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/sev.h>
  17 #include <asm/hypervisor.h>
  18 #include <asm/hyperv-tlfs.h>
  19 #include <asm/mshyperv.h>
  20 #include <asm/idtentry.h>
  21 #include <linux/kexec.h>
  22 #include <linux/version.h>
  23 #include <linux/vmalloc.h>
  24 #include <linux/mm.h>
  25 #include <linux/hyperv.h>
  26 #include <linux/slab.h>
  27 #include <linux/kernel.h>
  28 #include <linux/cpuhotplug.h>
  29 #include <linux/syscore_ops.h>
  30 #include <clocksource/hyperv_timer.h>
  31 #include <linux/highmem.h>
  32 #include <linux/swiotlb.h>
  33
  34 int hyperv_init_cpuhp;
  35 u64 hv_current_partition_id = ~0ull;
  36 EXPORT_SYMBOL_GPL(hv_current_partition_id);
  37
  38 void *hv_hypercall_pg;
  39 EXPORT_SYMBOL_GPL(hv_hypercall_pg);
  40
  41 union hv_ghcb * __percpu *hv_ghcb_pg;
  42
  43 /* Storage to save the hypercall page temporarily for hibernation */
  44 static void *hv_hypercall_pg_saved;
  45
  46 struct hv_vp_assist_page **hv_vp_assist_page;
  47 EXPORT_SYMBOL_GPL(hv_vp_assist_page);
  48
  49 static int hyperv_init_ghcb(void)
  50 {
  51         u64 ghcb_gpa;
  52         void *ghcb_va;
  53         void **ghcb_base;
  54
  55         if (!hv_isolation_type_snp())
  56                 return 0;
  57
  58         if (!hv_ghcb_pg)
  59                 return -EINVAL;
  60
  61         /*
  62          * GHCB page is allocated by paravisor. The address
  63          * returned by MSR_AMD64_SEV_ES_GHCB is above shared
  64          * memory boundary and map it here.
  65          */
  66         rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
  67         ghcb_va = memremap(ghcb_gpa, HV_HYP_PAGE_SIZE, MEMREMAP_WB);
  68         if (!ghcb_va)
  69                 return -ENOMEM;
  70
  71         ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
  72         *ghcb_base = ghcb_va;
  73
  74         return 0;
  75 }
  76
  77 static int hv_cpu_init(unsigned int cpu)
  78 {
  79         union hv_vp_assist_msr_contents msr = { 0 };
  80         struct hv_vp_assist_page **hvp = &hv_vp_assist_page[cpu];
  81         int ret;
  82
  83         ret = hv_common_cpu_init(cpu);
  84         if (ret)
  85                 return ret;
  86
  87         if (!hv_vp_assist_page)
  88                 return 0;
  89
  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 << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT,
  97                                 PAGE_SIZE, MEMREMAP_WB);
  98         } else {
  99                 /*
 100                  * The VP assist page is an "overlay" page (see Hyper-V TLFS's
 101                  * Section 5.2.1 "GPA Overlay Pages"). Here it must be zeroed
 102                  * out to make sure we always write the EOI MSR in
 103                  * hv_apic_eoi_write() *after* the EOI optimization is disabled
 104                  * in hv_cpu_die(), otherwise a CPU may not be stopped in the
 105                  * case of CPU offlining and the VM will hang.
 106                  */
 107                 if (!*hvp)
 108                         *hvp = __vmalloc(PAGE_SIZE, GFP_KERNEL | __GFP_ZERO);
 109                 if (*hvp)
 110                         msr.pfn = vmalloc_to_pfn(*hvp);
 111
 112         }
 113         if (!WARN_ON(!(*hvp))) {
 114                 msr.enable = 1;
 115                 wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 116         }
 117
 118         return hyperv_init_ghcb();
 119 }
 120
 121 static void (*hv_reenlightenment_cb)(void);
 122
 123 static void hv_reenlightenment_notify(struct work_struct *dummy)
 124 {
 125         struct hv_tsc_emulation_status emu_status;
 126
 127         rdmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 128
 129         /* Don't issue the callback if TSC accesses are not emulated */
 130         if (hv_reenlightenment_cb && emu_status.inprogress)
 131                 hv_reenlightenment_cb();
 132 }
 133 static DECLARE_DELAYED_WORK(hv_reenlightenment_work, hv_reenlightenment_notify);
 134
 135 void hyperv_stop_tsc_emulation(void)
 136 {
 137         u64 freq;
 138         struct hv_tsc_emulation_status emu_status;
 139
 140         rdmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 141         emu_status.inprogress = 0;
 142         wrmsrl(HV_X64_MSR_TSC_EMULATION_STATUS, *(u64 *)&emu_status);
 143
 144         rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
 145         tsc_khz = div64_u64(freq, 1000);
 146 }
 147 EXPORT_SYMBOL_GPL(hyperv_stop_tsc_emulation);
 148
 149 static inline bool hv_reenlightenment_available(void)
 150 {
 151         /*
 152          * Check for required features and privileges to make TSC frequency
 153          * change notifications work.
 154          */
 155         return ms_hyperv.features & HV_ACCESS_FREQUENCY_MSRS &&
 156                 ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE &&
 157                 ms_hyperv.features & HV_ACCESS_REENLIGHTENMENT;
 158 }
 159
 160 DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_reenlightenment)
 161 {
 162         ack_APIC_irq();
 163         inc_irq_stat(irq_hv_reenlightenment_count);
 164         schedule_delayed_work(&hv_reenlightenment_work, HZ/10);
 165 }
 166
 167 void set_hv_tscchange_cb(void (*cb)(void))
 168 {
 169         struct hv_reenlightenment_control re_ctrl = {
 170                 .vector = HYPERV_REENLIGHTENMENT_VECTOR,
 171                 .enabled = 1,
 172         };
 173         struct hv_tsc_emulation_control emu_ctrl = {.enabled = 1};
 174
 175         if (!hv_reenlightenment_available()) {
 176                 pr_warn("Hyper-V: reenlightenment support is unavailable\n");
 177                 return;
 178         }
 179
 180         if (!hv_vp_index)
 181                 return;
 182
 183         hv_reenlightenment_cb = cb;
 184
 185         /* Make sure callback is registered before we write to MSRs */
 186         wmb();
 187
 188         re_ctrl.target_vp = hv_vp_index[get_cpu()];
 189
 190         wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 191         wrmsrl(HV_X64_MSR_TSC_EMULATION_CONTROL, *((u64 *)&emu_ctrl));
 192
 193         put_cpu();
 194 }
 195 EXPORT_SYMBOL_GPL(set_hv_tscchange_cb);
 196
 197 void clear_hv_tscchange_cb(void)
 198 {
 199         struct hv_reenlightenment_control re_ctrl;
 200
 201         if (!hv_reenlightenment_available())
 202                 return;
 203
 204         rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
 205         re_ctrl.enabled = 0;
 206         wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *(u64 *)&re_ctrl);
 207
 208         hv_reenlightenment_cb = NULL;
 209 }
 210 EXPORT_SYMBOL_GPL(clear_hv_tscchange_cb);
 211
 212 static int hv_cpu_die(unsigned int cpu)
 213 {
 214         struct hv_reenlightenment_control re_ctrl;
 215         unsigned int new_cpu;
 216         void **ghcb_va;
 217
 218         if (hv_ghcb_pg) {
 219                 ghcb_va = (void **)this_cpu_ptr(hv_ghcb_pg);
 220                 if (*ghcb_va)
 221                         memunmap(*ghcb_va);
 222                 *ghcb_va = NULL;
 223         }
 224
 225         hv_common_cpu_die(cpu);
 226
 227         if (hv_vp_assist_page && hv_vp_assist_page[cpu]) {
 228                 union hv_vp_assist_msr_contents msr = { 0 };
 229                 if (hv_root_partition) {
 230                         /*
 231                          * For root partition the VP assist page is mapped to
 232                          * hypervisor provided page, and thus we unmap the
 233                          * page here and nullify it, so that in future we have
 234                          * correct page address mapped in hv_cpu_init.
 235                          */
 236                         memunmap(hv_vp_assist_page[cpu]);
 237                         hv_vp_assist_page[cpu] = NULL;
 238                         rdmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 239                         msr.enable = 0;
 240                 }
 241                 wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
 242         }
 243
 244         if (hv_reenlightenment_cb == NULL)
 245                 return 0;
 246
 247         rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 248         if (re_ctrl.target_vp == hv_vp_index[cpu]) {
 249                 /*
 250                  * Reassign reenlightenment notifications to some other online
 251                  * CPU or just disable the feature if there are no online CPUs
 252                  * left (happens on hibernation).
 253                  */
 254                 new_cpu = cpumask_any_but(cpu_online_mask, cpu);
 255
 256                 if (new_cpu < nr_cpu_ids)
 257                         re_ctrl.target_vp = hv_vp_index[new_cpu];
 258                 else
 259                         re_ctrl.enabled = 0;
 260
 261                 wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
 262         }
 263
 264         return 0;
 265 }
 266
 267 static int __init hv_pci_init(void)
 268 {
 269         int gen2vm = efi_enabled(EFI_BOOT);
 270
 271         /*
 272          * For Generation-2 VM, we exit from pci_arch_init() by returning 0.
 273          * The purpose is to suppress the harmless warning:
 274          * "PCI: Fatal: No config space access function found"
 275          */
 276         if (gen2vm)
 277                 return 0;
 278
 279         /* For Generation-1 VM, we'll proceed in pci_arch_init().  */
 280         return 1;
 281 }
 282
 283 static int hv_suspend(void)
 284 {
 285         union hv_x64_msr_hypercall_contents hypercall_msr;
 286         int ret;
 287
 288         if (hv_root_partition)
 289                 return -EPERM;
 290
 291         /*
 292          * Reset the hypercall page as it is going to be invalidated
 293          * across hibernation. Setting hv_hypercall_pg to NULL ensures
 294          * that any subsequent hypercall operation fails safely instead of
 295          * crashing due to an access of an invalid page. The hypercall page
 296          * pointer is restored on resume.
 297          */
 298         hv_hypercall_pg_saved = hv_hypercall_pg;
 299         hv_hypercall_pg = NULL;
 300
 301         /* Disable the hypercall page in the hypervisor */
 302         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 303         hypercall_msr.enable = 0;
 304         wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 305
 306         ret = hv_cpu_die(0);
 307         return ret;
 308 }
 309
 310 static void hv_resume(void)
 311 {
 312         union hv_x64_msr_hypercall_contents hypercall_msr;
 313         int ret;
 314
 315         ret = hv_cpu_init(0);
 316         WARN_ON(ret);
 317
 318         /* Re-enable the hypercall page */
 319         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 320         hypercall_msr.enable = 1;
 321         hypercall_msr.guest_physical_address =
 322                 vmalloc_to_pfn(hv_hypercall_pg_saved);
 323         wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 324
 325         hv_hypercall_pg = hv_hypercall_pg_saved;
 326         hv_hypercall_pg_saved = NULL;
 327
 328         /*
 329          * Reenlightenment notifications are disabled by hv_cpu_die(0),
 330          * reenable them here if hv_reenlightenment_cb was previously set.
 331          */
 332         if (hv_reenlightenment_cb)
 333                 set_hv_tscchange_cb(hv_reenlightenment_cb);
 334 }
 335
 336 /* Note: when the ops are called, only CPU0 is online and IRQs are disabled. */
 337 static struct syscore_ops hv_syscore_ops = {
 338         .suspend        = hv_suspend,
 339         .resume         = hv_resume,
 340 };
 341
 342 static void (* __initdata old_setup_percpu_clockev)(void);
 343
 344 static void __init hv_stimer_setup_percpu_clockev(void)
 345 {
 346         /*
 347          * Ignore any errors in setting up stimer clockevents
 348          * as we can run with the LAPIC timer as a fallback.
 349          */
 350         (void)hv_stimer_alloc(false);
 351
 352         /*
 353          * Still register the LAPIC timer, because the direct-mode STIMER is
 354          * not supported by old versions of Hyper-V. This also allows users
 355          * to switch to LAPIC timer via /sys, if they want to.
 356          */
 357         if (old_setup_percpu_clockev)
 358                 old_setup_percpu_clockev();
 359 }
 360
 361 static void __init hv_get_partition_id(void)
 362 {
 363         struct hv_get_partition_id *output_page;
 364         u64 status;
 365         unsigned long flags;
 366
 367         local_irq_save(flags);
 368         output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
 369         status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
 370         if (!hv_result_success(status)) {
 371                 /* No point in proceeding if this failed */
 372                 pr_err("Failed to get partition ID: %lld\n", status);
 373                 BUG();
 374         }
 375         hv_current_partition_id = output_page->partition_id;
 376         local_irq_restore(flags);
 377 }
 378
 379 /*
 380  * This function is to be invoked early in the boot sequence after the
 381  * hypervisor has been detected.
 382  *
 383  * 1. Setup the hypercall page.
 384  * 2. Register Hyper-V specific clocksource.
 385  * 3. Setup Hyper-V specific APIC entry points.
 386  */
 387 void __init hyperv_init(void)
 388 {
 389         u64 guest_id;
 390         union hv_x64_msr_hypercall_contents hypercall_msr;
 391         int cpuhp;
 392
 393         if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 394                 return;
 395
 396         if (hv_common_init())
 397                 return;
 398
 399         hv_vp_assist_page = kcalloc(num_possible_cpus(),
 400                                     sizeof(*hv_vp_assist_page), GFP_KERNEL);
 401         if (!hv_vp_assist_page) {
 402                 ms_hyperv.hints &= ~HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;
 403                 goto common_free;
 404         }
 405
 406         if (hv_isolation_type_snp()) {
 407                 /* Negotiate GHCB Version. */
 408                 if (!hv_ghcb_negotiate_protocol())
 409                         hv_ghcb_terminate(SEV_TERM_SET_GEN,
 410                                           GHCB_SEV_ES_PROT_UNSUPPORTED);
 411
 412                 hv_ghcb_pg = alloc_percpu(union hv_ghcb *);
 413                 if (!hv_ghcb_pg)
 414                         goto free_vp_assist_page;
 415         }
 416
 417         cpuhp = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/hyperv_init:online",
 418                                   hv_cpu_init, hv_cpu_die);
 419         if (cpuhp < 0)
 420                 goto free_ghcb_page;
 421
 422         /*
 423          * Setup the hypercall page and enable hypercalls.
 424          * 1. Register the guest ID
 425          * 2. Enable the hypercall and register the hypercall page
 426          */
 427         guest_id = hv_generate_guest_id(LINUX_VERSION_CODE);
 428         wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
 429
 430         /* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
 431         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
 432
 433         hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,
 434                         VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
 435                         VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
 436                         __builtin_return_address(0));
 437         if (hv_hypercall_pg == NULL)
 438                 goto clean_guest_os_id;
 439
 440         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 441         hypercall_msr.enable = 1;
 442
 443         if (hv_root_partition) {
 444                 struct page *pg;
 445                 void *src;
 446
 447                 /*
 448                  * For the root partition, the hypervisor will set up its
 449                  * hypercall page. The hypervisor guarantees it will not show
 450                  * up in the root's address space. The root can't change the
 451                  * location of the hypercall page.
 452                  *
 453                  * Order is important here. We must enable the hypercall page
 454                  * so it is populated with code, then copy the code to an
 455                  * executable page.
 456                  */
 457                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 458
 459                 pg = vmalloc_to_page(hv_hypercall_pg);
 460                 src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE,
 461                                 MEMREMAP_WB);
 462                 BUG_ON(!src);
 463                 memcpy_to_page(pg, 0, src, HV_HYP_PAGE_SIZE);
 464                 memunmap(src);
 465         } else {
 466                 hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
 467                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 468         }
 469
 470         /*
 471          * hyperv_init() is called before LAPIC is initialized: see
 472          * apic_intr_mode_init() -> x86_platform.apic_post_init() and
 473          * apic_bsp_setup() -> setup_local_APIC(). The direct-mode STIMER
 474          * depends on LAPIC, so hv_stimer_alloc() should be called from
 475          * x86_init.timers.setup_percpu_clockev.
 476          */
 477         old_setup_percpu_clockev = x86_init.timers.setup_percpu_clockev;
 478         x86_init.timers.setup_percpu_clockev = hv_stimer_setup_percpu_clockev;
 479
 480         hv_apic_init();
 481
 482         x86_init.pci.arch_init = hv_pci_init;
 483
 484         register_syscore_ops(&hv_syscore_ops);
 485
 486         hyperv_init_cpuhp = cpuhp;
 487
 488         if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
 489                 hv_get_partition_id();
 490
 491         BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
 492
 493 #ifdef CONFIG_PCI_MSI
 494         /*
 495          * If we're running as root, we want to create our own PCI MSI domain.
 496          * We can't set this in hv_pci_init because that would be too late.
 497          */
 498         if (hv_root_partition)
 499                 x86_init.irqs.create_pci_msi_domain = hv_create_pci_msi_domain;
 500 #endif
 501
 502         /* Query the VMs extended capability once, so that it can be cached. */
 503         hv_query_ext_cap(0);
 504
 505 #ifdef CONFIG_SWIOTLB
 506         /*
 507          * Swiotlb bounce buffer needs to be mapped in extra address
 508          * space. Map function doesn't work in the early place and so
 509          * call swiotlb_update_mem_attributes() here.
 510          */
 511         if (hv_is_isolation_supported())
 512                 swiotlb_update_mem_attributes();
 513 #endif
 514
 515         return;
 516
 517 clean_guest_os_id:
 518         wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 519         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 520         cpuhp_remove_state(cpuhp);
 521 free_ghcb_page:
 522         free_percpu(hv_ghcb_pg);
 523 free_vp_assist_page:
 524         kfree(hv_vp_assist_page);
 525         hv_vp_assist_page = NULL;
 526 common_free:
 527         hv_common_free();
 528 }
 529
 530 /*
 531  * This routine is called before kexec/kdump, it does the required cleanup.
 532  */
 533 void hyperv_cleanup(void)
 534 {
 535         union hv_x64_msr_hypercall_contents hypercall_msr;
 536         union hv_reference_tsc_msr tsc_msr;
 537
 538         unregister_syscore_ops(&hv_syscore_ops);
 539
 540         /* Reset our OS id */
 541         wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 542         hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 543
 544         /*
 545          * Reset hypercall page reference before reset the page,
 546          * let hypercall operations fail safely rather than
 547          * panic the kernel for using invalid hypercall page
 548          */
 549         hv_hypercall_pg = NULL;
 550
 551         /* Reset the hypercall page */
 552         hypercall_msr.as_uint64 = hv_get_register(HV_X64_MSR_HYPERCALL);
 553         hypercall_msr.enable = 0;
 554         hv_set_register(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 555
 556         /* Reset the TSC page */
 557         tsc_msr.as_uint64 = hv_get_register(HV_X64_MSR_REFERENCE_TSC);
 558         tsc_msr.enable = 0;
 559         hv_set_register(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
 560 }
 561
 562 void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
 563 {
 564         static bool panic_reported;
 565         u64 guest_id;
 566
 567         if (in_die && !panic_on_oops)
 568                 return;
 569
 570         /*
 571          * We prefer to report panic on 'die' chain as we have proper
 572          * registers to report, but if we miss it (e.g. on BUG()) we need
 573          * to report it on 'panic'.
 574          */
 575         if (panic_reported)
 576                 return;
 577         panic_reported = true;
 578
 579         rdmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
 580
 581         wrmsrl(HV_X64_MSR_CRASH_P0, err);
 582         wrmsrl(HV_X64_MSR_CRASH_P1, guest_id);
 583         wrmsrl(HV_X64_MSR_CRASH_P2, regs->ip);
 584         wrmsrl(HV_X64_MSR_CRASH_P3, regs->ax);
 585         wrmsrl(HV_X64_MSR_CRASH_P4, regs->sp);
 586
 587         /*
 588          * Let Hyper-V know there is crash data available
 589          */
 590         wrmsrl(HV_X64_MSR_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
 591 }
 592 EXPORT_SYMBOL_GPL(hyperv_report_panic);
 593
 594 bool hv_is_hyperv_initialized(void)
 595 {
 596         union hv_x64_msr_hypercall_contents hypercall_msr;
 597
 598         /*
 599          * Ensure that we're really on Hyper-V, and not a KVM or Xen
 600          * emulation of Hyper-V
 601          */
 602         if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 603                 return false;
 604
 605         /*
 606          * Verify that earlier initialization succeeded by checking
 607          * that the hypercall page is setup
 608          */
 609         hypercall_msr.as_uint64 = 0;
 610         rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 611
 612         return hypercall_msr.enable;
 613 }
 614 EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);