1 .. SPDX-License-Identifier: GPL-2.0 2 3 =================================== 4 The LoongArch paravirtual interface 5 =================================== 6 7 KVM hypercalls use the HVCL instruction with code 0x100 and the hypercall 8 number is put in a0. Up to five arguments may be placed in registers a1 - a5. 9 The return value is placed in v0 (an alias of a0). 10 11 Source code for this interface can be found in arch/loongarch/kvm*. 12 13 Querying for existence 14 ====================== 15 16 To determine if the host is running on KVM, we can utilize the cpucfg() 17 function at index CPUCFG_KVM_BASE (0x40000000). 18 19 The CPUCFG_KVM_BASE range, spanning from 0x40000000 to 0x400000FF, The 20 CPUCFG_KVM_BASE range between 0x40000000 - 0x400000FF is marked as reserved. 21 Consequently, all current and future processors will not implement any 22 feature within this range. 23 24 On a KVM-virtualized Linux system, a read operation on cpucfg() at index 25 CPUCFG_KVM_BASE (0x40000000) returns the magic string 'KVM\0'. 26 27 Once you have determined that your host is running on a paravirtualization- 28 capable KVM, you may now use hypercalls as described below. 29 30 KVM hypercall ABI 31 ================= 32 33 The KVM hypercall ABI is simple, with one scratch register a0 (v0) and at most 34 five generic registers (a1 - a5) used as input parameters. The FP (Floating- 35 point) and vector registers are not utilized as input registers and must 36 remain unmodified during a hypercall. 37 38 Hypercall functions can be inlined as it only uses one scratch register. 39 40 The parameters are as follows: 41 42 ======== ================= ================ 43 Register IN OUT 44 ======== ================= ================ 45 a0 function number Return code 46 a1 1st parameter - 47 a2 2nd parameter - 48 a3 3rd parameter - 49 a4 4th parameter - 50 a5 5th parameter - 51 ======== ================= ================ 52 53 The return codes may be one of the following: 54 55 ==== ========================= 56 Code Meaning 57 ==== ========================= 58 0 Success 59 -1 Hypercall not implemented 60 -2 Bad Hypercall parameter 61 ==== ========================= 62 63 KVM Hypercalls Documentation 64 ============================ 65 66 The template for each hypercall is as follows: 67 68 1. Hypercall name 69 2. Purpose 70 71 1. KVM_HCALL_FUNC_IPI 72 ------------------------ 73 74 :Purpose: Send IPIs to multiple vCPUs. 75 76 - a0: KVM_HCALL_FUNC_IPI 77 - a1: Lower part of the bitmap for destination physical CPUIDs 78 - a2: Higher part of the bitmap for destination physical CPUIDs 79 - a3: The lowest physical CPUID in the bitmap 80 81 The hypercall lets a guest send multiple IPIs (Inter-Process Interrupts) with 82 at most 128 destinations per hypercall. The destinations are represented in a 83 bitmap contained in the first two input registers (a1 and a2). 84 85 Bit 0 of a1 corresponds to the physical CPUID in the third input register (a3) 86 and bit 1 corresponds to the physical CPUID in a3+1, and so on. 87 88 PV IPI on LoongArch includes both PV IPI multicast sending and PV IPI receiving, 89 and SWI is used for PV IPI inject since there is no VM-exits accessing SWI registers.
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