Given there is no way to tell the guest if the size of the large
decrementer changes, it is not possible to migrate a guest between
machines where the decrementer size differs.
Add a command line option to disable the large decrementer for a guest
on boot. This means we will not advertise the availability of the large
decrementer to the guest and thus it won't try to use it.
This allows for a way for a guest to be started which will be compatible
with live migration to a system with a differing decrementer size
(assuming that system still implements the basic 32-bit decrementer
mode).
A required option is supplied to force large decrementer, qemu will fail
to start if the host doesn't support it. There is also a default option
where the large decrementer will be enabled/disabled based on the
capabilities of the hypervisor.
Signed-off-by: Suraj Jitindar Singh <sjitindarsi...@gmail.com>
---
hw/ppc/spapr.c | 59 +++++++++++++++++++++++++++++++++++++++++++++-----
hw/ppc/spapr_hcall.c | 4 +++-
include/hw/ppc/spapr.h | 1 +
3 files changed, 57 insertions(+), 7 deletions(-)
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 6f38939..4290dd8 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -558,12 +558,12 @@ static void spapr_populate_cpu_dt(CPUState *cs, void
*fdt, int offset,
/*
* We set this property to let the guest know that it can use the large
* decrementer and its width in bits. This means we must be on a processor
- * with a large decrementer and the hypervisor must support it. In TCG the
- * large decrementer is always supported, in KVM we check the hypervisor
- * capability.
+ * with a large decrementer, it must not have been disabled and the
+ * hypervisor must support it. In TCG the large decrementer is always
+ * supported, in KVM we check the hypervisor capability.
*/
- if (pcc->large_decr_bits && ((!kvm_enabled()) ||
- kvmppc_has_cap_large_decr())) {
+ if (pcc->large_decr_bits && (spapr->large_decr_support != -1) &&
+ ((!kvm_enabled()) || kvmppc_has_cap_large_decr())) {
_FDT((fdt_setprop_u32(fdt, offset, "ibm,dec-bits",
pcc->large_decr_bits)));
}
@@ -1344,6 +1344,11 @@ static void ppc_spapr_reset(void)
/* We have to do this after vcpus are created since it calls ioctls */
if (kvm_enabled()) {
kvmppc_check_cap_large_decr();
+
+ if ((spapr->large_decr_support == 1) && !kvmppc_has_cap_large_decr()) {
+ error_report("Large decrementer unsupported by hypervisor");
+ exit(1);
+ }
}
qemu_devices_reset();
@@ -1451,7 +1456,9 @@ static int spapr_import_large_decr_bits(sPAPRMachineState
*spapr)
CPUState *cs = CPU(cpu);
PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cs);
- if (kvm_enabled()) {
+ if (spapr->large_decr_support == -1) {
+ /* Large decrementer disabled on the command line */
+ } else if (kvm_enabled()) {
if (!kvmppc_has_cap_large_decr()) {
error_report("Host doesn't support large decrementer and guest
requires it");
return -EINVAL;
@@ -2554,6 +2561,37 @@ static void spapr_set_modern_hotplug_events(Object *obj,
bool value,
spapr->use_hotplug_event_source = value;
}
+static char *spapr_get_large_decr_support(Object *obj, Error **errp)
+{
+ sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+
+ switch (spapr->large_decr_support) {
+ case -1:
+ return g_strdup("disabled");
+ case 1:
+ return g_strdup("required");
+ default:
+ return g_strdup("default");
+ }
+}
+
+static void spapr_set_large_decr_support(Object *obj, const char *value,
+ Error **errp)
+{
+ sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+
+ if (!strncmp(value, "disabled", strlen("disabled"))) {
+ spapr->large_decr_support = -1;
+ } else if (!strncmp(value, "required", strlen("required"))) {
+ spapr->large_decr_support = 1;
+ } else if (!strncmp(value, "default", strlen("default"))) {
+ spapr->large_decr_support = 0;
+ } else {
+ error_report("Unknown large-decr-support specified '%s'", value);
+ exit(1);
+ }
+}
+
static void spapr_machine_initfn(Object *obj)
{
sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
@@ -2574,6 +2612,15 @@ static void spapr_machine_initfn(Object *obj)
" place of standard EPOW events when
possible"
" (required for memory hot-unplug
support)",
NULL);
+ object_property_add_str(obj, "large-decr-support",
+ spapr_get_large_decr_support,
+ spapr_set_large_decr_support, NULL);
+ object_property_set_description(obj, "large-decr-support",
+ "Specifies the level of large decrementer
support"
+ " {required - don't start if not available
"
+ "| disabled - disable the large
decrementer"
+ " | default - depend on hypervisor
support}"
+ , NULL);
}
static void spapr_machine_finalizefn(Object *obj)
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index c06421b..b4b22cb 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1096,7 +1096,9 @@ static void cas_enable_large_decr(PowerPCCPU *cpu,
sPAPRMachineState *spapr)
PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
bool guest_large_decr = false;
- if (cpu->compat_pvr) {
+ if (spapr->large_decr_support == -1) {
+ /* Large decrementer disabled on the command line */
+ } else if (cpu->compat_pvr) {
guest_large_decr = cpu->compat_pvr >= CPU_POWERPC_LOGICAL_3_00;
} else {
guest_large_decr = (cpu->env.spr[SPR_PVR] &
CPU_POWERPC_POWER_SERVER_MASK)
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 4ba9b89..65c5659 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -114,6 +114,7 @@ struct sPAPRMachineState {
/*< public >*/
char *kvm_type;
MemoryHotplugState hotplug_memory;
+ int large_decr_support; /* 1 -> required | 0 -> default | -1 -> disable */
const char *icp_type;
};
--
2.9.4
