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diff --git a/Documentation/virt/kvm/loongarch/hypercalls.rst b/Documentation/virt/kvm/loongarch/hypercalls.rst new file mode 100644 index 000000000000..2d6b94031f1b --- /dev/null +++ b/Documentation/virt/kvm/loongarch/hypercalls.rst @@ -0,0 +1,89 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +The LoongArch paravirtual interface +=================================== + +KVM hypercalls use the HVCL instruction with code 0x100 and the hypercall +number is put in a0. Up to five arguments may be placed in registers a1 - a5. +The return value is placed in v0 (an alias of a0). + +Source code for this interface can be found in arch/loongarch/kvm*. + +Querying for existence +====================== + +To determine if the host is running on KVM, we can utilize the cpucfg() +function at index CPUCFG_KVM_BASE (0x40000000). + +The CPUCFG_KVM_BASE range, spanning from 0x40000000 to 0x400000FF, The +CPUCFG_KVM_BASE range between 0x40000000 - 0x400000FF is marked as reserved. +Consequently, all current and future processors will not implement any +feature within this range. + +On a KVM-virtualized Linux system, a read operation on cpucfg() at index +CPUCFG_KVM_BASE (0x40000000) returns the magic string 'KVM\0'. + +Once you have determined that your host is running on a paravirtualization- +capable KVM, you may now use hypercalls as described below. + +KVM hypercall ABI +================= + +The KVM hypercall ABI is simple, with one scratch register a0 (v0) and at most +five generic registers (a1 - a5) used as input parameters. The FP (Floating- +point) and vector registers are not utilized as input registers and must +remain unmodified during a hypercall. + +Hypercall functions can be inlined as it only uses one scratch register. + +The parameters are as follows: + + ======== ================= ================ + Register IN OUT + ======== ================= ================ + a0 function number Return code + a1 1st parameter - + a2 2nd parameter - + a3 3rd parameter - + a4 4th parameter - + a5 5th parameter - + ======== ================= ================ + +The return codes may be one of the following: + + ==== ========================= + Code Meaning + ==== ========================= + 0 Success + -1 Hypercall not implemented + -2 Bad Hypercall parameter + ==== ========================= + +KVM Hypercalls Documentation +============================ + +The template for each hypercall is as follows: + +1. Hypercall name +2. Purpose + +1. KVM_HCALL_FUNC_IPI +------------------------ + +:Purpose: Send IPIs to multiple vCPUs. + +- a0: KVM_HCALL_FUNC_IPI +- a1: Lower part of the bitmap for destination physical CPUIDs +- a2: Higher part of the bitmap for destination physical CPUIDs +- a3: The lowest physical CPUID in the bitmap + +The hypercall lets a guest send multiple IPIs (Inter-Process Interrupts) with +at most 128 destinations per hypercall. The destinations are represented in a +bitmap contained in the first two input registers (a1 and a2). + +Bit 0 of a1 corresponds to the physical CPUID in the third input register (a3) +and bit 1 corresponds to the physical CPUID in a3+1, and so on. + +PV IPI on LoongArch includes both PV IPI multicast sending and PV IPI receiving, +and SWI is used for PV IPI inject since there is no VM-exits accessing SWI registers. |