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, 10 insertions, 3 deletions

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index bf0fb4db0855..f7251c2dc049 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -577,9 +577,13 @@
 #define SPRN_SPRG3      0x113   /* Special Purpose Register General 3 */
 #define SPRN_USPRG3     0x103   /* SPRG3 userspace read */
 #define SPRN_SPRG4      0x114   /* Special Purpose Register General 4 */
+#define SPRN_USPRG4     0x104   /* SPRG4 userspace read */
 #define SPRN_SPRG5      0x115   /* Special Purpose Register General 5 */
+#define SPRN_USPRG5     0x105   /* SPRG5 userspace read */
 #define SPRN_SPRG6      0x116   /* Special Purpose Register General 6 */
+#define SPRN_USPRG6     0x106   /* SPRG6 userspace read */
 #define SPRN_SPRG7      0x117   /* Special Purpose Register General 7 */
+#define SPRN_USPRG7     0x107   /* SPRG7 userspace read */
 #define SPRN_SRR0       0x01A   /* Save/Restore Register 0 */
 #define SPRN_SRR1       0x01B   /* Save/Restore Register 1 */
 #define   SRR1_ISI_NOPT         0x40000000 /* ISI: Not found in hash */
@@ -879,11 +883,10 @@
  * 64-bit embedded
  *      - SPRG0 generic exception scratch
  *      - SPRG2 TLB exception stack
- *      - SPRG3 critical exception scratch and
- *        CPU and NUMA node for VDSO getcpu (user visible)
+ *      - SPRG3 critical exception scratch (user visible, sorry!)
  *      - SPRG4 unused (user visible)
  *      - SPRG6 TLB miss scratch (user visible, sorry !)
- *      - SPRG7 critical exception scratch
+ *      - SPRG7 CPU and NUMA node for VDSO getcpu (user visible)
  *      - SPRG8 machine check exception scratch
  *      - SPRG9 debug exception scratch
  *
@@ -940,6 +943,8 @@
 #define SPRN_SPRG_SCRATCH0      SPRN_SPRG2
 #define SPRN_SPRG_HPACA         SPRN_HSPRG0
 #define SPRN_SPRG_HSCRATCH0     SPRN_HSPRG1
+#define SPRN_SPRG_VDSO_READ     SPRN_USPRG3
+#define SPRN_SPRG_VDSO_WRITE    SPRN_SPRG3
 
 #define GET_PACA(rX)                                    \
         BEGIN_FTR_SECTION_NESTED(66);                   \
@@ -983,6 +988,8 @@
 #define SPRN_SPRG_TLB_SCRATCH   SPRN_SPRG6
 #define SPRN_SPRG_GEN_SCRATCH   SPRN_SPRG0
 #define SPRN_SPRG_GDBELL_SCRATCH SPRN_SPRG_GEN_SCRATCH
+#define SPRN_SPRG_VDSO_READ     SPRN_USPRG7
+#define SPRN_SPRG_VDSO_WRITE    SPRN_SPRG7
 
 #define SET_PACA(rX)    mtspr   SPRN_SPRG_PACA,rX
 #define GET_PACA(rX)    mfspr   rX,SPRN_SPRG_PACA