1 .. SPDX-License-Identifier: GPL-2.0
2
3 Paravirtualized time support for arm64
4 ======================================
5
6 Arm specification DEN0057/A defines a standard
7 support for AArch64 guests:
8
9 https://developer.arm.com/docs/den0057/a
10
11 KVM/arm64 implements the stolen time part of t
12 some hypervisor service calls to support a par
13 view of the amount of time stolen from its exe
14
15 Two new SMCCC compatible hypercalls are define
16
17 * PV_TIME_FEATURES: 0xC5000020
18 * PV_TIME_ST: 0xC5000021
19
20 These are only available in the SMC64/HVC64 ca
21 paravirtualized time is not available to 32 bi
22 the PV_TIME_FEATURES hypercall should be probe
23 ARCH_FEATURES mechanism before calling it.
24
25 PV_TIME_FEATURES
26
27 ============= ======== ================
28 Function ID: (uint32) 0xC5000020
29 PV_call_id: (uint32) The function to
30 Currently only P
31 Return value: (int64) NOT_SUPPORTED (-
32 PV-time feature
33 ============= ======== ================
34
35 PV_TIME_ST
36
37 ============= ======== ================
38 Function ID: (uint32) 0xC5000021
39 Return value: (int64) IPA of the stole
40 VCPU. On failure
41 NOT_SUPPORTED (-
42 ============= ======== ================
43
44 The IPA returned by PV_TIME_ST should be mappe
45 with inner and outer write back caching attrib
46 domain. A total of 16 bytes from the IPA retur
47 meaningfully filled by the hypervisor (see str
48
49 PV_TIME_ST returns the structure for the calli
50
51 Stolen Time
52 -----------
53
54 The structure pointed to by the PV_TIME_ST hyp
55
56 +-------------+-------------+-------------+---
57 | Field | Byte Length | Byte Offset | De
58 +=============+=============+=============+===
59 | Revision | 4 | 0 | Mu
60 +-------------+-------------+-------------+---
61 | Attributes | 4 | 4 | Mu
62 +-------------+-------------+-------------+---
63 | Stolen time | 8 | 8 | St
64 | | | | na
65 | | | | mu
66 | | | | wa
67 | | | | ru
68 +-------------+-------------+-------------+---
69
70 All values in the structure are stored little-
71
72 The structure will be updated by the hyperviso
73 will be present within a reserved region of th
74 guest. The guest should not attempt to write i
75 structure per VCPU of the guest.
76
77 It is advisable that one or more 64k pages are
78 these structures and not used for other purpos
79 the region using 64k pages and avoids conflict
80
81 For the user space interface see
82 :ref:`Documentation/virt/kvm/devices/vcpu.rst
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