spapr: Add support for time base offset migration

This allows guests to have a different timebase origin from the host.

This is needed for migration, where a guest can migrate from one host
to another and the two hosts might have a different timebase origin.
However, the timebase seen by the guest must not go backwards, and
should go forwards only by a small amount corresponding to the time
taken for the migration.

This is only supported for recent POWER hardware which has the TBU40
(timebase upper 40 bits) register. That includes POWER6, 7, 8 but not
970.

This adds kvm_access_one_reg() to access a special register which is not
in env->spr. This requires kvm_set_one_reg/kvm_get_one_reg patch.

The feature must be present in the host kernel.

This bumps vmstate_spapr::version_id and enables new vmstate_ppc_timebase
only for it. Since the vmstate_spapr::minimum_version_id remains
unchanged, migration from older QEMU is supported but without
vmstate_ppc_timebase.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 79 insertions, 0 deletions

diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index 71df471746..bec82cd7a9 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -29,9 +29,11 @@
 #include "sysemu/cpus.h"
 #include "hw/timer/m48t59.h"
 #include "qemu/log.h"
+#include "qemu/error-report.h"
 #include "hw/loader.h"
 #include "sysemu/kvm.h"
 #include "kvm_ppc.h"
+#include "trace.h"
 
 //#define PPC_DEBUG_IRQ
 //#define PPC_DEBUG_TB
@@ -49,6 +51,8 @@
 #  define LOG_TB(...) do { } while (0)
 #endif
 
+#define NSEC_PER_SEC    1000000000LL
+
 static void cpu_ppc_tb_stop (CPUPPCState *env);
 static void cpu_ppc_tb_start (CPUPPCState *env);
 
@@ -829,6 +833,81 @@ static void cpu_ppc_set_tb_clk (void *opaque, uint32_t freq)
     cpu_ppc_store_purr(cpu, 0x0000000000000000ULL);
 }
 
+static void timebase_pre_save(void *opaque)
+{
+    PPCTimebase *tb = opaque;
+    uint64_t ticks = cpu_get_real_ticks();
+    PowerPCCPU *first_ppc_cpu = POWERPC_CPU(first_cpu);
+
+    if (!first_ppc_cpu->env.tb_env) {
+        error_report("No timebase object");
+        return;
+    }
+
+    tb->time_of_the_day_ns = get_clock_realtime();
+    /*
+     * tb_offset is only expected to be changed by migration so
+     * there is no need to update it from KVM here
+     */
+    tb->guest_timebase = ticks + first_ppc_cpu->env.tb_env->tb_offset;
+}
+
+static int timebase_post_load(void *opaque, int version_id)
+{
+    PPCTimebase *tb_remote = opaque;
+    CPUState *cpu;
+    PowerPCCPU *first_ppc_cpu = POWERPC_CPU(first_cpu);
+    int64_t tb_off_adj, tb_off, ns_diff;
+    int64_t migration_duration_ns, migration_duration_tb, guest_tb, host_ns;
+    unsigned long freq;
+
+    if (!first_ppc_cpu->env.tb_env) {
+        error_report("No timebase object");
+        return -1;
+    }
+
+    freq = first_ppc_cpu->env.tb_env->tb_freq;
+    /*
+     * Calculate timebase on the destination side of migration.
+     * The destination timebase must be not less than the source timebase.
+     * We try to adjust timebase by downtime if host clocks are not
+     * too much out of sync (1 second for now).
+     */
+    host_ns = get_clock_realtime();
+    ns_diff = MAX(0, host_ns - tb_remote->time_of_the_day_ns);
+    migration_duration_ns = MIN(NSEC_PER_SEC, ns_diff);
+    migration_duration_tb = muldiv64(migration_duration_ns, freq, NSEC_PER_SEC);
+    guest_tb = tb_remote->guest_timebase + MIN(0, migration_duration_tb);
+
+    tb_off_adj = guest_tb - cpu_get_real_ticks();
+
+    tb_off = first_ppc_cpu->env.tb_env->tb_offset;
+    trace_ppc_tb_adjust(tb_off, tb_off_adj, tb_off_adj - tb_off,
+                        (tb_off_adj - tb_off) / freq);
+
+    /* Set new offset to all CPUs */
+    CPU_FOREACH(cpu) {
+        PowerPCCPU *pcpu = POWERPC_CPU(cpu);
+        pcpu->env.tb_env->tb_offset = tb_off_adj;
+    }
+
+    return 0;
+}
+
+const VMStateDescription vmstate_ppc_timebase = {
+    .name = "timebase",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .pre_save = timebase_pre_save,
+    .post_load = timebase_post_load,
+    .fields      = (VMStateField []) {
+        VMSTATE_UINT64(guest_timebase, PPCTimebase),
+        VMSTATE_INT64(time_of_the_day_ns, PPCTimebase),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
 /* Set up (once) timebase frequency (in Hz) */
 clk_setup_cb cpu_ppc_tb_init (CPUPPCState *env, uint32_t freq)
 {