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1 APEI tables generating and CPER record
2 ======================================
3
4 ..
5 Copyright (c) 2020 HUAWEI TECHNOLOGIES CO., LTD.
6
7 This work is licensed under the terms of the GNU GPL, version 2 or later.
8 See the COPYING file in the top-level directory.
9
10 Design Details
11 --------------
12
13 ::
14
15 etc/acpi/tables etc/hardware_errors
16 ==================== ===============================
17 + +--------------------------+ +----------------------------+
18 | | HEST | +--------->| error_block_address1 |------+
19 | +--------------------------+ | +----------------------------+ |
20 | | GHES1 | | +------->| error_block_address2 |------+-+
21 | +--------------------------+ | | +----------------------------+ | |
22 | | ................. | | | | .............. | | |
23 | | error_status_address-----+-+ | -----------------------------+ | |
24 | | ................. | | +--->| error_block_addressN |------+-+---+
25 | | read_ack_register--------+-+ | | +----------------------------+ | | |
26 | | read_ack_preserve | +-+---+--->| read_ack_register1 | | | |
27 | | read_ack_write | | | +----------------------------+ | | |
28 + +--------------------------+ | +-+--->| read_ack_register2 | | | |
29 | | GHES2 | | | | +----------------------------+ | | |
30 + +--------------------------+ | | | | ............. | | | |
31 | | ................. | | | | +----------------------------+ | | |
32 | | error_status_address-----+---+ | | +->| read_ack_registerN | | | |
33 | | ................. | | | | +----------------------------+ | | |
34 | | read_ack_register--------+-----+ | | |Generic Error Status Block 1|<-----+ | |
35 | | read_ack_preserve | | | |-+------------------------+-+ | |
36 | | read_ack_write | | | | | CPER | | | |
37 + +--------------------------| | | | | CPER | | | |
38 | | ............... | | | | | .... | | | |
39 + +--------------------------+ | | | | CPER | | | |
40 | | GHESN | | | |-+------------------------+-| | |
41 + +--------------------------+ | | |Generic Error Status Block 2|<-------+ |
42 | | ................. | | | |-+------------------------+-+ |
43 | | error_status_address-----+-------+ | | | CPER | | |
44 | | ................. | | | | CPER | | |
45 | | read_ack_register--------+---------+ | | .... | | |
46 | | read_ack_preserve | | | CPER | | |
47 | | read_ack_write | +-+------------------------+-+ |
48 + +--------------------------+ | .......... | |
49 |----------------------------+ |
50 |Generic Error Status Block N |<----------+
51 |-+-------------------------+-+
52 | | CPER | |
53 | | CPER | |
54 | | .... | |
55 | | CPER | |
56 +-+-------------------------+-+
57
58
59 (1) QEMU generates the ACPI HEST table. This table goes in the current
60 "etc/acpi/tables" fw_cfg blob. Each error source has different
61 notification types.
62
63 (2) A new fw_cfg blob called "etc/hardware_errors" is introduced. QEMU
64 also needs to populate this blob. The "etc/hardware_errors" fw_cfg blob
65 contains an address registers table and an Error Status Data Block table.
66
67 (3) The address registers table contains N Error Block Address entries
68 and N Read Ack Register entries. The size for each entry is 8-byte.
69 The Error Status Data Block table contains N Error Status Data Block
70 entries. The size for each entry is defined at the source code as
71 ACPI_GHES_MAX_RAW_DATA_LENGTH (currently 1024 bytes). The total size
72 for the "etc/hardware_errors" fw_cfg blob is
73 (N * 8 * 2 + N * ACPI_GHES_MAX_RAW_DATA_LENGTH) bytes.
74 N is the number of the kinds of hardware error sources.
75
76 (4) QEMU generates the ACPI linker/loader script for the firmware. The
77 firmware pre-allocates memory for "etc/acpi/tables", "etc/hardware_errors"
78 and copies blob contents there.
79
80 (5) QEMU generates N ADD_POINTER commands, which patch addresses in the
81 "error_status_address" fields of the HEST table with a pointer to the
82 corresponding "address registers" in the "etc/hardware_errors" blob.
83
84 (6) QEMU generates N ADD_POINTER commands, which patch addresses in the
85 "read_ack_register" fields of the HEST table with a pointer to the
86 corresponding "read_ack_register" within the "etc/hardware_errors" blob.
87
88 (7) QEMU generates N ADD_POINTER commands for the firmware, which patch
89 addresses in the "error_block_address" fields with a pointer to the
90 respective "Error Status Data Block" in the "etc/hardware_errors" blob.
91
92 (8) QEMU defines a third and write-only fw_cfg blob to store the location
93 where the error block offsets, read ack registers and CPER records are
94 stored.
95
96 Up to QEMU 9.2, the location was at "etc/hardware_errors_addr", and
97 contains a GPA for the beginning of "etc/hardware_errors".
98
99 Newer versions place the location at "etc/acpi_table_hest_addr",
100 pointing to the GPA of the HEST table.
101
102 Using above mentioned 'fw_cfg' files, the firmware can send back the
103 guest-side allocation addresses to QEMU. They contain a 8-byte entry.
104 QEMU generates a single WRITE_POINTER command for the firmware. The
105 firmware will write back the start address of either "etc/hardware_errors"
106 or HEST table at the corresponding fw_cfg file.
107
108 (9) When QEMU gets a SIGBUS from the kernel, QEMU writes CPER into corresponding
109 "Error Status Data Block", guest memory, and then injects platform specific
110 interrupt (in case of arm/virt machine it's Synchronous External Abort) as a
111 notification which is necessary for notifying the guest.
112
113 (10) This notification (in virtual hardware) will be handled by the guest
114 kernel, on receiving notification, guest APEI driver could read the CPER error
115 and take appropriate action.
116
117 (11) kvm_arch_on_sigbus_vcpu() reports RAS errors via a SEA notifications,
118 when a SIGBUS event is triggered.