[PULL,24/35] spapr: Fix record-replay machine reset consuming too many events

Commit Message

Cédric Le Goater Sept. 4, 2023, 9:06 a.m. UTC

From: Nicholas Piggin <[e-mail]>

spapr_machine_reset gets a random number to populate the device-tree
rng seed with. When loading a snapshot for record-replay, the machine
is reset again, and that tries to consume the random event record
again, crashing due to inconsistent record

Fix this by saving the seed to populate the device tree with, and
skipping the rng on snapshot load.

Acked-by: Pavel Dovgalyuk <[e-mail]>
Signed-off-by: Nicholas Piggin <[e-mail]>
Signed-off-by: Cédric Le Goater <[e-mail]>
---
 include/hw/ppc/spapr.h |  1 +
 hw/ppc/spapr.c         | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

Patch

diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index f47e8419a575..f4bd204d8633 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -204,6 +204,7 @@  struct SpaprMachineState {
     uint32_t fdt_size;
     uint32_t fdt_initial_size;
     void *fdt_blob;
+    uint8_t fdt_rng_seed[32];
     long kernel_size;
     bool kernel_le;
     uint64_t kernel_addr;
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index c0b0ada121f9..f7cc6a890f45 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1022,7 +1022,6 @@  static void spapr_dt_chosen(SpaprMachineState *spapr, void *fdt, bool reset)
 {
     MachineState *machine = MACHINE(spapr);
     SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
-    uint8_t rng_seed[32];
     int chosen;
 
     _FDT(chosen = fdt_add_subnode(fdt, 0, "chosen"));
@@ -1100,8 +1099,7 @@  static void spapr_dt_chosen(SpaprMachineState *spapr, void *fdt, bool reset)
         spapr_dt_ov5_platform_support(spapr, fdt, chosen);
     }
 
-    qemu_guest_getrandom_nofail(rng_seed, sizeof(rng_seed));
-    _FDT(fdt_setprop(fdt, chosen, "rng-seed", rng_seed, sizeof(rng_seed)));
+    _FDT(fdt_setprop(fdt, chosen, "rng-seed", spapr->fdt_rng_seed, 32));
 
     _FDT(spapr_dt_ovec(fdt, chosen, spapr->ov5_cas, "ibm,architecture-vec-5"));
 }
@@ -1654,6 +1652,14 @@  static void spapr_machine_reset(MachineState *machine, ShutdownCause reason)
     void *fdt;
     int rc;
 
+    if (reason != SHUTDOWN_CAUSE_SNAPSHOT_LOAD) {
+        /*
+         * Record-replay snapshot load must not consume random, this was
+         * already replayed from initial machine reset.
+         */
+        qemu_guest_getrandom_nofail(spapr->fdt_rng_seed, 32);
+    }
+
     pef_kvm_reset(machine->cgs, &error_fatal);
     spapr_caps_apply(spapr);