qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Qemu-devel] [RFCv2 12/12] ppc: Rework CPU compatibility testing across


From: David Gibson
Subject: [Qemu-devel] [RFCv2 12/12] ppc: Rework CPU compatibility testing across migration
Date: Wed, 16 Nov 2016 09:17:55 +1100

Migrating between different CPU versions is quite complicated for ppc.
A long time ago, we ensure identical CPU versions at either end by checking
the PVR had the same value.  However, this breaks under KVM HV, because
we always have to use the host's PVR - it's not virtualized.  That would
mean we couldn't migrate between hosts with different PVRs, even if the
CPUs are close enough to compatible in practice (sometimes identical cores
with different surrounding logic have different PVRs, so this happens in
practice quite often).

So, we removed the PVR check, but instead checked that several flags
indicating supported instructions matched.  This turns out to be a bad
idea, because those instruction masks are not architected information, but
essentially a TCG implementation detail.  So changes to qemu internal CPU
modelling can break migration - this happened between qemu-2.6 and
qemu-2.7.

Modern server-class CPUs can be placed into compatibility modes.  Now that
we're handling those properly, we finally have the information to sanely
deal with CPU compatibility across migration.

This patch bumps the migration version number for the ppc CPU removing the
instruction mask field (and some other unwise VMSTATE_EQUAL checks), and
adding the compatibility PVR to the migration stream.

We consider the CPUs compatible for migration if:
    * The source was running in a compatibility mode which the destination
      supports
OR  * The source has a PVR matching the same qemu CPU class as the
      destination, either an exact match or an approximate match determined
      by the cpu class's pvr_match hook.

Signed-off-by: David Gibson <address@hidden>
---
 target-ppc/machine.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 79 insertions(+), 8 deletions(-)

diff --git a/target-ppc/machine.c b/target-ppc/machine.c
index e43cb6c..25a30d5 100644
--- a/target-ppc/machine.c
+++ b/target-ppc/machine.c
@@ -8,6 +8,7 @@
 #include "helper_regs.h"
 #include "mmu-hash64.h"
 #include "migration/cpu.h"
+#include "qapi/error.h"
 
 static int cpu_load_old(QEMUFile *f, void *opaque, int version_id)
 {
@@ -163,6 +164,30 @@ static void cpu_pre_save(void *opaque)
     }
 }
 
+/*
+ * Determine if a given PVR is a "close enough" match to the CPU
+ * object.  For TCG and KVM PR it would probably be sufficient to
+ * require an exact PVR match.  However for KVM HV the user is
+ * restricted to a PVR exactly matching the host CPU.  The correct way
+ * to handle this is to put the guest into an architected
+ * compatibility mode.  However, to allow a more forgiving transition
+ * and migration from before this was widely done, we allow migration
+ * between sufficiently similar PVRs, as determined by the CPU class's
+ * pvr_match() hook.
+ */
+static bool pvr_match(PowerPCCPU *cpu, uint32_t pvr)
+{
+    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
+
+    if (pvr == pcc->pvr) {
+        return true;
+    }
+    if (pcc->pvr_match) {
+        return pcc->pvr_match(pcc, pvr);
+    }
+    return false;
+}
+
 static int cpu_post_load(void *opaque, int version_id)
 {
     PowerPCCPU *cpu = opaque;
@@ -171,10 +196,31 @@ static int cpu_post_load(void *opaque, int version_id)
     target_ulong msr;
 
     /*
-     * We always ignore the source PVR. The user or management
-     * software has to take care of running QEMU in a compatible mode.
+     * If we're operating in compat mode, we should be ok as long as
+     * the destination supports the same compatiblity mode.
+     *
+     * Otherwise, however, we require that the destination has exactly
+     * the same CPU model as the source.
      */
-    env->spr[SPR_PVR] = env->spr_cb[SPR_PVR].default_value;
+
+#if defined(TARGET_PPC64)
+    if (cpu->compat_pvr) {
+        Error *local_err = NULL;
+
+        ppc_set_compat(cpu, cpu->compat_pvr, &local_err);
+        if (local_err) {
+            error_report_err(local_err);
+            error_free(local_err);
+            return -1;
+        }
+    } else
+#endif
+    {
+        if (!pvr_match(cpu, env->spr[SPR_PVR])) {
+            return -1;
+        }
+    }
+
     env->lr = env->spr[SPR_LR];
     env->ctr = env->spr[SPR_CTR];
     cpu_write_xer(env, env->spr[SPR_XER]);
@@ -527,9 +573,32 @@ static const VMStateDescription vmstate_tlbmas = {
     }
 };
 
+static bool compat_needed(void *opaque)
+{
+    PowerPCCPU *cpu = opaque;
+
+    return cpu->vhyp != NULL;
+}
+
+static const VMStateDescription vmstate_compat = {
+    .name = "cpu/compat",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = compat_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(compat_pvr, PowerPCCPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static bool version_before_6(void *opaque, int version_id)
+{
+    return version_id < 6;
+}
+
 const VMStateDescription vmstate_ppc_cpu = {
     .name = "cpu",
-    .version_id = 5,
+    .version_id = 6,
     .minimum_version_id = 5,
     .minimum_version_id_old = 4,
     .load_state_old = cpu_load_old,
@@ -561,10 +630,11 @@ const VMStateDescription vmstate_ppc_cpu = {
         /* FIXME: access_type? */
 
         /* Sanity checking */
-        VMSTATE_UINTTL_EQUAL(env.msr_mask, PowerPCCPU),
-        VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU),
-        VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU),
-        VMSTATE_UINT32_EQUAL(env.nb_BATs, PowerPCCPU),
+        VMSTATE_UNUSED_TEST(version_before_6,
+                            sizeof(target_ulong) /* msr_mask */
+                            + sizeof(uint64_t) /* insns_flags */
+                            + sizeof(uint64_t) /* insns_flags2 */
+                            + sizeof(uint32_t)), /* nb_BATs */
         VMSTATE_END_OF_LIST()
     },
     .subsections = (const VMStateDescription*[]) {
@@ -579,6 +649,7 @@ const VMStateDescription vmstate_ppc_cpu = {
         &vmstate_tlb6xx,
         &vmstate_tlbemb,
         &vmstate_tlbmas,
+        &vmstate_compat,
         NULL
     }
 };
-- 
2.7.4




reply via email to

[Prev in Thread] Current Thread [Next in Thread]