target/arm/cpu64: max cpu: Introduce sve<N> properties

Introduce cpu properties to give fine control over SVE vector lengths.
We introduce a property for each valid length up to the current
maximum supported, which is 2048-bits. The properties are named, e.g.
sve128, sve256, sve384, sve512, ..., where the number is the number of
bits. See the updates to docs/arm-cpu-features.rst for a description
of the semantics and for example uses.

Note, as sve-max-vq is still present and we'd like to be able to
support qmp_query_cpu_model_expansion with guests launched with e.g.
-cpu max,sve-max-vq=8 on their command lines, then we do allow
sve-max-vq and sve<N> properties to be provided at the same time, but
this is not recommended, and is why sve-max-vq is not mentioned in the
document.  If sve-max-vq is provided then it enables all lengths smaller
than and including the max and disables all lengths larger. It also has
the side-effect that no larger lengths may be enabled and that the max
itself cannot be disabled. Smaller non-power-of-two lengths may,
however, be disabled, e.g. -cpu max,sve-max-vq=4,sve384=off provides a
guest the vector lengths 128, 256, and 512 bits.

This patch has been co-authored with Richard Henderson, who reworked
the target/arm/cpu64.c changes in order to push all the validation and
auto-enabling/disabling steps into the finalizer, resulting in a nice
LOC reduction.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Reviewed-by: Beata Michalska <beata.michalska@linaro.org>
Message-id: 20191031142734.8590-5-drjones@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 191 insertions, 1 deletions

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 89a8ae77fe..34b0ba2cf6 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -256,6 +256,151 @@ static void aarch64_a72_initfn(Object *obj)
     define_arm_cp_regs(cpu, cortex_a72_a57_a53_cp_reginfo);
 }
 
+void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp)
+{
+    /*
+     * If any vector lengths are explicitly enabled with sve<N> properties,
+     * then all other lengths are implicitly disabled.  If sve-max-vq is
+     * specified then it is the same as explicitly enabling all lengths
+     * up to and including the specified maximum, which means all larger
+     * lengths will be implicitly disabled.  If no sve<N> properties
+     * are enabled and sve-max-vq is not specified, then all lengths not
+     * explicitly disabled will be enabled.  Additionally, all power-of-two
+     * vector lengths less than the maximum enabled length will be
+     * automatically enabled and all vector lengths larger than the largest
+     * disabled power-of-two vector length will be automatically disabled.
+     * Errors are generated if the user provided input that interferes with
+     * any of the above.  Finally, if SVE is not disabled, then at least one
+     * vector length must be enabled.
+     */
+    DECLARE_BITMAP(tmp, ARM_MAX_VQ);
+    uint32_t vq, max_vq = 0;
+
+    /*
+     * Process explicit sve<N> properties.
+     * From the properties, sve_vq_map<N> implies sve_vq_init<N>.
+     * Check first for any sve<N> enabled.
+     */
+    if (!bitmap_empty(cpu->sve_vq_map, ARM_MAX_VQ)) {
+        max_vq = find_last_bit(cpu->sve_vq_map, ARM_MAX_VQ) + 1;
+
+        if (cpu->sve_max_vq && max_vq > cpu->sve_max_vq) {
+            error_setg(errp, "cannot enable sve%d", max_vq * 128);
+            error_append_hint(errp, "sve%d is larger than the maximum vector "
+                              "length, sve-max-vq=%d (%d bits)\n",
+                              max_vq * 128, cpu->sve_max_vq,
+                              cpu->sve_max_vq * 128);
+            return;
+        }
+
+        /* Propagate enabled bits down through required powers-of-two. */
+        for (vq = pow2floor(max_vq); vq >= 1; vq >>= 1) {
+            if (!test_bit(vq - 1, cpu->sve_vq_init)) {
+                set_bit(vq - 1, cpu->sve_vq_map);
+            }
+        }
+    } else if (cpu->sve_max_vq == 0) {
+        /*
+         * No explicit bits enabled, and no implicit bits from sve-max-vq.
+         */
+        if (!cpu_isar_feature(aa64_sve, cpu)) {
+            /* SVE is disabled and so are all vector lengths.  Good. */
+            return;
+        }
+
+        /* Disabling a power-of-two disables all larger lengths. */
+        if (test_bit(0, cpu->sve_vq_init)) {
+            error_setg(errp, "cannot disable sve128");
+            error_append_hint(errp, "Disabling sve128 results in all vector "
+                              "lengths being disabled.\n");
+            error_append_hint(errp, "With SVE enabled, at least one vector "
+                              "length must be enabled.\n");
+            return;
+        }
+        for (vq = 2; vq <= ARM_MAX_VQ; vq <<= 1) {
+            if (test_bit(vq - 1, cpu->sve_vq_init)) {
+                break;
+            }
+        }
+        max_vq = vq <= ARM_MAX_VQ ? vq - 1 : ARM_MAX_VQ;
+
+        bitmap_complement(cpu->sve_vq_map, cpu->sve_vq_init, max_vq);
+        max_vq = find_last_bit(cpu->sve_vq_map, max_vq) + 1;
+    }
+
+    /*
+     * Process the sve-max-vq property.
+     * Note that we know from the above that no bit above
+     * sve-max-vq is currently set.
+     */
+    if (cpu->sve_max_vq != 0) {
+        max_vq = cpu->sve_max_vq;
+
+        if (!test_bit(max_vq - 1, cpu->sve_vq_map) &&
+            test_bit(max_vq - 1, cpu->sve_vq_init)) {
+            error_setg(errp, "cannot disable sve%d", max_vq * 128);
+            error_append_hint(errp, "The maximum vector length must be "
+                              "enabled, sve-max-vq=%d (%d bits)\n",
+                              max_vq, max_vq * 128);
+            return;
+        }
+
+        /* Set all bits not explicitly set within sve-max-vq. */
+        bitmap_complement(tmp, cpu->sve_vq_init, max_vq);
+        bitmap_or(cpu->sve_vq_map, cpu->sve_vq_map, tmp, max_vq);
+    }
+
+    /*
+     * We should know what max-vq is now.  Also, as we're done
+     * manipulating sve-vq-map, we ensure any bits above max-vq
+     * are clear, just in case anybody looks.
+     */
+    assert(max_vq != 0);
+    bitmap_clear(cpu->sve_vq_map, max_vq, ARM_MAX_VQ - max_vq);
+
+    /* Ensure all required powers-of-two are enabled. */
+    for (vq = pow2floor(max_vq); vq >= 1; vq >>= 1) {
+        if (!test_bit(vq - 1, cpu->sve_vq_map)) {
+            error_setg(errp, "cannot disable sve%d", vq * 128);
+            error_append_hint(errp, "sve%d is required as it "
+                              "is a power-of-two length smaller than "
+                              "the maximum, sve%d\n",
+                              vq * 128, max_vq * 128);
+            return;
+        }
+    }
+
+    /*
+     * Now that we validated all our vector lengths, the only question
+     * left to answer is if we even want SVE at all.
+     */
+    if (!cpu_isar_feature(aa64_sve, cpu)) {
+        error_setg(errp, "cannot enable sve%d", max_vq * 128);
+        error_append_hint(errp, "SVE must be enabled to enable vector "
+                          "lengths.\n");
+        error_append_hint(errp, "Add sve=on to the CPU property list.\n");
+        return;
+    }
+
+    /* From now on sve_max_vq is the actual maximum supported length. */
+    cpu->sve_max_vq = max_vq;
+}
+
+uint32_t arm_cpu_vq_map_next_smaller(ARMCPU *cpu, uint32_t vq)
+{
+    uint32_t bitnum;
+
+    /*
+     * We allow vq == ARM_MAX_VQ + 1 to be input because the caller may want
+     * to find the maximum vq enabled, which may be ARM_MAX_VQ, but this
+     * function always returns the next smaller than the input.
+     */
+    assert(vq && vq <= ARM_MAX_VQ + 1);
+
+    bitnum = find_last_bit(cpu->sve_vq_map, vq - 1);
+    return bitnum == vq - 1 ? 0 : bitnum + 1;
+}
+
 static void cpu_max_get_sve_max_vq(Object *obj, Visitor *v, const char *name,
                                    void *opaque, Error **errp)
 {
@@ -287,6 +432,44 @@ static void cpu_max_set_sve_max_vq(Object *obj, Visitor *v, const char *name,
     error_propagate(errp, err);
 }
 
+static void cpu_arm_get_sve_vq(Object *obj, Visitor *v, const char *name,
+                               void *opaque, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+    uint32_t vq = atoi(&name[3]) / 128;
+    bool value;
+
+    /* All vector lengths are disabled when SVE is off. */
+    if (!cpu_isar_feature(aa64_sve, cpu)) {
+        value = false;
+    } else {
+        value = test_bit(vq - 1, cpu->sve_vq_map);
+    }
+    visit_type_bool(v, name, &value, errp);
+}
+
+static void cpu_arm_set_sve_vq(Object *obj, Visitor *v, const char *name,
+                               void *opaque, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+    uint32_t vq = atoi(&name[3]) / 128;
+    Error *err = NULL;
+    bool value;
+
+    visit_type_bool(v, name, &value, &err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+
+    if (value) {
+        set_bit(vq - 1, cpu->sve_vq_map);
+    } else {
+        clear_bit(vq - 1, cpu->sve_vq_map);
+    }
+    set_bit(vq - 1, cpu->sve_vq_init);
+}
+
 static void cpu_arm_get_sve(Object *obj, Visitor *v, const char *name,
                             void *opaque, Error **errp)
 {
@@ -323,6 +506,7 @@ static void cpu_arm_set_sve(Object *obj, Visitor *v, const char *name,
 static void aarch64_max_initfn(Object *obj)
 {
     ARMCPU *cpu = ARM_CPU(obj);
+    uint32_t vq;
 
     if (kvm_enabled()) {
         kvm_arm_set_cpu_features_from_host(cpu);
@@ -426,11 +610,17 @@ static void aarch64_max_initfn(Object *obj)
         cpu->dcz_blocksize = 7; /*  512 bytes */
 #endif
 
-        cpu->sve_max_vq = ARM_MAX_VQ;
         object_property_add(obj, "sve-max-vq", "uint32", cpu_max_get_sve_max_vq,
                             cpu_max_set_sve_max_vq, NULL, NULL, &error_fatal);
         object_property_add(obj, "sve", "bool", cpu_arm_get_sve,
                             cpu_arm_set_sve, NULL, NULL, &error_fatal);
+
+        for (vq = 1; vq <= ARM_MAX_VQ; ++vq) {
+            char name[8];
+            sprintf(name, "sve%d", vq * 128);
+            object_property_add(obj, name, "bool", cpu_arm_get_sve_vq,
+                                cpu_arm_set_sve_vq, NULL, NULL, &error_fatal);
+        }
     }
 }