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