KVM: Add ppc hypercall documentation

That way we can inject an arbitrary amount of code as replacement for a single

That way we can inject an arbitrary amount of code as replacement for a single

instruction. This allows us to check for pending interrupts when setting EE=1

instruction. This allows us to check for pending interrupts when setting EE=1

for example.

for example.

Hypercall ABIs in KVM on PowerPC

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1) KVM hypercalls (ePAPR)

These are ePAPR compliant hypercall implementation (mentioned above). Even

generic hypercalls are implemented here, like the ePAPR idle hcall. These are

available on all targets.

2) PAPR hypercalls

PAPR hypercalls are needed to run server PowerPC PAPR guests (-M pseries in QEMU).

These are the same hypercalls that pHyp, the POWER hypervisor implements. Some of

them are handled in the kernel, some are handled in user space. This is only

available on book3s_64.

3) OSI hypercalls

Mac-on-Linux is another user of KVM on PowerPC, which has its own hypercall (long

before KVM). This is supported to maintain compatibility. All these hypercalls get

forwarded to user space. This is only useful on book3s_32, but can be used with

book3s_64 as well.