[Qemu-ppc] [PATCH -V3 1/4] target-ppc: Update slb array with correct index values.

[Aneesh Kumar K.V]

From: "Aneesh Kumar K.V" <address@hidden>

Without this, a value of rb=0 and rs=0 results in replacing the 0th
index. This can be observed when using gdb remote debugging support.

(gdb) x/10i do_fork
   0xc000000000085330 <do_fork>:        Cannot access memory at address 
0xc000000000085330
(gdb)

This is because when we do the slb sync via kvm_cpu_synchronize_state,
we overwrite the slb entry (0th entry) for 0xc000000000085330

Signed-off-by: Aneesh Kumar K.V <address@hidden>
---
 target-ppc/kvm.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 30a870e..6878af2 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -1033,9 +1033,25 @@ int kvm_arch_get_registers(CPUState *cs)
 
         /* Sync SLB */
 #ifdef TARGET_PPC64
+        /*
+         * KVM_GET_SREGS doesn't return slb entry with slot information
+         * same as index. The ioctl zero fills the array and update only
+         * upto slb_max entries. We cannot depend on the slot value
+         * in the slbe field for update, because a zero slbe value would
+         * result in us wrongly updating the 0th index. Instead we zero fill
+         * the env->slb array first so that we mark all entries invalid and
+         * update with only valid SLB entries.
+         */
+        memset(env->slb, 0, 64 * sizeof(ppc_slb_t));
         for (i = 0; i < 64; i++) {
-            ppc_store_slb(env, sregs.u.s.ppc64.slb[i].slbe,
-                               sregs.u.s.ppc64.slb[i].slbv);
+            target_ulong rb = sregs.u.s.ppc64.slb[i].slbe;
+            target_ulong rs = sregs.u.s.ppc64.slb[i].slbv;
+            /*
+             * Only restore valid entries
+             */
+            if (rb & SLB_ESID_V) {
+                ppc_store_slb(env, rb, rs);
+            }
         }
 #endif
 
-- 
1.8.1.2