1 .. SPDX-License-Identifier: GPL-2.0
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4 s390 (IBM Z) Ultravisor and Protected VMs
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6
7 Summary
8 -------
9 Protected virtual machines (PVM) are KVM VMs t
10 access VM state like guest memory or guest reg
11 PVMs are mostly managed by a new entity called
12 provides an API that can be used by PVMs and K
13 actions.
14
15 Each guest starts in non-protected mode and th
16 transition into protected mode. On transition,
17 and its VCPUs with the Ultravisor and prepares
18 it.
19
20 The Ultravisor will secure and decrypt the gue
21 (i.e. kernel/initrd). It will safeguard state
22 starts/stops and injected interrupts while the
23
24 As access to the guest's state, such as the SI
25 normally needed to be able to run a VM, some c
26 the behavior of the SIE instruction. A new for
27 has been introduced, where some fields have di
28 PVM. SIE exits are minimized as much as possib
29 reduce exposed guest state.
30
31
32 Interrupt injection
33 -------------------
34 Interrupt injection is safeguarded by the Ultr
35 have access to the VCPUs' lowcores, injection
36 format 4 state description.
37
38 Machine check, external, IO and restart interr
39 injected on SIE entry via a bit in the interru
40 field (offset 0x54). If the guest cpu is not e
41 at the time of injection, a validity intercept
42 format 4 state description contains fields in
43 block where data associated with the interrupt
44
45 Program and Service Call exceptions have anoth
46 safeguarding; they can only be injected for in
47 been intercepted into KVM. The exceptions need
48 of an instruction emulation by KVM, e.g. we ca
49 addressing exception as they are reported by S
50 access to the guest memory.
51
52
53 Mask notification interceptions
54 -------------------------------
55 KVM cannot intercept lctl(g) and lpsw(e) anymo
56 notified when a PVM enables a certain class of
57 replacement, two new interception codes have b
58 indicating that the contents of CRs 0, 6, or 1
59 indicating different interruption subclasses;
60 PSW bit 13 has been changed, indicating that a
61 intervention was requested and those are now e
62
63 Instruction emulation
64 ---------------------
65 With the format 4 state description for PVMs,
66 interprets more instructions than it does with
67 to interpret every instruction, but needs to h
68 therefore, the SIE and the ultravisor safeguar
69
70 The control structures associated with SIE pro
71 Instruction Data Area (SIDA), the Interception
72 Secure Interception General Register Save Area
73 the instruction data, such as I/O data structu
74 Instruction data is copied to and from the SID
75 GRs are put into / retrieved from the Secure I
76 Register Save Area.
77
78 Only GR values needed to emulate an instructio
79 save area and the real register numbers will b
80
81 The Interception Parameters state description
82 the bytes of the instruction text, but with pr
83 instead of the actual ones. I.e. each instruct
84 instruction text, in order not to leak guest i
85 This also implies that the register content th
86 may be in r<m> from the hypervisor's point of
87
88 The Secure Instruction Data Area contains inst
89 data. Instruction data, i.e. data being refere
90 like the SCCB for sclp, is moved via the SIDA.
91 intercepted, the SIE will only allow data and
92 this instruction to be moved to the guest via
93 discussed before. Other data is either ignored
94 interceptions.
95
96
97 Instruction emulation interceptions
98 -----------------------------------
99 There are two types of SIE secure instruction
100 and the notification type. Normal secure instr
101 make the guest pending for instruction complet
102 instruction type, i.e. on SIE entry it is atte
103 emulation of the instruction with the data pro
104 be a program exception or instruction completi
105
106 The notification type intercepts inform KVM ab
107 changes due to guest instruction interpretatio
108 is recognized, for example, for the store pref
109 the new lowcore location. On SIE reentry, any
110 is ignored and execution continues as if the g
111 completed. For that reason KVM is not allowed
112 interrupt.
113
114 Links
115 -----
116 `KVM Forum 2019 presentation <https://static.s
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