[POWERPC] Implement SLB shadow buffer

This adds a shadow buffer for the SLBs and regsiters it with PHYP.
Only the bolted SLB entries (top 3) are shadowed.

The SLB shadow buffer tells the hypervisor what the kernel needs to
have in the SLB for the kernel to be able to function.  The hypervisor
can use this information to speed up partition context switches.

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

1 files changed, 33 insertions, 4 deletions

diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
index de0c8842415c..d3733912adb4 100644
--- a/arch/powerpc/mm/slb.c
+++ b/arch/powerpc/mm/slb.c
@@ -22,6 +22,8 @@
 #include <asm/paca.h>
 #include <asm/cputable.h>
 #include <asm/cacheflush.h>
+#include <asm/smp.h>
+#include <linux/compiler.h>
 
 #ifdef DEBUG
 #define DBG(fmt...) udbg_printf(fmt)
@@ -50,9 +52,32 @@ static inline unsigned long mk_vsid_data(unsigned long ea, unsigned long flags)
         return (get_kernel_vsid(ea) << SLB_VSID_SHIFT) | flags;
 }
 
-static inline void create_slbe(unsigned long ea, unsigned long flags,
-                               unsigned long entry)
+static inline void slb_shadow_update(unsigned long esid, unsigned long vsid,
+                                     unsigned long entry)
 {
+        /*
+         * Clear the ESID first so the entry is not valid while we are
+         * updating it.
+         */
+        get_slb_shadow()->save_area[entry].esid = 0;
+        barrier();
+        get_slb_shadow()->save_area[entry].vsid = vsid;
+        barrier();
+        get_slb_shadow()->save_area[entry].esid = esid;
+
+}
+
+static inline void create_shadowed_slbe(unsigned long ea, unsigned long flags,
+                                        unsigned long entry)
+{
+        /*
+         * Updating the shadow buffer before writing the SLB ensures
+         * we don't get a stale entry here if we get preempted by PHYP
+         * between these two statements.
+         */
+        slb_shadow_update(mk_esid_data(ea, entry), mk_vsid_data(ea, flags),
+                          entry);
+
         asm volatile("slbmte  %0,%1" :
                      : "r" (mk_vsid_data(ea, flags)),
                        "r" (mk_esid_data(ea, entry))
@@ -77,6 +102,10 @@ void slb_flush_and_rebolt(void)
         if ((ksp_esid_data & ESID_MASK) == PAGE_OFFSET)
                 ksp_esid_data &= ~SLB_ESID_V;
 
+        /* Only third entry (stack) may change here so only resave that */
+        slb_shadow_update(ksp_esid_data,
+                          mk_vsid_data(ksp_esid_data, lflags), 2);
+
         /* We need to do this all in asm, so we're sure we don't touch
          * the stack between the slbia and rebolting it. */
         asm volatile("isync\n"
@@ -209,9 +238,9 @@ void slb_initialize(void)
         asm volatile("isync":::"memory");
         asm volatile("slbmte  %0,%0"::"r" (0) : "memory");
         asm volatile("isync; slbia; isync":::"memory");
-        create_slbe(PAGE_OFFSET, lflags, 0);
+        create_shadowed_slbe(PAGE_OFFSET, lflags, 0);
 
-        create_slbe(VMALLOC_START, vflags, 1);
+        create_shadowed_slbe(VMALLOC_START, vflags, 1);
 
         /* We don't bolt the stack for the time being - we're in boot,
          * so the stack is in the bolted segment.  By the time it goes