target/arm/cpu: Introduce the infrastructure for cpreg migration tolerances

We introduce a datatype for a tolerance with respect to a given
cpreg migration issue. The tolerance applies to a given cpreg kvm index,
and can be of different types:
a) mismatch in cpreg indexes
- ToleranceNotOnBothEnds (cpreg index is allowed to be only present
  on one end)
- ToleranceOnlySrcTestValue (cpreg index is allowed to be only
  present in source if its value @mask field matches @value)
b) mismatch in cpreg values
- ToleranceDiffInMask (value differences are allowed only within a mask)
- ToleranceFieldLT (incoming field value must be less than a given value)
- ToleranceFieldGT (incoming field value must be greater than a given value)

A QLIST of such tolerances can be populated using a new helper:
arm_register_cpreg_mig_tolerance() and arm_cpu_match_cpreg_mig_tolerance()
allows to check whether a tolerance exists for a given kvm index and its
criterion is matched.

callers for those helpers will be introduced in subsequent patches.

Only registration of migration tolerances related to cpreg index
mismatch is currently allowed.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20260420140552.104369-2-eric.auger@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 9b80dda140ad90e522d46ed34e2aa4b79b8907b2..10feb639c4d397bcff1d914450642dd610cb02d4 100644 (file)
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -181,6 +181,82 @@ void arm_register_el_change_hook(ARMCPU *cpu, ARMELChangeHookFn *hook,
     QLIST_INSERT_HEAD(&cpu->el_change_hooks, entry, node);
 }
 
+static ARMCPRegMigTolerance *find_mig_tolerance(ARMCPU *cpu, uint64_t kvmidx)
+{
+    ARMCPRegMigTolerance *t;
+    QLIST_FOREACH(t, &cpu->cpreg_mig_tolerances, node) {
+        if (t->kvmidx == kvmidx)  {
+            return t;
+        }
+    }
+    return NULL;
+}
+
+void arm_register_cpreg_mig_tolerance(ARMCPU *cpu, uint64_t kvmidx,
+                                      uint64_t mask, uint64_t value,
+                                      ARMCPRegMigToleranceType type)
+{
+    ARMCPRegMigTolerance *entry;
+
+    /* make sure the kvmidx has not tolerance already registered */
+    assert(!find_mig_tolerance(cpu, kvmidx));
+
+    assert(type == ToleranceNotOnBothEnds ||
+           type == ToleranceOnlySrcTestValue);
+
+    entry = g_new0(ARMCPRegMigTolerance, 1);
+
+    entry->kvmidx = kvmidx;
+    entry->mask = mask;
+    entry->value = value;
+    entry->type = type;
+
+    QLIST_INSERT_HEAD(&cpu->cpreg_mig_tolerances, entry, node);
+}
+
+bool arm_cpu_match_cpreg_mig_tolerance(ARMCPU *cpu, uint64_t kvmidx,
+                                       uint64_t vmstate_value, uint64_t local_value,
+                                       ARMCPRegMigToleranceType type)
+{
+    ARMCPRegMigTolerance *t = find_mig_tolerance(cpu, kvmidx);
+    uint64_t diff, diff_outside_mask, field;
+
+    if (!t || t->type != type) {
+        return false;
+    }
+
+    if (type == ToleranceNotOnBothEnds) {
+        return true;
+    }
+
+    if (type == ToleranceOnlySrcTestValue &&
+        ((vmstate_value & t->mask) == t->value)) {
+        return true;
+    }
+
+    /* Need to check the mask */
+    diff = vmstate_value ^ local_value;
+    diff_outside_mask = diff & ~t->mask;
+
+    if (diff_outside_mask) {
+        /* there are differences outside of the mask */
+        return false;
+    }
+    if (type == ToleranceDiffInMask) {
+        /* differences only in the field, tolerance matched */
+        return true;
+    }
+    /* need to compare field value against authorized ones */
+    field = vmstate_value & t->mask;
+    if (type == ToleranceFieldLT && (field < t->value)) {
+        return true;
+    }
+    if (type == ToleranceFieldGT && (field > t->value)) {
+        return true;
+    }
+    return false;
+}
+
 static void cp_reg_reset(gpointer key, gpointer value, gpointer opaque)
 {
     /* Reset a single ARMCPRegInfo register */
@@ -1102,6 +1178,7 @@ static void arm_cpu_initfn(Object *obj)
 
     QLIST_INIT(&cpu->pre_el_change_hooks);
     QLIST_INIT(&cpu->el_change_hooks);
+    QLIST_INIT(&cpu->cpreg_mig_tolerances);
 
 #ifdef CONFIG_USER_ONLY
 # ifdef TARGET_AARCH64
@@ -1574,6 +1651,7 @@ static void arm_cpu_finalizefn(Object *obj)
 {
     ARMCPU *cpu = ARM_CPU(obj);
     ARMELChangeHook *hook, *next;
+    ARMCPRegMigTolerance *t, *n;
 
     g_hash_table_destroy(cpu->cp_regs);
 
@@ -1585,6 +1663,10 @@ static void arm_cpu_finalizefn(Object *obj)
         QLIST_REMOVE(hook, node);
         g_free(hook);
     }
+    QLIST_FOREACH_SAFE(t, &cpu->cpreg_mig_tolerances, node, n) {
+        QLIST_REMOVE(t, node);
+        g_free(t);
+    }
 #ifndef CONFIG_USER_ONLY
     if (cpu->pmu_timer) {
         timer_free(cpu->pmu_timer);

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index ab6bacf4aa87aba2c8c315249e18891a9542c42e..be14a47c3574dad482f7a02a13a03a876d10ca22 100644 (file)
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -1140,6 +1140,7 @@ struct ArchCPU {
 
     QLIST_HEAD(, ARMELChangeHook) pre_el_change_hooks;
     QLIST_HEAD(, ARMELChangeHook) el_change_hooks;
+    QLIST_HEAD(, ARMCPRegMigTolerance) cpreg_mig_tolerances;
 
     int32_t node_id; /* NUMA node this CPU belongs to */
 

diff --git a/target/arm/internals.h b/target/arm/internals.h
index 06655409e500d31d0382e039d8bddc4974d56bef..a632584a4e0a89b9f4e0f20b34bca82b6e86b711 100644 (file)
--- a/target/arm/internals.h
+++ b/target/arm/internals.h
@@ -1943,4 +1943,58 @@ int compare_u64(const void *a, const void *b);
 /* Used in FEAT_MEC to set the MECIDWidthm1 field in the MECIDR_EL2 register. */
 #define MECID_WIDTH 16
 
+typedef enum {
+    ToleranceNotOnBothEnds,
+    ToleranceOnlySrcTestValue,
+    ToleranceDiffInMask,
+    ToleranceFieldLT,
+    ToleranceFieldGT,
+} ARMCPRegMigToleranceType;
+
+typedef struct ARMCPRegMigTolerance {
+    uint64_t kvmidx;
+    uint64_t mask;
+    uint64_t value;
+    ARMCPRegMigToleranceType type;
+    QLIST_ENTRY(ARMCPRegMigTolerance) node;
+} ARMCPRegMigTolerance;
+
+/**
+ * arm_register_cpreg_mig_tolerance:
+ * Register a migration tolerance wrt one given cpreg identified by its
+ * @kvmidx. Calling this function twice for the same @kvmidx is a
+ * programming error and will cause an assertion failure.
+ *
+ * @cpu: vcpu to apply the migration tolerance on
+ * @kvmidx: kvm index of the cpreg the tolerance applies to
+ * @mask: bitmask where a difference is tolerated
+ *        (relevant with ToleranceDiffInMask)
+ * @value: value the bitmask field is compared with
+ *        (relevant with ToleranceFieldLT and ToleranceFieldGT)
+ * @type: type of the migration tolerance:
+ * - ToleranceNotOnBothEnds (cpreg index is allowed to be only present
+ *   on one end)
+ * - ToleranceOnlySrcTestValue (cpreg index is allowed to be only
+ *   present in source if its value @mask field matches @value)
+ * - ToleranceDiffInMask (mismatch in cpreg values are only tolerated
+ *   if differences are within @mask)
+ * - ToleranceFieldLT (mismatch in cpreg values are only tolerated
+ *   if incoming @bitmask field value is less than @value)
+ * - ToleranceFieldGT (mismatch in cpreg values are only tolerated
+ *   if incoming @bitmask field value is greater than @value)
+ */
+void arm_register_cpreg_mig_tolerance(ARMCPU *cpu, uint64_t kvmidx,
+                                      uint64_t mask, uint64_t value,
+                                      ARMCPRegMigToleranceType type);
+
+/**
+ * arm_cpu_match_cpreg_mig_tolerance:
+ * Check whether a tolerance of type @type exists for a given @kvmidx
+ * and the tolerance criterion is satisfied
+ */
+bool arm_cpu_match_cpreg_mig_tolerance(ARMCPU *cpu, uint64_t kvmidx,
+                                       uint64_t vmstate_value, uint64_t local_value,
+                                       ARMCPRegMigToleranceType type);
+
+
 #endif