[POWERPC] Remove barriers from the SLB shadow buffer update

After talking to an IBM POWER hypervisor (PHYP) design and development
guy, there seems to be no need for memory barriers when updating the SLB
shadow buffer provided we only update it from the current CPU, which we
do.

Also, these guys see no need in the future for these barriers.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 952eba6..fbbd3f6 100644 (file)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -385,15 +385,15 @@ BEGIN_FTR_SECTION
        oris    r0,r6,(SLB_ESID_V)@h
        ori     r0,r0,(SLB_NUM_BOLTED-1)@l
 
-       /* Update the last bolted SLB */
+       /* Update the last bolted SLB.  No write barriers are needed
+        * here, provided we only update the current CPU's SLB shadow
+        * buffer.
+        */
        ld      r9,PACA_SLBSHADOWPTR(r13)
        li      r12,0
        std     r12,SLBSHADOW_STACKESID(r9) /* Clear ESID */
-       eieio
        std     r7,SLBSHADOW_STACKVSID(r9)  /* Save VSID */
-       eieio
        std     r0,SLBSHADOW_STACKESID(r9)  /* Save ESID */
-       eieio
 
        slbie   r6
        slbie   r6              /* Workaround POWER5 < DD2.1 issue */

diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index ff1811a..4bee1cf 100644 (file)
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -59,14 +59,12 @@ static inline void slb_shadow_update(unsigned long ea,
 {
        /*
         * Clear the ESID first so the entry is not valid while we are
-        * updating it.
+        * updating it.  No write barriers are needed here, provided
+        * we only update the current CPU's SLB shadow buffer.
         */
        get_slb_shadow()->save_area[entry].esid = 0;
-       smp_wmb();
        get_slb_shadow()->save_area[entry].vsid = mk_vsid_data(ea, flags);
-       smp_wmb();
        get_slb_shadow()->save_area[entry].esid = mk_esid_data(ea, entry);
-       smp_wmb();
 }
 
 static inline void slb_shadow_clear(unsigned long entry)