@@ -90,6 +90,7 @@ static int cap_htm; /* Hardware transactional memory support */
static int cap_mmu_radix;
static int cap_mmu_hash_v3;
static int cap_resize_hpt;
+static int cap_ppc_pvr_compat;
static uint32_t debug_inst_opcode;
@@ -147,6 +148,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX);
cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3);
cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
+ /*
+ * Note: setting it to false because there is not such capability
+ * in KVM at this moment.
+ *
+ * TODO: call kvm_vm_check_extension() with the right capability
+ * after the kernel starts implementing it.*/
+ cap_ppc_pvr_compat = false;
if (!cap_interrupt_level) {
fprintf(stderr, "KVM: Couldn't find level irq capability. Expect the "
@@ -2785,3 +2793,29 @@ void kvmppc_update_sdr1(target_ulong sdr1)
run_on_cpu(cs, kvmppc_pivot_hpt_cpu, RUN_ON_CPU_TARGET_PTR(sdr1));
}
}
+
+/*
+ * This is a helper function to detect a post migration scenario
+ * in which a guest, running as KVM-HV, freezes in cpu_post_load because
+ * the guest kernel can't handle a PVR value other than the actual host
+ * PVR in KVM_SET_SREGS, even if pvr_match() returns true.
+ *
+ * If we don't have cap_ppc_pvr_compat and we're not running in PR
+ * (so, we're HV), return true. The workaround itself is done in
+ * cpu_post_load.
+ *
+ * The order here is important: we'll only check for KVM PR as a
+ * fallback if the guest kernel can't handle the situation itself.
+ * We need to avoid as much as possible querying the running KVM type
+ * in QEMU level.
+ */
+bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu)
+{
+ CPUState *cs = CPU(cpu);
+
+ if (cap_ppc_pvr_compat) {
+ return false;
+ }
+
+ return kvm_enabled() && !kvmppc_is_pr(cs->kvm_state);
+}
@@ -67,6 +67,7 @@ void kvmppc_check_papr_resize_hpt(Error **errp);
int kvmppc_resize_hpt_prepare(PowerPCCPU *cpu, target_ulong flags, int shift);
int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift);
void kvmppc_update_sdr1(target_ulong sdr1);
+bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu);
bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path);
@@ -9,6 +9,7 @@
#include "mmu-hash64.h"
#include "migration/cpu.h"
#include "qapi/error.h"
+#include "kvm_ppc.h"
static int cpu_load_old(QEMUFile *f, void *opaque, int version_id)
{
@@ -249,6 +250,27 @@ static int cpu_post_load(void *opaque, int version_id)
}
}
+ /*
+ * If we're running with KVM HV, there is a chance that the guest
+ * is running with KVM HV and its kernel does not have the
+ * capability of dealing with a different PVR other than this
+ * exact host PVR in KVM_SET_SREGS. If that happens, the
+ * guest freezes after migration.
+ *
+ * The function kvmppc_pvr_workaround_required does this verification
+ * by first checking if the kernel has the cap, returning true immediately
+ * if that is the case. Otherwise, it checks if we're running in KVM PR.
+ * If the guest kernel does not have the cap and we're not running KVM-PR
+ * (so, it is running KVM-HV), we need to ensure that KVM_SET_SREGS will
+ * receive the PVR it expects as a workaround.
+ *
+ */
+#if defined(CONFIG_KVM)
+ if (kvmppc_pvr_workaround_required(cpu)) {
+ env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
+ }
+#endif
+
env->lr = env->spr[SPR_LR];
env->ctr = env->spr[SPR_CTR];
cpu_write_xer(env, env->spr[SPR_XER]);
Commit d5fc133eed ("ppc: Rework CPU compatibility testing across migration") changed the way cpu_post_load behaves with the PVR setting, causing an unexpected bug in KVM-HV migrations between hosts that are compatible (POWER8 and POWER8E, for example). Even with pvr_match() returning true, the guest freezes right after cpu_post_load. The reason is that the guest kernel can't handle a different PVR value other that the running host in KVM_SET_SREGS. In [1] it was discussed the possibility of a new KVM capability that would indicate that the guest kernel can handle a different PVR in KVM_SET_SREGS. Even if such feature is implemented, there is still the problem with older kernels that will not have this capability and will fail to migrate. This patch implements a workaround for that scenario. If running with KVM, check if the guest kernel does not have the capability (named here as 'cap_ppc_pvr_compat'). If it doesn't, calls kvmppc_is_pr() to see if the guest is running in KVM-HV. If all this happens, set env->spr[SPR_PVR] to the same value as the current host PVR. This ensures that we allow migrations with 'close enough' PVRs to still work in KVM-HV but also makes the code ready for this new KVM capability when it is done. A new function called 'kvmppc_pvr_workaround_required' was created to encapsulate the conditions said above and to avoid calling too many kvm.c internals inside cpu_post_load. [1] https://lists.gnu.org/archive/html/qemu-ppc/2017-06/msg00503.html Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com> --- target/ppc/kvm.c | 34 ++++++++++++++++++++++++++++++++++ target/ppc/kvm_ppc.h | 1 + target/ppc/machine.c | 22 ++++++++++++++++++++++ 3 files changed, 57 insertions(+)