Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 The s390 DIAGNOSE call on KVM 2 ============================= 3 4 KVM on s390 supports the DIAGNOSE call for making hypercalls, both for 5 native hypercalls and for selected hypercalls found on other s390 6 hypervisors. 7 8 Note that bits are numbered as by the usual s390 convention (most significant 9 bit on the left). 10 11 12 General remarks 13 --------------- 14 15 DIAGNOSE calls by the guest cause a mandatory intercept. This implies 16 all supported DIAGNOSE calls need to be handled by either KVM or its 17 userspace. 18 19 All DIAGNOSE calls supported by KVM use the RS-a format: 20 21 -------------------------------------- 22 | '83' | R1 | R3 | B2 | D2 | 23 -------------------------------------- 24 0 8 12 16 20 31 25 26 The second-operand address (obtained by the base/displacement calculation) 27 is not used to address data. Instead, bits 48-63 of this address specify 28 the function code, and bits 0-47 are ignored. 29 30 The supported DIAGNOSE function codes vary by the userspace used. For 31 DIAGNOSE function codes not specific to KVM, please refer to the 32 documentation for the s390 hypervisors defining them. 33 34 35 DIAGNOSE function code 'X'500' - KVM virtio functions 36 ----------------------------------------------------- 37 38 If the function code specifies 0x500, various virtio-related functions 39 are performed. 40 41 General register 1 contains the virtio subfunction code. Supported 42 virtio subfunctions depend on KVM's userspace. Generally, userspace 43 provides either s390-virtio (subcodes 0-2) or virtio-ccw (subcode 3). 44 45 Upon completion of the DIAGNOSE instruction, general register 2 contains 46 the function's return code, which is either a return code or a subcode 47 specific value. 48 49 Subcode 0 - s390-virtio notification and early console printk 50 Handled by userspace. 51 52 Subcode 1 - s390-virtio reset 53 Handled by userspace. 54 55 Subcode 2 - s390-virtio set status 56 Handled by userspace. 57 58 Subcode 3 - virtio-ccw notification 59 Handled by either userspace or KVM (ioeventfd case). 60 61 General register 2 contains a subchannel-identification word denoting 62 the subchannel of the virtio-ccw proxy device to be notified. 63 64 General register 3 contains the number of the virtqueue to be notified. 65 66 General register 4 contains a 64bit identifier for KVM usage (the 67 kvm_io_bus cookie). If general register 4 does not contain a valid 68 identifier, it is ignored. 69 70 After completion of the DIAGNOSE call, general register 2 may contain 71 a 64bit identifier (in the kvm_io_bus cookie case). 72 73 See also the virtio standard for a discussion of this hypercall. 74 75 76 DIAGNOSE function code 'X'501 - KVM breakpoint 77 ---------------------------------------------- 78 79 If the function code specifies 0x501, breakpoint functions may be performed. 80 This function code is handled by userspace. 81 82 This diagnose function code has no subfunctions and uses no parameters.