arm/kvm: report registers we failed to set

If we fail migration because of a mismatch of some registers between
source and destination, the error message is not very informative:

qemu-system-aarch64: error while loading state for instance 0x0 ofdevice 'cpu'
qemu-system-aarch64: Failed to put registers after init: Invalid argument

At least try to give the user a hint which registers had a problem,
even if they cannot really do anything about it right now.

Sample output:

Could not set register op0:3 op1:0 crn:0 crm:0 op2:0 to c00fac31 (is 413fd0c1)

We could be even more helpful once we support writable ID registers,
at which point the user might actually be able to configure something
that is migratable.

Suggested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Message-id: 20250911154159.158046-1-cohuck@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 667234485547a71c3da72c197629c45b215e6408..c1ec6654ca6774315bbad330bf90400a10c4b12f 100644 (file)
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -900,6 +900,58 @@ bool write_kvmstate_to_list(ARMCPU *cpu)
     return ok;
 }
 
+/* pretty-print a KVM register */
+#define CP_REG_ARM64_SYSREG_OP(_reg, _op)                       \
+    ((uint8_t)((_reg & CP_REG_ARM64_SYSREG_ ## _op ## _MASK) >> \
+               CP_REG_ARM64_SYSREG_ ## _op ## _SHIFT))
+
+static gchar *kvm_print_sve_register_name(uint64_t regidx)
+{
+    uint16_t sve_reg = regidx & 0x000000000000ffff;
+
+    if (regidx == KVM_REG_ARM64_SVE_VLS) {
+        return g_strdup_printf("SVE VLS");
+    }
+    /* zreg, preg, ffr */
+    switch (sve_reg & 0xfc00) {
+    case 0:
+        return g_strdup_printf("SVE zreg n:%d slice:%d",
+                               (sve_reg & 0x03e0) >> 5, sve_reg & 0x001f);
+    case 0x04:
+        return g_strdup_printf("SVE preg n:%d slice:%d",
+                               (sve_reg & 0x01e0) >> 5, sve_reg & 0x001f);
+    case 0x06:
+        return g_strdup_printf("SVE ffr slice:%d", sve_reg & 0x001f);
+    default:
+        return g_strdup_printf("SVE ???");
+    }
+}
+
+static gchar *kvm_print_register_name(uint64_t regidx)
+{
+        switch ((regidx & KVM_REG_ARM_COPROC_MASK)) {
+        case KVM_REG_ARM_CORE:
+            return g_strdup_printf("core reg %"PRIx64, regidx);
+        case KVM_REG_ARM_DEMUX:
+            return g_strdup_printf("demuxed reg %"PRIx64, regidx);
+        case KVM_REG_ARM64_SYSREG:
+            return g_strdup_printf("op0:%d op1:%d crn:%d crm:%d op2:%d",
+                                   CP_REG_ARM64_SYSREG_OP(regidx, OP0),
+                                   CP_REG_ARM64_SYSREG_OP(regidx, OP1),
+                                   CP_REG_ARM64_SYSREG_OP(regidx, CRN),
+                                   CP_REG_ARM64_SYSREG_OP(regidx, CRM),
+                                   CP_REG_ARM64_SYSREG_OP(regidx, OP2));
+        case KVM_REG_ARM_FW:
+            return g_strdup_printf("fw reg %d", (int)(regidx & 0xffff));
+        case KVM_REG_ARM64_SVE:
+            return kvm_print_sve_register_name(regidx);
+        case KVM_REG_ARM_FW_FEAT_BMAP:
+            return g_strdup_printf("fw feat reg %d", (int)(regidx & 0xffff));
+        default:
+            return g_strdup_printf("%"PRIx64, regidx);
+        }
+}
+
 bool write_list_to_kvmstate(ARMCPU *cpu, int level)
 {
     CPUState *cs = CPU(cpu);
@@ -927,11 +979,45 @@ bool write_list_to_kvmstate(ARMCPU *cpu, int level)
             g_assert_not_reached();
         }
         if (ret) {
+            gchar *reg_str = kvm_print_register_name(regidx);
+
             /* We might fail for "unknown register" and also for
              * "you tried to set a register which is constant with
              * a different value from what it actually contains".
              */
             ok = false;
+            switch (ret) {
+            case -ENOENT:
+                error_report("Could not set register %s: unknown to KVM",
+                             reg_str);
+                break;
+            case -EINVAL:
+                if ((regidx & KVM_REG_SIZE_MASK) == KVM_REG_SIZE_U32) {
+                    if (!kvm_get_one_reg(cs, regidx, &v32)) {
+                        error_report("Could not set register %s to %x (is %x)",
+                                     reg_str, (uint32_t)cpu->cpreg_values[i],
+                                     v32);
+                    } else {
+                        error_report("Could not set register %s to %x",
+                                     reg_str, (uint32_t)cpu->cpreg_values[i]);
+                    }
+                } else /* U64 */ {
+                    uint64_t v64;
+
+                    if (!kvm_get_one_reg(cs, regidx, &v64)) {
+                        error_report("Could not set register %s to %"PRIx64" (is %"PRIx64")",
+                                     reg_str, cpu->cpreg_values[i], v64);
+                    } else {
+                        error_report("Could not set register %s to %"PRIx64,
+                                     reg_str, cpu->cpreg_values[i]);
+                    }
+                }
+                break;
+            default:
+                error_report("Could not set register %s: %s",
+                             reg_str, strerror(-ret));
+            }
+            g_free(reg_str);
         }
     }
     return ok;