arch/x86/hyperv/hv_init.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * X86 specific Hyper-V initialization code.
   4  *
   5  * Copyright (C) 2016, Microsoft, Inc.
   6  *
   7  * Author : K. Y. Srinivasan <kys@microsoft.com>
   8  */
   9
  10 #include <linux/efi.h>
  11 #include <linux/types.h>
  12 #include <linux/bitfield.h>
  13 #include <linux/io.h>
  14 #include <asm/apic.h>
  15 #include <asm/desc.h>
  16 #include <asm/hypervisor.h>
  17 #include <asm/hyperv-tlfs.h>
  18 #include <asm/mshyperv.h>
  19 #include <asm/idtentry.h>
  20 #include <linux/kexec.h>
  21 #include <linux/version.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/mm.h>
  24 #include <linux/hyperv.h>
  25 #include <linux/slab.h>
  26 #include <linux/kernel.h>
  27 #include <linux/cpuhotplug.h>
  28 #include <linux/syscore_ops.h>
  29 #include <clocksource/hyperv_timer.h>
  30 #include <linux/highmem.h>
  31 #include <linux/swiotlb.h>
  32
  33 int hyperv_init_cpuhp;
  34 u64 hv_current_partition_id = ~0ull;
  35 EXPORT_SYMBOL_GPL(hv_current_partition_id);
  36
  37 void *hv_hypercall_pg;
  38 EXPORT_SYMBOL_GPL(hv_hypercall_pg);
  39
  40 union hv_ghcb * __percpu *hv_ghcb_pg;
  41
  42 /* Storage to save the hypercall page temporarily for hibernation */
  43 static void *hv_hypercall_pg_saved;
  44
  45 struct hv_vp_assist_page **hv_vp_assist_page;
  46 EXPORT_SYMBOL_GPL(hv_vp_assist_page);
  47
  48 static int hyperv_init_ghcb(void)
  49 {
  50         u64 ghcb_gpa;
  51         void *ghcb_va;
  52         void **ghcb_base;
  53
  54         if (!hv_isolation_type_snp())
  55                 return 0;
  56
  57         if (!hv_ghcb_pg)
  58                 return -EINVAL;
  59
  60         /*
  61          * GHCB page is allocated by paravisor. The address
  62          * returned by MSR_AMD64_SEV_ES_GHCB is above shared
  63          * memory boundary and map it here.
  64          */
  65         rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
  66         ghcb_va = memremap(ghcb_gpa, HV_HYP_PAGE_SIZE, MEMREMAP_WB);
  67         if (!ghcb_va)
  68                 return -ENOMEM;
  69
  70         ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
  71         *ghcb_base = ghcb_va;
  72
  73         return 0;
  74 }
  75
  76 static int hv_cpu_init(unsigned int cpu)
  77 {
  78         union hv_vp_assist_msr_contents msr = { 0 };
  79         struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
  80         int ret;
  81
  82         ret = hv_common_cpu_init(cpu);
  83         if (ret)
  84                 return ret;
  85
  86         if (!hv_vp_assist_page)
  87                 return 0;
  88
  89         if (!*hvp) {
  90                 if (hv_root_partition) {
  91                         /*
  92                          * For root partition we get the hypervisor provided VP assist
  93                          * page, instead of allocating a new page.
  94                          */
  95                         rdmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
  96                         *hvp = memremap(msr.pfn <<
  97                                         HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT,
  98                                         PAGE_SIZE, MEMREMAP_WB);
  99                 } else {
 100                         /*
 101                          * The VP assist page is an "overlay" page (see Hyper-V TLFS's
 102                          * Section 5.2.1 "GPA Overlay Pages"). Here it must be zeroed
 103                          * out to make sure we always write the EOI MSR in
 104                          * hv_apic_eoi_write() *after* the EOI optimization is disabled
 105                          * in hv_cpu_die(), otherwise a CPU may not be stopped in the
 106                          * case of CPU offlining and the VM will hang.
 107                          */
 108                         *hvp = __vmalloc(PAGE_SIZE, GFP_KERNEL | __GFP_ZERO);
 109                         if (*hvp)
 110                                 msr.pfn = vmalloc_to_pfn(*hvp);
 111                 }
 112                 WARN_ON(!(*hvp));
 113                 if (*hvp) {
 114                         msr.enable = 1;
 115                         wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 116                 }
 117         }
 118
 119         return hyperv_init_ghcb();
 120 }
 121
 122 static void (*hv_reenlightenment_cb)(void);
 123
 124 static void hv_reenlightenment_notify(struct work_struct *dummy)
 125 {
 126         struct hv_tsc_emulation_status emu_status;
 127
 128         rdmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 129
 130         /* Don't issue the callback if TSC accesses are not emulated */
 131         if (hv_reenlightenment_cb && emu_status.inprogress)
 132                 hv_reenlightenment_cb();
 133 }
 134 static DECLARE_DELAYED_WORK(hv_reenlightenment_work, hv_reenlightenment_notify);
 135
 136 void hyperv_stop_tsc_emulation(void)
 137 {
 138         u64 freq;
 139         struct hv_tsc_emulation_status emu_status;
 140
 141         rdmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 142         emu_status.inprogress = 0;
 143         wrmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 144
 145         rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
 146         tsc_khz = div64_u64(freq, 1000);
 147 }
 148 EXPORT_SYMBOL_GPL(hyperv_stop_tsc_emulation);
 149
 150 static inline bool hv_reenlightenment_available(void)
 151 {
 152         /*
 153          * Check for required features and privileges to make TSC frequency
 154          * change notifications work.
 155          */
 156         return ms_hyperv.features & HV_ACCESS_FREQUENCY_MSRS &&
 157                 ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE &&
 158                 ms_hyperv.features & HV_ACCESS_REENLIGHTENMENT;
 159 }
 160
 161 DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_reenlightenment)
 162 {
 163         ack_APIC_irq();
 164         inc_irq_stat(irq_hv_reenlightenment_count);
 165         schedule_delayed_work(&hv_reenlightenment_work, HZ/10);
 166 }
 167
 168 void set_hv_tscchange_cb(void (*cb)(void))
 169 {
 170         struct hv_reenlightenment_control re_ctrl = {
 171                 .vector = HYPERV_REENLIGHTENMENT_VECTOR,
 172                 .enabled = 1,
 173         };
 174         struct hv_tsc_emulation_control emu_ctrl = {.enabled = 1};
 175
 176         if (!hv_reenlightenment_available()) {
 177                 pr_warn("Hyper-V: reenlightenment support is unavailable\n");
 178                 return;
 179         }
 180
 181         if (!hv_vp_index)
 182                 return;
 183
 184         hv_reenlightenment_cb = cb;
 185
 186         /* Make sure callback is registered before we write to MSRs */
 187         wmb();
 188
 189         re_ctrl.target_vp = hv_vp_index[get_cpu()];
 190
 191         wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 192         wrmsrl(HV_X64_MSR_TSC_EMULATION_CONTROL, *((u64 *)&emu_ctrl));
 193
 194         put_cpu();
 195 }
 196 EXPORT_SYMBOL_GPL(set_hv_tscchange_cb);
 197
 198 void clear_hv_tscchange_cb(void)
 199 {
 200         struct hv_reenlightenment_control re_ctrl;
 201
 202         if (!hv_reenlightenment_available())
 203                 return;
 204
 205         rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
 206         re_ctrl.enabled = 0;
 207         wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
 208
 209         hv_reenlightenment_cb = NULL;
 210 }
 211 EXPORT_SYMBOL_GPL(clear_hv_tscchange_cb);
 212
 213 static int hv_cpu_die(unsigned int cpu)
 214 {
 215         struct hv_reenlightenment_control re_ctrl;
 216         unsigned int new_cpu;
 217         void **ghcb_va;
 218
 219         if (hv_ghcb_pg) {
 220                 ghcb_va = (void **)this_cpu_ptr(hv_ghcb_pg);
 221                 if (*ghcb_va)
 222                         memunmap(*ghcb_va);
 223                 *ghcb_va = NULL;
 224         }
 225
 226         hv_common_cpu_die(cpu);
 227
 228         if (hv_vp_assist_page && hv_vp_assist_page[cpu]) {
 229                 union hv_vp_assist_msr_contents msr = { 0 };
 230                 if (hv_root_partition) {
 231                         /*
 232                          * For root partition the VP assist page is mapped to
 233                          * hypervisor provided page, and thus we unmap the
 234                          * page here and nullify it, so that in future we have
 235                          * correct page address mapped in hv_cpu_init.
 236                          */
 237                         memunmap(hv_vp_assist_page[cpu]);
 238                         hv_vp_assist_page[cpu] = NULL;
 239                         rdmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 240                         msr.enable = 0;
 241                 }
 242                 wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 243         }
 244
 245         if (hv_reenlightenment_cb == NULL)
 246                 return 0;
 247
 248         rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 249         if (re_ctrl.target_vp == hv_vp_index[cpu]) {
 250                 /*
 251                  * Reassign reenlightenment notifications to some other online
 252                  * CPU or just disable the feature if there are no online CPUs
 253                  * left (happens on hibernation).
 254                  */
 255                 new_cpu = cpumask_any_but(cpu_online_mask, cpu);
 256
 257                 if (new_cpu < nr_cpu_ids)
 258                         re_ctrl.target_vp = hv_vp_index[new_cpu];
 259                 else
 260                         re_ctrl.enabled = 0;
 261
 262                 wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 263         }
 264
 265         return 0;
 266 }
 267
 268 static int __init hv_pci_init(void)
 269 {
 270         int gen2vm = efi_enabled(EFI_BOOT);
 271
 272         /*
 273          * For Generation-2 VM, we exit from pci_arch_init() by returning 0.
 274          * The purpose is to suppress the harmless warning:
 275          * "PCI: Fatal: No config space access function found"
 276          */
 277         if (gen2vm)
 278                 return 0;
 279
 280         /* For Generation-1 VM, we'll proceed in pci_arch_init().  */
 281         return 1;
 282 }
 283
 284 static int hv_suspend(void)
 285 {
 286         union hv_x64_msr_hypercall_contents hypercall_msr;
 287         int ret;
 288
 289         if (hv_root_partition)
 290                 return -EPERM;
 291
 292         /*
 293          * Reset the hypercall page as it is going to be invalidated
 294          * across hibernation. Setting hv_hypercall_pg to NULL ensures
 295          * that any subsequent hypercall operation fails safely instead of
 296          * crashing due to an access of an invalid page. The hypercall page
 297          * pointer is restored on resume.
 298          */
 299         hv_hypercall_pg_saved = hv_hypercall_pg;
 300         hv_hypercall_pg = NULL;
 301
 302         /* Disable the hypercall page in the hypervisor */
 303         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 304         hypercall_msr.enable = 0;
 305         wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 306
 307         ret = hv_cpu_die(0);
 308         return ret;
 309 }
 310
 311 static void hv_resume(void)
 312 {
 313         union hv_x64_msr_hypercall_contents hypercall_msr;
 314         int ret;
 315
 316         ret = hv_cpu_init(0);
 317         WARN_ON(ret);
 318
 319         /* Re-enable the hypercall page */
 320         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 321         hypercall_msr.enable = 1;
 322         hypercall_msr.guest_physical_address =
 323                 vmalloc_to_pfn(hv_hypercall_pg_saved);
 324         wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 325
 326         hv_hypercall_pg = hv_hypercall_pg_saved;
 327         hv_hypercall_pg_saved = NULL;
 328
 329         /*
 330          * Reenlightenment notifications are disabled by hv_cpu_die(0),
 331          * reenable them here if hv_reenlightenment_cb was previously set.
 332          */
 333         if (hv_reenlightenment_cb)
 334                 set_hv_tscchange_cb(hv_reenlightenment_cb);
 335 }
 336
 337 /* Note: when the ops are called, only CPU0 is online and IRQs are disabled. */
 338 static struct syscore_ops hv_syscore_ops = {
 339         .suspend        = hv_suspend,
 340         .resume         = hv_resume,
 341 };
 342
 343 static void (* __initdata old_setup_percpu_clockev)(void);
 344
 345 static void __init hv_stimer_setup_percpu_clockev(void)
 346 {
 347         /*
 348          * Ignore any errors in setting up stimer clockevents
 349          * as we can run with the LAPIC timer as a fallback.
 350          */
 351         (void)hv_stimer_alloc(false);
 352
 353         /*
 354          * Still register the LAPIC timer, because the direct-mode STIMER is
 355          * not supported by old versions of Hyper-V. This also allows users
 356          * to switch to LAPIC timer via /sys, if they want to.
 357          */
 358         if (old_setup_percpu_clockev)
 359                 old_setup_percpu_clockev();
 360 }
 361
 362 static void __init hv_get_partition_id(void)
 363 {
 364         struct hv_get_partition_id *output_page;
 365         u64 status;
 366         unsigned long flags;
 367
 368         local_irq_save(flags);
 369         output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
 370         status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
 371         if (!hv_result_success(status)) {
 372                 /* No point in proceeding if this failed */
 373                 pr_err("Failed to get partition ID: %lld\n", status);
 374                 BUG();
 375         }
 376         hv_current_partition_id = output_page->partition_id;
 377         local_irq_restore(flags);
 378 }
 379
 380 /*
 381  * This function is to be invoked early in the boot sequence after the
 382  * hypervisor has been detected.
 383  *
 384  * 1. Setup the hypercall page.
 385  * 2. Register Hyper-V specific clocksource.
 386  * 3. Setup Hyper-V specific APIC entry points.
 387  */
 388 void __init hyperv_init(void)
 389 {
 390         u64 guest_id;
 391         union hv_x64_msr_hypercall_contents hypercall_msr;
 392         int cpuhp;
 393
 394         if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 395                 return;
 396
 397         if (hv_common_init())
 398                 return;
 399
 400         hv_vp_assist_page = kcalloc(num_possible_cpus(),
 401                                     sizeof(*hv_vp_assist_page), GFP_KERNEL);
 402         if (!hv_vp_assist_page) {
 403                 ms_hyperv.hints &= ~HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;
 404                 goto common_free;
 405         }
 406
 407         if (hv_isolation_type_snp()) {
 408                 hv_ghcb_pg = alloc_percpu(union hv_ghcb *);
 409                 if (!hv_ghcb_pg)
 410                         goto free_vp_assist_page;
 411         }
 412
 413         cpuhp = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/hyperv_init:online",
 414                                   hv_cpu_init, hv_cpu_die);
 415         if (cpuhp < 0)
 416                 goto free_ghcb_page;
 417
 418         /*
 419          * Setup the hypercall page and enable hypercalls.
 420          * 1. Register the guest ID
 421          * 2. Enable the hypercall and register the hypercall page
 422          */
 423         guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
 424         wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
 425
 426         /* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
 427         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
 428
 429         hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,
 430                         VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
 431                         VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
 432                         __builtin_return_address(0));
 433         if (hv_hypercall_pg == NULL)
 434                 goto clean_guest_os_id;
 435
 436         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 437         hypercall_msr.enable = 1;
 438
 439         if (hv_root_partition) {
 440                 struct page *pg;
 441                 void *src, *dst;
 442
 443                 /*
 444                  * For the root partition, the hypervisor will set up its
 445                  * hypercall page. The hypervisor guarantees it will not show
 446                  * up in the root's address space. The root can't change the
 447                  * location of the hypercall page.
 448                  *
 449                  * Order is important here. We must enable the hypercall page
 450                  * so it is populated with code, then copy the code to an
 451                  * executable page.
 452                  */
 453                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 454
 455                 pg = vmalloc_to_page(hv_hypercall_pg);
 456                 dst = kmap(pg);
 457                 src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE,
 458                                 MEMREMAP_WB);
 459                 BUG_ON(!(src && dst));
 460                 memcpy(dst, src, HV_HYP_PAGE_SIZE);
 461                 memunmap(src);
 462                 kunmap(pg);
 463         } else {
 464                 hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
 465                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 466         }
 467
 468         /*
 469          * hyperv_init() is called before LAPIC is initialized: see
 470          * apic_intr_mode_init() -> x86_platform.apic_post_init() and
 471          * apic_bsp_setup() -> setup_local_APIC(). The direct-mode STIMER
 472          * depends on LAPIC, so hv_stimer_alloc() should be called from
 473          * x86_init.timers.setup_percpu_clockev.
 474          */
 475         old_setup_percpu_clockev = x86_init.timers.setup_percpu_clockev;
 476         x86_init.timers.setup_percpu_clockev = hv_stimer_setup_percpu_clockev;
 477
 478         hv_apic_init();
 479
 480         x86_init.pci.arch_init = hv_pci_init;
 481
 482         register_syscore_ops(&hv_syscore_ops);
 483
 484         hyperv_init_cpuhp = cpuhp;
 485
 486         if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
 487                 hv_get_partition_id();
 488
 489         BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
 490
 491 #ifdef CONFIG_PCI_MSI
 492         /*
 493          * If we're running as root, we want to create our own PCI MSI domain.
 494          * We can't set this in hv_pci_init because that would be too late.
 495          */
 496         if (hv_root_partition)
 497                 x86_init.irqs.create_pci_msi_domain = hv_create_pci_msi_domain;
 498 #endif
 499
 500         /* Query the VMs extended capability once, so that it can be cached. */
 501         hv_query_ext_cap(0);
 502
 503 #ifdef CONFIG_SWIOTLB
 504         /*
 505          * Swiotlb bounce buffer needs to be mapped in extra address
 506          * space. Map function doesn't work in the early place and so
 507          * call swiotlb_update_mem_attributes() here.
 508          */
 509         if (hv_is_isolation_supported())
 510                 swiotlb_update_mem_attributes();
 511 #endif
 512
 513         return;
 514
 515 clean_guest_os_id:
 516         wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 517         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 518         cpuhp_remove_state(cpuhp);
 519 free_ghcb_page:
 520         free_percpu(hv_ghcb_pg);
 521 free_vp_assist_page:
 522         kfree(hv_vp_assist_page);
 523         hv_vp_assist_page = NULL;
 524 common_free:
 525         hv_common_free();
 526 }
 527
 528 /*
 529  * This routine is called before kexec/kdump, it does the required cleanup.
 530  */
 531 void hyperv_cleanup(void)
 532 {
 533         union hv_x64_msr_hypercall_contents hypercall_msr;
 534
 535         unregister_syscore_ops(&hv_syscore_ops);
 536
 537         /* Reset our OS id */
 538         wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 539         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 540
 541         /*
 542          * Reset hypercall page reference before reset the page,
 543          * let hypercall operations fail safely rather than
 544          * panic the kernel for using invalid hypercall page
 545          */
 546         hv_hypercall_pg = NULL;
 547
 548         /* Reset the hypercall page */
 549         hypercall_msr.as_uint64 = 0;
 550         wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 551
 552         /* Reset the TSC page */
 553         hypercall_msr.as_uint64 = 0;
 554         wrmsrl(HV_X64_MSR_REFERENCE_TSC, hypercall_msr.as_uint64);
 555 }
 556
 557 void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
 558 {
 559         static bool panic_reported;
 560         u64 guest_id;
 561
 562         if (in_die && !panic_on_oops)
 563                 return;
 564
 565         /*
 566          * We prefer to report panic on 'die' chain as we have proper
 567          * registers to report, but if we miss it (e.g. on BUG()) we need
 568          * to report it on 'panic'.
 569          */
 570         if (panic_reported)
 571                 return;
 572         panic_reported = true;
 573
 574         rdmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
 575
 576         wrmsrl(HV_X64_MSR_CRASH_P0, err);
 577         wrmsrl(HV_X64_MSR_CRASH_P1, guest_id);
 578         wrmsrl(HV_X64_MSR_CRASH_P2, regs->ip);
 579         wrmsrl(HV_X64_MSR_CRASH_P3, regs->ax);
 580         wrmsrl(HV_X64_MSR_CRASH_P4, regs->sp);
 581
 582         /*
 583          * Let Hyper-V know there is crash data available
 584          */
 585         wrmsrl(HV_X64_MSR_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
 586 }
 587 EXPORT_SYMBOL_GPL(hyperv_report_panic);
 588
 589 bool hv_is_hyperv_initialized(void)
 590 {
 591         union hv_x64_msr_hypercall_contents hypercall_msr;
 592
 593         /*
 594          * Ensure that we're really on Hyper-V, and not a KVM or Xen
 595          * emulation of Hyper-V
 596          */
 597         if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 598                 return false;
 599
 600         /*
 601          * Verify that earlier initialization succeeded by checking
 602          * that the hypercall page is setup
 603          */
 604         hypercall_msr.as_uint64 = 0;
 605         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 606
 607         return hypercall_msr.enable;
 608 }
 609 EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);