[PATCH v9 21/26] target/arm/kvm: add helper to test SYSREG props against a scratch vcpu

[Eric Auger <eric.auger@redhat.com>]

Add kvm_idreg_write_scratch_vcpu helper that will be used
by qmp_query_cpu_model_expansion code to test SYSREG settings
against a scratch vcpu. Indeed when the expansion code is called
the actual vcpu has not been initialized so we use a scratch vcpu.
This latter has been initialized with features taken from
legacy compositive options (EL2, SVE, ...). So the trial is
very close to the final setup.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 target/arm/kvm_arm.h    |  4 ++++
 target/arm/kvm-stub.c   |  7 ++++++
 target/arm/kvm.c        | 51 +++++++++++++++++++++++++++++++++++++++++
 target/arm/trace-events |  1 +
 4 files changed, 63 insertions(+)

diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index 2b3474cc36..bace69efed 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -14,6 +14,7 @@
 #include "qapi/qapi-types-misc-arm.h"
 #include "system/kvm.h"
 #include "target/arm/cpu-qom.h"
+#include "cpu-idregs.h"
 
 #define KVM_ARM_VGIC_V2   (1 << 0)
 #define KVM_ARM_VGIC_V3   (1 << 1)
@@ -250,4 +251,7 @@ void arm_gic_cap_kvm_probe(GICCapability *v2, GICCapability *v3);
  */
 char *kvm_print_register_name(uint64_t regidx);
 
+bool kvm_idreg_write_scratch_vcpu(ARMCPU *cpu, int cpufd,
+                                  ARM64SysRegField *field, uint64_t newfv,
+                                  Error **errp);
 #endif
diff --git a/target/arm/kvm-stub.c b/target/arm/kvm-stub.c
index 88cbe8d85c..8e6fae0a4d 100644
--- a/target/arm/kvm-stub.c
+++ b/target/arm/kvm-stub.c
@@ -119,3 +119,10 @@ char *kvm_print_register_name(uint64_t regidx)
 {
     g_assert_not_reached();
 }
+
+bool kvm_idreg_write_scratch_vcpu(ARMCPU *cpu, int cpufd,
+                                  ARM64SysRegField *field, uint64_t newfv,
+                                  Error **errp)
+{
+    g_assert_not_reached();
+}
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 537673177a..f7ca0e0250 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -447,6 +447,57 @@ static bool kvm_arm_vcpu_validate_sysreg(ARMCPU *cpu, ARM64SysRegField *field,
 #define KEY_TO_REG_IDX(key)     ((uint32_t)(((uint64_t)(key)) >> 8))
 #define KEY_TO_SHIFT(key)       ((uint8_t)(((uint64_t)(key)) & 0xFF))
 
+bool kvm_idreg_write_scratch_vcpu(ARMCPU *cpu, int cpufd,
+                                  ARM64SysRegField *field, uint64_t newfv,
+                                  Error **errp)
+{
+    uint64_t mask, old_reg_val, new_reg_val, oldfv;
+    struct kvm_one_reg reg;
+    int lower = field->shift;
+    int length = field->length;
+    int index = field->index;
+    uint64_t kidx;
+    int ret;
+
+    mask = MAKE_64BIT_MASK(lower, length);
+
+    if (!kvm_arm_vcpu_validate_sysreg(cpu, field, newfv, errp)) {
+        return false;
+    };
+
+    kidx = idregs_sysreg_to_kvm_reg(id_register_sysreg[index]);
+    ret = read_sys_reg64(cpufd, &old_reg_val, kidx);
+    if (ret) {
+        error_setg(errp, "failed to read the scratch vcpu value for field %s %m",
+                   field->name);
+        return false;
+    }
+    oldfv = (old_reg_val & mask) >> lower;
+
+    new_reg_val = old_reg_val & ~mask;
+    new_reg_val |= newfv << lower;
+
+    reg.id = kidx;
+    reg.addr = (uintptr_t)&new_reg_val;
+    ret = ioctl(cpufd, KVM_SET_ONE_REG, &reg);
+    if (ret) {
+        error_setg(errp, "failed to apply new value 0x%"PRIx64" for field %s "
+                   "(previous is 0x%"PRIx64"): %m", newfv, field->name, oldfv);
+        return false;
+    } else {
+        uint64_t check_val, actualfv;
+
+        ret = read_sys_reg64(cpufd, &check_val, kidx);
+        if (ret) {
+            error_setg(errp, "failed to read the new reg value: %m");
+            return false;
+        }
+        actualfv = (check_val & mask) >> lower;
+        trace_kvm_idreg_write_scratch_vcpu(field->name, oldfv, newfv, actualfv);
+    }
+    return true;
+}
+
 static void set_sysreg_prop(Object *obj, Visitor *v,
                             const char *name, void *opaque,
                             Error **errp)
diff --git a/target/arm/trace-events b/target/arm/trace-events
index 2a9cc67035..7a3f499a0e 100644
--- a/target/arm/trace-events
+++ b/target/arm/trace-events
@@ -21,6 +21,7 @@ set_sysreg_prop(const char *name, uint64_t old, uint64_t mask, uint64_t field_va
 apply_sysreg_prop(const char *reg_name, const char *field_name, uint64_t old, uint64_t current, uint64_t mask, uint64_t field_value, uint64_t new) "%s.%s old=0x%"PRIx64" current=0x%"PRIx64" mask=0x%"PRIx64" new field value=0x%"PRIx64" new=0x%"PRIx64
 nb_sysreg_props(const char *name, int count) "%s: %d SYSREG properties"
 unexpected_writable_reserved_field(const char *reg_name, const char *field_name, int lower, int upper) "Unexpected writable reserved field: %s.%s [%d,%d], skip it ..."
+kvm_idreg_write_scratch_vcpu(const char *name, uint64_t oldfv, uint64_t newfv, uint64_t actualfv) "successful dry-run for %s old=0x%"PRIx64" new=0x%"PRIx64" actual=0x%"PRIx64
 
 # cpu.c
 arm_cpu_reset(uint64_t mp_aff) "cpu %" PRIu64
-- 
2.53.0