @@ int vdso_getcpu_init(void)
 	unsigned long cpu, node, val;
 
 	/*
-	 * SPRG3 contains the CPU in the bottom 16 bits and the NUMA node in
-	 * the next 16 bits. The VDSO uses this to implement getcpu().
+	 * SPRG_VDSO contains the CPU in the bottom 16 bits and the NUMA node
+	 * in the next 16 bits.  The VDSO uses this to implement getcpu().
 	 */
 	cpu = get_cpu();
 	WARN_ON_ONCE(cpu > 0xffff);
@@ -725,8 +725,8 @@ int vdso_getcpu_init(void)
 	WARN_ON_ONCE(node > 0xffff);
 
 	val = (cpu & 0xfff) | ((node & 0xffff) << 16);
-	mtspr(SPRN_SPRG3, val);
-	get_paca()->sprg3 = val;
+	mtspr(SPRN_SPRG_VDSO_WRITE, val);
+	get_paca()->sprg_vdso = val;
 
 	put_cpu();