target/ppc: Fix CPU reservation migration for record-replay

ppc only migrates reserve_addr, so the destination machine can get a
valid reservation with an incorrect reservation value of 0. Prior to
commit 392d328 ("target/ppc: Ensure stcx size matches larx"),
this could permit a stcx. to incorrectly succeed. That commit
inadvertently fixed that bug because the target machine starts with an
impossible reservation size of 0, so any stcx. will fail.

This behaviour is permitted by the ISA because reservation loss may
have implementation-dependent cause. What's more, with KVM machines it
is impossible save or reasonably restore reservation state. However if
the vmstate is being used for record-replay, the reservation must be
saved and restored exactly in order for execution from snapshot to
match the record.

This patch deprecates the existing incomplete reserve_addr vmstate,
and adds a new vmstate subsection with complete reservation state.
The new vmstate is needed only when record-replay mode is active.

Acked-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

target/ppc/cpu.h

@@ -1121,7 +1121,9 @@ struct CPUArchState {
     target_ulong reserve_addr;   /* Reservation address */
     target_ulong reserve_length; /* Reservation larx op size (bytes) */
     target_ulong reserve_val;    /* Reservation value */
+#if defined(TARGET_PPC64)
     target_ulong reserve_val2;
+#endif
 
     /* These are used in supervisor mode only */
     target_ulong msr;      /* machine state register */

target/ppc/machine.c

@@ -10,6 +10,7 @@
 #include "qemu/main-loop.h"
 #include "kvm_ppc.h"
 #include "power8-pmu.h"
+#include "sysemu/replay.h"
 
 static void post_load_update_msr(CPUPPCState *env)
 {
@@ -690,6 +691,27 @@ static const VMStateDescription vmstate_compat = {
     }
 };
 
+static bool reservation_needed(void *opaque)
+{
+    return (replay_mode != REPLAY_MODE_NONE);
+}
+
+static const VMStateDescription vmstate_reservation = {
+    .name = "cpu/reservation",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = reservation_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINTTL(env.reserve_addr, PowerPCCPU),
+        VMSTATE_UINTTL(env.reserve_length, PowerPCCPU),
+        VMSTATE_UINTTL(env.reserve_val, PowerPCCPU),
+#if defined(TARGET_PPC64)
+        VMSTATE_UINTTL(env.reserve_val2, PowerPCCPU),
+#endif
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 const VMStateDescription vmstate_ppc_cpu = {
     .name = "cpu",
     .version_id = 5,
@@ -711,8 +733,7 @@ const VMStateDescription vmstate_ppc_cpu = {
         VMSTATE_UINTTL_ARRAY(env.spr, PowerPCCPU, 1024),
         VMSTATE_UINT64(env.spe_acc, PowerPCCPU),
 
-        /* Reservation */
-        VMSTATE_UINTTL(env.reserve_addr, PowerPCCPU),
+        VMSTATE_UNUSED(sizeof(target_ulong)), /* was env.reserve_addr */
 
         /* Supervisor mode architected state */
         VMSTATE_UINTTL(env.msr, PowerPCCPU),
@@ -741,6 +762,7 @@ const VMStateDescription vmstate_ppc_cpu = {
         &vmstate_tlbemb,
         &vmstate_tlbmas,
         &vmstate_compat,
+        &vmstate_reservation,
         NULL
     }
 };

target/ppc/translate.c

@@ -77,7 +77,9 @@ static TCGv cpu_xer, cpu_so, cpu_ov, cpu_ca, cpu_ov32, cpu_ca32;
 static TCGv cpu_reserve;
 static TCGv cpu_reserve_length;
 static TCGv cpu_reserve_val;
+#if defined(TARGET_PPC64)
 static TCGv cpu_reserve_val2;
+#endif
 static TCGv cpu_fpscr;
 static TCGv_i32 cpu_access_type;
 
@@ -151,9 +153,11 @@ void ppc_translate_init(void)
     cpu_reserve_val = tcg_global_mem_new(cpu_env,
                                          offsetof(CPUPPCState, reserve_val),
                                          "reserve_val");
+#if defined(TARGET_PPC64)
     cpu_reserve_val2 = tcg_global_mem_new(cpu_env,
                                           offsetof(CPUPPCState, reserve_val2),
                                           "reserve_val2");
+#endif
 
     cpu_fpscr = tcg_global_mem_new(cpu_env,
                                    offsetof(CPUPPCState, fpscr), "fpscr");