arch/arm64/kvm/psci.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2012 - ARM Ltd
   4  * Author: Marc Zyngier <[email protected]>
   5  */
   6
   7 #include <linux/arm-smccc.h>
   8 #include <linux/preempt.h>
   9 #include <linux/kvm_host.h>
  10 #include <linux/uaccess.h>
  11 #include <linux/wait.h>
  12
  13 #include <asm/cputype.h>
  14 #include <asm/kvm_emulate.h>
  15
  16 #include <kvm/arm_psci.h>
  17 #include <kvm/arm_hypercalls.h>
  18
  19 /*
  20  * This is an implementation of the Power State Coordination Interface
  21  * as described in ARM document number ARM DEN 0022A.
  22  */
  23
  24 #define AFFINITY_MASK(level)    ~((0x1UL << ((level) * MPIDR_LEVEL_BITS)) - 1)
  25
  26 static unsigned long psci_affinity_mask(unsigned long affinity_level)
  27 {
  28         if (affinity_level <= 3)
  29                 return MPIDR_HWID_BITMASK & AFFINITY_MASK(affinity_level);
  30
  31         return 0;
  32 }
  33
  34 static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
  35 {
  36         /*
  37          * NOTE: For simplicity, we make VCPU suspend emulation to be
  38          * same-as WFI (Wait-for-interrupt) emulation.
  39          *
  40          * This means for KVM the wakeup events are interrupts and
  41          * this is consistent with intended use of StateID as described
  42          * in section 5.4.1 of PSCI v0.2 specification (ARM DEN 0022A).
  43          *
  44          * Further, we also treat power-down request to be same as
  45          * stand-by request as-per section 5.4.2 clause 3 of PSCI v0.2
  46          * specification (ARM DEN 0022A). This means all suspend states
  47          * for KVM will preserve the register state.
  48          */
  49         kvm_vcpu_halt(vcpu);
  50         kvm_clear_request(KVM_REQ_UNHALT, vcpu);
  51
  52         return PSCI_RET_SUCCESS;
  53 }
  54
  55 static void kvm_psci_vcpu_off(struct kvm_vcpu *vcpu)
  56 {
  57         vcpu->arch.power_off = true;
  58         kvm_make_request(KVM_REQ_SLEEP, vcpu);
  59         kvm_vcpu_kick(vcpu);
  60 }
  61
  62 static inline bool kvm_psci_valid_affinity(struct kvm_vcpu *vcpu,
  63                                            unsigned long affinity)
  64 {
  65         return !(affinity & ~MPIDR_HWID_BITMASK);
  66 }
  67
  68 static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
  69 {
  70         struct vcpu_reset_state *reset_state;
  71         struct kvm *kvm = source_vcpu->kvm;
  72         struct kvm_vcpu *vcpu = NULL;
  73         unsigned long cpu_id;
  74
  75         cpu_id = smccc_get_arg1(source_vcpu);
  76         if (!kvm_psci_valid_affinity(source_vcpu, cpu_id))
  77                 return PSCI_RET_INVALID_PARAMS;
  78
  79         vcpu = kvm_mpidr_to_vcpu(kvm, cpu_id);
  80
  81         /*
  82          * Make sure the caller requested a valid CPU and that the CPU is
  83          * turned off.
  84          */
  85         if (!vcpu)
  86                 return PSCI_RET_INVALID_PARAMS;
  87         if (!vcpu->arch.power_off) {
  88                 if (kvm_psci_version(source_vcpu, kvm) != KVM_ARM_PSCI_0_1)
  89                         return PSCI_RET_ALREADY_ON;
  90                 else
  91                         return PSCI_RET_INVALID_PARAMS;
  92         }
  93
  94         reset_state = &vcpu->arch.reset_state;
  95
  96         reset_state->pc = smccc_get_arg2(source_vcpu);
  97
  98         /* Propagate caller endianness */
  99         reset_state->be = kvm_vcpu_is_be(source_vcpu);
 100
 101         /*
 102          * NOTE: We always update r0 (or x0) because for PSCI v0.1
 103          * the general purpose registers are undefined upon CPU_ON.
 104          */
 105         reset_state->r0 = smccc_get_arg3(source_vcpu);
 106
 107         WRITE_ONCE(reset_state->reset, true);
 108         kvm_make_request(KVM_REQ_VCPU_RESET, vcpu);
 109
 110         /*
 111          * Make sure the reset request is observed if the change to
 112          * power_off is observed.
 113          */
 114         smp_wmb();
 115
 116         vcpu->arch.power_off = false;
 117         kvm_vcpu_wake_up(vcpu);
 118
 119         return PSCI_RET_SUCCESS;
 120 }
 121
 122 static unsigned long kvm_psci_vcpu_affinity_info(struct kvm_vcpu *vcpu)
 123 {
 124         int matching_cpus = 0;
 125         unsigned long i, mpidr;
 126         unsigned long target_affinity;
 127         unsigned long target_affinity_mask;
 128         unsigned long lowest_affinity_level;
 129         struct kvm *kvm = vcpu->kvm;
 130         struct kvm_vcpu *tmp;
 131
 132         target_affinity = smccc_get_arg1(vcpu);
 133         lowest_affinity_level = smccc_get_arg2(vcpu);
 134
 135         if (!kvm_psci_valid_affinity(vcpu, target_affinity))
 136                 return PSCI_RET_INVALID_PARAMS;
 137
 138         /* Determine target affinity mask */
 139         target_affinity_mask = psci_affinity_mask(lowest_affinity_level);
 140         if (!target_affinity_mask)
 141                 return PSCI_RET_INVALID_PARAMS;
 142
 143         /* Ignore other bits of target affinity */
 144         target_affinity &= target_affinity_mask;
 145
 146         /*
 147          * If one or more VCPU matching target affinity are running
 148          * then ON else OFF
 149          */
 150         kvm_for_each_vcpu(i, tmp, kvm) {
 151                 mpidr = kvm_vcpu_get_mpidr_aff(tmp);
 152                 if ((mpidr & target_affinity_mask) == target_affinity) {
 153                         matching_cpus++;
 154                         if (!tmp->arch.power_off)
 155                                 return PSCI_0_2_AFFINITY_LEVEL_ON;
 156                 }
 157         }
 158
 159         if (!matching_cpus)
 160                 return PSCI_RET_INVALID_PARAMS;
 161
 162         return PSCI_0_2_AFFINITY_LEVEL_OFF;
 163 }
 164
 165 static void kvm_prepare_system_event(struct kvm_vcpu *vcpu, u32 type)
 166 {
 167         unsigned long i;
 168         struct kvm_vcpu *tmp;
 169
 170         /*
 171          * The KVM ABI specifies that a system event exit may call KVM_RUN
 172          * again and may perform shutdown/reboot at a later time that when the
 173          * actual request is made.  Since we are implementing PSCI and a
 174          * caller of PSCI reboot and shutdown expects that the system shuts
 175          * down or reboots immediately, let's make sure that VCPUs are not run
 176          * after this call is handled and before the VCPUs have been
 177          * re-initialized.
 178          */
 179         kvm_for_each_vcpu(i, tmp, vcpu->kvm)
 180                 tmp->arch.power_off = true;
 181         kvm_make_all_cpus_request(vcpu->kvm, KVM_REQ_SLEEP);
 182
 183         memset(&vcpu->run->system_event, 0, sizeof(vcpu->run->system_event));
 184         vcpu->run->system_event.type = type;
 185         vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
 186 }
 187
 188 static void kvm_psci_system_off(struct kvm_vcpu *vcpu)
 189 {
 190         kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_SHUTDOWN);
 191 }
 192
 193 static void kvm_psci_system_reset(struct kvm_vcpu *vcpu)
 194 {
 195         kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET);
 196 }
 197
 198 static void kvm_psci_narrow_to_32bit(struct kvm_vcpu *vcpu)
 199 {
 200         int i;
 201
 202         /*
 203          * Zero the input registers' upper 32 bits. They will be fully
 204          * zeroed on exit, so we're fine changing them in place.
 205          */
 206         for (i = 1; i < 4; i++)
 207                 vcpu_set_reg(vcpu, i, lower_32_bits(vcpu_get_reg(vcpu, i)));
 208 }
 209
 210 static unsigned long kvm_psci_check_allowed_function(struct kvm_vcpu *vcpu, u32 fn)
 211 {
 212         switch(fn) {
 213         case PSCI_0_2_FN64_CPU_SUSPEND:
 214         case PSCI_0_2_FN64_CPU_ON:
 215         case PSCI_0_2_FN64_AFFINITY_INFO:
 216                 /* Disallow these functions for 32bit guests */
 217                 if (vcpu_mode_is_32bit(vcpu))
 218                         return PSCI_RET_NOT_SUPPORTED;
 219                 break;
 220         }
 221
 222         return 0;
 223 }
 224
 225 static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 226 {
 227         struct kvm *kvm = vcpu->kvm;
 228         u32 psci_fn = smccc_get_function(vcpu);
 229         unsigned long val;
 230         int ret = 1;
 231
 232         val = kvm_psci_check_allowed_function(vcpu, psci_fn);
 233         if (val)
 234                 goto out;
 235
 236         switch (psci_fn) {
 237         case PSCI_0_2_FN_PSCI_VERSION:
 238                 /*
 239                  * Bits[31:16] = Major Version = 0
 240                  * Bits[15:0] = Minor Version = 2
 241                  */
 242                 val = KVM_ARM_PSCI_0_2;
 243                 break;
 244         case PSCI_0_2_FN_CPU_SUSPEND:
 245         case PSCI_0_2_FN64_CPU_SUSPEND:
 246                 val = kvm_psci_vcpu_suspend(vcpu);
 247                 break;
 248         case PSCI_0_2_FN_CPU_OFF:
 249                 kvm_psci_vcpu_off(vcpu);
 250                 val = PSCI_RET_SUCCESS;
 251                 break;
 252         case PSCI_0_2_FN_CPU_ON:
 253                 kvm_psci_narrow_to_32bit(vcpu);
 254                 fallthrough;
 255         case PSCI_0_2_FN64_CPU_ON:
 256                 mutex_lock(&kvm->lock);
 257                 val = kvm_psci_vcpu_on(vcpu);
 258                 mutex_unlock(&kvm->lock);
 259                 break;
 260         case PSCI_0_2_FN_AFFINITY_INFO:
 261                 kvm_psci_narrow_to_32bit(vcpu);
 262                 fallthrough;
 263         case PSCI_0_2_FN64_AFFINITY_INFO:
 264                 val = kvm_psci_vcpu_affinity_info(vcpu);
 265                 break;
 266         case PSCI_0_2_FN_MIGRATE_INFO_TYPE:
 267                 /*
 268                  * Trusted OS is MP hence does not require migration
 269                  * or
 270                  * Trusted OS is not present
 271                  */
 272                 val = PSCI_0_2_TOS_MP;
 273                 break;
 274         case PSCI_0_2_FN_SYSTEM_OFF:
 275                 kvm_psci_system_off(vcpu);
 276                 /*
 277                  * We shouldn't be going back to guest VCPU after
 278                  * receiving SYSTEM_OFF request.
 279                  *
 280                  * If user space accidentally/deliberately resumes
 281                  * guest VCPU after SYSTEM_OFF request then guest
 282                  * VCPU should see internal failure from PSCI return
 283                  * value. To achieve this, we preload r0 (or x0) with
 284                  * PSCI return value INTERNAL_FAILURE.
 285                  */
 286                 val = PSCI_RET_INTERNAL_FAILURE;
 287                 ret = 0;
 288                 break;
 289         case PSCI_0_2_FN_SYSTEM_RESET:
 290                 kvm_psci_system_reset(vcpu);
 291                 /*
 292                  * Same reason as SYSTEM_OFF for preloading r0 (or x0)
 293                  * with PSCI return value INTERNAL_FAILURE.
 294                  */
 295                 val = PSCI_RET_INTERNAL_FAILURE;
 296                 ret = 0;
 297                 break;
 298         default:
 299                 val = PSCI_RET_NOT_SUPPORTED;
 300                 break;
 301         }
 302
 303 out:
 304         smccc_set_retval(vcpu, val, 0, 0, 0);
 305         return ret;
 306 }
 307
 308 static int kvm_psci_1_0_call(struct kvm_vcpu *vcpu)
 309 {
 310         u32 psci_fn = smccc_get_function(vcpu);
 311         u32 feature;
 312         unsigned long val;
 313         int ret = 1;
 314
 315         switch(psci_fn) {
 316         case PSCI_0_2_FN_PSCI_VERSION:
 317                 val = KVM_ARM_PSCI_1_0;
 318                 break;
 319         case PSCI_1_0_FN_PSCI_FEATURES:
 320                 feature = smccc_get_arg1(vcpu);
 321                 val = kvm_psci_check_allowed_function(vcpu, feature);
 322                 if (val)
 323                         break;
 324
 325                 switch(feature) {
 326                 case PSCI_0_2_FN_PSCI_VERSION:
 327                 case PSCI_0_2_FN_CPU_SUSPEND:
 328                 case PSCI_0_2_FN64_CPU_SUSPEND:
 329                 case PSCI_0_2_FN_CPU_OFF:
 330                 case PSCI_0_2_FN_CPU_ON:
 331                 case PSCI_0_2_FN64_CPU_ON:
 332                 case PSCI_0_2_FN_AFFINITY_INFO:
 333                 case PSCI_0_2_FN64_AFFINITY_INFO:
 334                 case PSCI_0_2_FN_MIGRATE_INFO_TYPE:
 335                 case PSCI_0_2_FN_SYSTEM_OFF:
 336                 case PSCI_0_2_FN_SYSTEM_RESET:
 337                 case PSCI_1_0_FN_PSCI_FEATURES:
 338                 case ARM_SMCCC_VERSION_FUNC_ID:
 339                         val = 0;
 340                         break;
 341                 default:
 342                         val = PSCI_RET_NOT_SUPPORTED;
 343                         break;
 344                 }
 345                 break;
 346         default:
 347                 return kvm_psci_0_2_call(vcpu);
 348         }
 349
 350         smccc_set_retval(vcpu, val, 0, 0, 0);
 351         return ret;
 352 }
 353
 354 static int kvm_psci_0_1_call(struct kvm_vcpu *vcpu)
 355 {
 356         struct kvm *kvm = vcpu->kvm;
 357         u32 psci_fn = smccc_get_function(vcpu);
 358         unsigned long val;
 359
 360         switch (psci_fn) {
 361         case KVM_PSCI_FN_CPU_OFF:
 362                 kvm_psci_vcpu_off(vcpu);
 363                 val = PSCI_RET_SUCCESS;
 364                 break;
 365         case KVM_PSCI_FN_CPU_ON:
 366                 mutex_lock(&kvm->lock);
 367                 val = kvm_psci_vcpu_on(vcpu);
 368                 mutex_unlock(&kvm->lock);
 369                 break;
 370         default:
 371                 val = PSCI_RET_NOT_SUPPORTED;
 372                 break;
 373         }
 374
 375         smccc_set_retval(vcpu, val, 0, 0, 0);
 376         return 1;
 377 }
 378
 379 /**
 380  * kvm_psci_call - handle PSCI call if r0 value is in range
 381  * @vcpu: Pointer to the VCPU struct
 382  *
 383  * Handle PSCI calls from guests through traps from HVC instructions.
 384  * The calling convention is similar to SMC calls to the secure world
 385  * where the function number is placed in r0.
 386  *
 387  * This function returns: > 0 (success), 0 (success but exit to user
 388  * space), and < 0 (errors)
 389  *
 390  * Errors:
 391  * -EINVAL: Unrecognized PSCI function
 392  */
 393 int kvm_psci_call(struct kvm_vcpu *vcpu)
 394 {
 395         switch (kvm_psci_version(vcpu, vcpu->kvm)) {
 396         case KVM_ARM_PSCI_1_0:
 397                 return kvm_psci_1_0_call(vcpu);
 398         case KVM_ARM_PSCI_0_2:
 399                 return kvm_psci_0_2_call(vcpu);
 400         case KVM_ARM_PSCI_0_1:
 401                 return kvm_psci_0_1_call(vcpu);
 402         default:
 403                 return -EINVAL;
 404         };
 405 }
 406
 407 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
 408 {
 409         return 4;               /* PSCI version and three workaround registers */
 410 }
 411
 412 int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
 413 {
 414         if (put_user(KVM_REG_ARM_PSCI_VERSION, uindices++))
 415                 return -EFAULT;
 416
 417         if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1, uindices++))
 418                 return -EFAULT;
 419
 420         if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2, uindices++))
 421                 return -EFAULT;
 422
 423         if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3, uindices++))
 424                 return -EFAULT;
 425
 426         return 0;
 427 }
 428
 429 #define KVM_REG_FEATURE_LEVEL_WIDTH     4
 430 #define KVM_REG_FEATURE_LEVEL_MASK      (BIT(KVM_REG_FEATURE_LEVEL_WIDTH) - 1)
 431
 432 /*
 433  * Convert the workaround level into an easy-to-compare number, where higher
 434  * values mean better protection.
 435  */
 436 static int get_kernel_wa_level(u64 regid)
 437 {
 438         switch (regid) {
 439         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
 440                 switch (arm64_get_spectre_v2_state()) {
 441                 case SPECTRE_VULNERABLE:
 442                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
 443                 case SPECTRE_MITIGATED:
 444                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL;
 445                 case SPECTRE_UNAFFECTED:
 446                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED;
 447                 }
 448                 return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
 449         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
 450                 switch (arm64_get_spectre_v4_state()) {
 451                 case SPECTRE_MITIGATED:
 452                         /*
 453                          * As for the hypercall discovery, we pretend we
 454                          * don't have any FW mitigation if SSBS is there at
 455                          * all times.
 456                          */
 457                         if (cpus_have_final_cap(ARM64_SSBS))
 458                                 return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
 459                         fallthrough;
 460                 case SPECTRE_UNAFFECTED:
 461                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED;
 462                 case SPECTRE_VULNERABLE:
 463                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
 464                 }
 465                 break;
 466         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
 467                 switch (arm64_get_spectre_bhb_state()) {
 468                 case SPECTRE_VULNERABLE:
 469                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_AVAIL;
 470                 case SPECTRE_MITIGATED:
 471                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_AVAIL;
 472                 case SPECTRE_UNAFFECTED:
 473                         return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_REQUIRED;
 474                 }
 475                 return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3_NOT_AVAIL;
 476         }
 477
 478         return -EINVAL;
 479 }
 480
 481 int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 482 {
 483         void __user *uaddr = (void __user *)(long)reg->addr;
 484         u64 val;
 485
 486         switch (reg->id) {
 487         case KVM_REG_ARM_PSCI_VERSION:
 488                 val = kvm_psci_version(vcpu, vcpu->kvm);
 489                 break;
 490         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
 491         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
 492         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
 493                 val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
 494                 break;
 495         default:
 496                 return -ENOENT;
 497         }
 498
 499         if (copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)))
 500                 return -EFAULT;
 501
 502         return 0;
 503 }
 504
 505 int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 506 {
 507         void __user *uaddr = (void __user *)(long)reg->addr;
 508         u64 val;
 509         int wa_level;
 510
 511         if (copy_from_user(&val, uaddr, KVM_REG_SIZE(reg->id)))
 512                 return -EFAULT;
 513
 514         switch (reg->id) {
 515         case KVM_REG_ARM_PSCI_VERSION:
 516         {
 517                 bool wants_02;
 518
 519                 wants_02 = test_bit(KVM_ARM_VCPU_PSCI_0_2, vcpu->arch.features);
 520
 521                 switch (val) {
 522                 case KVM_ARM_PSCI_0_1:
 523                         if (wants_02)
 524                                 return -EINVAL;
 525                         vcpu->kvm->arch.psci_version = val;
 526                         return 0;
 527                 case KVM_ARM_PSCI_0_2:
 528                 case KVM_ARM_PSCI_1_0:
 529                         if (!wants_02)
 530                                 return -EINVAL;
 531                         vcpu->kvm->arch.psci_version = val;
 532                         return 0;
 533                 }
 534                 break;
 535         }
 536
 537         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
 538         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
 539                 if (val & ~KVM_REG_FEATURE_LEVEL_MASK)
 540                         return -EINVAL;
 541
 542                 if (get_kernel_wa_level(reg->id) < val)
 543                         return -EINVAL;
 544
 545                 return 0;
 546
 547         case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
 548                 if (val & ~(KVM_REG_FEATURE_LEVEL_MASK |
 549                             KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED))
 550                         return -EINVAL;
 551
 552                 /* The enabled bit must not be set unless the level is AVAIL. */
 553                 if ((val & KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED) &&
 554                     (val & KVM_REG_FEATURE_LEVEL_MASK) != KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL)
 555                         return -EINVAL;
 556
 557                 /*
 558                  * Map all the possible incoming states to the only two we
 559                  * really want to deal with.
 560                  */
 561                 switch (val & KVM_REG_FEATURE_LEVEL_MASK) {
 562                 case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL:
 563                 case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN:
 564                         wa_level = KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
 565                         break;
 566                 case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL:
 567                 case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED:
 568                         wa_level = KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED;
 569                         break;
 570                 default:
 571                         return -EINVAL;
 572                 }
 573
 574                 /*
 575                  * We can deal with NOT_AVAIL on NOT_REQUIRED, but not the
 576                  * other way around.
 577                  */
 578                 if (get_kernel_wa_level(reg->id) < wa_level)
 579                         return -EINVAL;
 580
 581                 return 0;
 582         default:
 583                 return -ENOENT;
 584         }
 585
 586         return -EINVAL;
 587 }