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hypercalls.txt

hypercalls.txt 2.2 KB
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  1. Linux KVM Hypercall:
    2. 

  2. ===================
    3. 

  3. X86:
    4. 

  4.  KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
    5. 

  5.  instruction. The hypervisor can replace it with instructions that are
    6. 

  6.  guaranteed to be supported.
    7. 

  7. 

  8.  Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
    9. 

  9.  The hypercall number should be placed in rax and the return value will be
    10. 

  10.  placed in rax.  No other registers will be clobbered unless explicitly stated
    11. 

  11.  by the particular hypercall.
    12. 

  12. 

  13. S390:
    14. 

  14.   R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
    15. 

  15.   number. The return value is written to R2.
    16. 

  16. 

  17.   S390 uses diagnose instruction as hypercall (0x500) along with hypercall
    18. 

  18.   number in R1.
    19. 

  19. 

  20.  PowerPC:
    21. 

  21.   It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
    22. 

  22.   Return value is placed in R3.
    23. 

  23. 

  24.   KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
    25. 

  25.   property inside the device tree's /hypervisor node.
    26. 

  26.   For more information refer to Documentation/virtual/kvm/ppc-pv.txt
    27. 

  27. 

  28. KVM Hypercalls Documentation
    29. 

  29. ===========================
    30. 

  30. The template for each hypercall is:
    31. 

  31. 1. Hypercall name.
    32. 

  32. 2. Architecture(s)
    33. 

  33. 3. Status (deprecated, obsolete, active)
    34. 

  34. 4. Purpose
    35. 

  35. 

  36. 1. KVM_HC_VAPIC_POLL_IRQ
    37. 

  37. ------------------------
    38. 

  38. Architecture: x86
    39. 

  39. Status: active
    40. 

  40. Purpose: Trigger guest exit so that the host can check for pending
    41. 

  41. interrupts on reentry.
    42. 

  42. 

  43. 2. KVM_HC_MMU_OP
    44. 

  44. ------------------------
    45. 

  45. Architecture: x86
    46. 

  46. Status: deprecated.
    47. 

  47. Purpose: Support MMU operations such as writing to PTE,
    48. 

  48. flushing TLB, release PT.
    49. 

  49. 

  50. 3. KVM_HC_FEATURES
    51. 

  51. ------------------------
    52. 

  52. Architecture: PPC
    53. 

  53. Status: active
    54. 

  54. Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
    55. 

  55. used to enumerate which hypercalls are available. On PPC, either device tree
    56. 

  56. based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
    57. 

  57. mechanism (which is this hypercall) can be used.
    58. 

  58. 

  59. 4. KVM_HC_PPC_MAP_MAGIC_PAGE
    60. 

  60. ------------------------
    61. 

  61. Architecture: PPC
    62. 

  62. Status: active
    63. 

  63. Purpose: To enable communication between the hypervisor and guest there is a
    64. 

  64. shared page that contains parts of supervisor visible register state.
    65. 

  65. The guest can map this shared page to access its supervisor register through
    66. 

  66. memory using this hypercall.
    67.