84 lines
3.0 KiB
Plaintext
84 lines
3.0 KiB
Plaintext
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Linux KVM Hypercall:
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===================
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X86:
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KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
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instruction. The hypervisor can replace it with instructions that are
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guaranteed to be supported.
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Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
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The hypercall number should be placed in rax and the return value will be
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placed in rax. No other registers will be clobbered unless explicitly stated
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by the particular hypercall.
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S390:
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R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
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number. The return value is written to R2.
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S390 uses diagnose instruction as hypercall (0x500) along with hypercall
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number in R1.
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For further information on the S390 diagnose call as supported by KVM,
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refer to Documentation/virtual/kvm/s390-diag.txt.
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PowerPC:
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It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
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Return value is placed in R3.
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KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
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property inside the device tree's /hypervisor node.
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For more information refer to Documentation/virtual/kvm/ppc-pv.txt
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KVM Hypercalls Documentation
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===========================
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The template for each hypercall is:
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1. Hypercall name.
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2. Architecture(s)
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3. Status (deprecated, obsolete, active)
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4. Purpose
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1. KVM_HC_VAPIC_POLL_IRQ
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------------------------
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Architecture: x86
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Status: active
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Purpose: Trigger guest exit so that the host can check for pending
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interrupts on reentry.
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2. KVM_HC_MMU_OP
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------------------------
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Architecture: x86
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Status: deprecated.
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Purpose: Support MMU operations such as writing to PTE,
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flushing TLB, release PT.
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3. KVM_HC_FEATURES
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------------------------
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Architecture: PPC
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Status: active
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Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
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used to enumerate which hypercalls are available. On PPC, either device tree
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based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
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mechanism (which is this hypercall) can be used.
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4. KVM_HC_PPC_MAP_MAGIC_PAGE
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------------------------
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Architecture: PPC
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Status: active
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Purpose: To enable communication between the hypervisor and guest there is a
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shared page that contains parts of supervisor visible register state.
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The guest can map this shared page to access its supervisor register through
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memory using this hypercall.
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5. KVM_HC_KICK_CPU
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------------------------
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Architecture: x86
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Status: active
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Purpose: Hypercall used to wakeup a vcpu from HLT state
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Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
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kernel mode for an event to occur (ex: a spinlock to become available) can
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execute HLT instruction once it has busy-waited for more than a threshold
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time-interval. Execution of HLT instruction would cause the hypervisor to put
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the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
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same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
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specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
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is used in the hypercall for future use.
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