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+Linux KVM Hypercall:
+ KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall
+ instruction. The hypervisor can replace it with instructions that are
+ guaranteed to be supported.
+ Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively.
+ The hypercall number should be placed in rax and the return value will be
+ placed in rax. No other registers will be clobbered unless explicitly stated
+ by the particular hypercall.
+ R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall
+ number. The return value is written to R2.
+ S390 uses diagnose instruction as hypercall (0x500) along with hypercall
+ number in R1.
+ PowerPC:
+ It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers.
+ Return value is placed in R3.
+ KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions'
+ property inside the device tree's /hypervisor node.
+ For more information refer to Documentation/virtual/kvm/ppc-pv.txt
+KVM Hypercalls Documentation
+The template for each hypercall is:
+1. Hypercall name.
+2. Architecture(s)
+3. Status (deprecated, obsolete, active)
+4. Purpose
+Architecture: x86
+Status: active
+Purpose: Trigger guest exit so that the host can check for pending
+interrupts on reentry.
+Architecture: x86
+Status: deprecated.
+Purpose: Support MMU operations such as writing to PTE,
+flushing TLB, release PT.
+Architecture: PPC
+Status: active
+Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid
+used to enumerate which hypercalls are available. On PPC, either device tree
+based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration
+mechanism (which is this hypercall) can be used.
+Architecture: PPC
+Status: active
+Purpose: To enable communication between the hypervisor and guest there is a
+shared page that contains parts of supervisor visible register state.
+The guest can map this shared page to access its supervisor register through
+memory using this hypercall.