.. SPDX-License-Identifier: GPL-2.0

====================
APEI Error INJection
====================

EINJ provides a hardware error injection mechanism. It is very useful
for debugging and testing APEI and RAS features in general.

You need to check whether your BIOS supports EINJ first. For that, look
for early boot messages similar to this one::

  ACPI: EINJ 0x000000007370A000 000150 (v01 INTEL           00000001 INTL 00000001)

which shows that the BIOS is exposing an EINJ table - it is the
mechanism through which the injection is done.

Alternatively, look in /sys/firmware/acpi/tables for an "EINJ" file,
which is a different representation of the same thing.

It doesn't necessarily mean that EINJ is not supported if those above
don't exist: before you give up, go into BIOS setup to see if the BIOS
has an option to enable error injection. Look for something called WHEA
or similar. Often, you need to enable an ACPI5 support option prior, in
order to see the APEI,EINJ,... functionality supported and exposed by
the BIOS menu.

To use EINJ, make sure the following are options enabled in your kernel
configuration::

  CONFIG_DEBUG_FS
  CONFIG_ACPI_APEI
  CONFIG_ACPI_APEI_EINJ

The EINJ user interface is in <debugfs mount point>/apei/einj.

The following files belong to it:

- available_error_type

  This file shows which error types are supported:

  ================  ===================================
  Error Type Value	Error Description
  ================  ===================================
  0x00000001        Processor Correctable
  0x00000002        Processor Uncorrectable non-fatal
  0x00000004        Processor Uncorrectable fatal
  0x00000008        Memory Correctable
  0x00000010        Memory Uncorrectable non-fatal
  0x00000020        Memory Uncorrectable fatal
  0x00000040        PCI Express Correctable
  0x00000080        PCI Express Uncorrectable non-fatal
  0x00000100        PCI Express Uncorrectable fatal
  0x00000200        Platform Correctable
  0x00000400        Platform Uncorrectable non-fatal
  0x00000800        Platform Uncorrectable fatal
  ================  ===================================

  The format of the file contents are as above, except present are only
  the available error types.

- error_type

  Set the value of the error type being injected. Possible error types
  are defined in the file available_error_type above.

- error_inject

  Write any integer to this file to trigger the error injection. Make
  sure you have specified all necessary error parameters, i.e. this
  write should be the last step when injecting errors.

- flags

  Present for kernel versions 3.13 and above. Used to specify which
  of param{1..4} are valid and should be used by the firmware during
  injection. Value is a bitmask as specified in ACPI5.0 spec for the
  SET_ERROR_TYPE_WITH_ADDRESS data structure:

    Bit 0
      Processor APIC field valid (see param3 below).
    Bit 1
      Memory address and mask valid (param1 and param2).
    Bit 2
      PCIe (seg,bus,dev,fn) valid (see param4 below).

  If set to zero, legacy behavior is mimicked where the type of
  injection specifies just one bit set, and param1 is multiplexed.

- param1

  This file is used to set the first error parameter value. Its effect
  depends on the error type specified in error_type. For example, if
  error type is memory related type, the param1 should be a valid
  physical memory address. [Unless "flag" is set - see above]

- param2

  Same use as param1 above. For example, if error type is of memory
  related type, then param2 should be a physical memory address mask.
  Linux requires page or narrower granularity, say, 0xfffffffffffff000.

- param3

  Used when the 0x1 bit is set in "flags" to specify the APIC id

- param4
  Used when the 0x4 bit is set in "flags" to specify target PCIe device

- notrigger

  The error injection mechanism is a two-step process. First inject the
  error, then perform some actions to trigger it. Setting "notrigger"
  to 1 skips the trigger phase, which *may* allow the user to cause the
  error in some other context by a simple access to the CPU, memory
  location, or device that is the target of the error injection. Whether
  this actually works depends on what operations the BIOS actually
  includes in the trigger phase.

BIOS versions based on the ACPI 4.0 specification have limited options
in controlling where the errors are injected. Your BIOS may support an
extension (enabled with the param_extension=1 module parameter, or boot
command line einj.param_extension=1). This allows the address and mask
for memory injections to be specified by the param1 and param2 files in
apei/einj.

BIOS versions based on the ACPI 5.0 specification have more control over
the target of the injection. For processor-related errors (type 0x1, 0x2
and 0x4), you can set flags to 0x3 (param3 for bit 0, and param1 and
param2 for bit 1) so that you have more information added to the error
signature being injected. The actual data passed is this::

	memory_address = param1;
	memory_address_range = param2;
	apicid = param3;
	pcie_sbdf = param4;

For memory errors (type 0x8, 0x10 and 0x20) the address is set using
param1 with a mask in param2 (0x0 is equivalent to all ones). For PCI
express errors (type 0x40, 0x80 and 0x100) the segment, bus, device and
function are specified using param1::

         31     24 23    16 15    11 10      8  7        0
	+-------------------------------------------------+
	| segment |   bus  | device | function | reserved |
	+-------------------------------------------------+

Anyway, you get the idea, if there's doubt just take a look at the code
in drivers/acpi/apei/einj.c.

An ACPI 5.0 BIOS may also allow vendor-specific errors to be injected.
In this case a file named vendor will contain identifying information
from the BIOS that hopefully will allow an application wishing to use
the vendor-specific extension to tell that they are running on a BIOS
that supports it. All vendor extensions have the 0x80000000 bit set in
error_type. A file vendor_flags controls the interpretation of param1
and param2 (1 = PROCESSOR, 2 = MEMORY, 4 = PCI). See your BIOS vendor
documentation for details (and expect changes to this API if vendors
creativity in using this feature expands beyond our expectations).


An error injection example::

  # cd /sys/kernel/debug/apei/einj
  # cat available_error_type		# See which errors can be injected
  0x00000002	Processor Uncorrectable non-fatal
  0x00000008	Memory Correctable
  0x00000010	Memory Uncorrectable non-fatal
  # echo 0x12345000 > param1		# Set memory address for injection
  # echo $((-1 << 12)) > param2		# Mask 0xfffffffffffff000 - anywhere in this page
  # echo 0x8 > error_type			# Choose correctable memory error
  # echo 1 > error_inject			# Inject now

You should see something like this in dmesg::

  [22715.830801] EDAC sbridge MC3: HANDLING MCE MEMORY ERROR
  [22715.834759] EDAC sbridge MC3: CPU 0: Machine Check Event: 0 Bank 7: 8c00004000010090
  [22715.834759] EDAC sbridge MC3: TSC 0
  [22715.834759] EDAC sbridge MC3: ADDR 12345000 EDAC sbridge MC3: MISC 144780c86
  [22715.834759] EDAC sbridge MC3: PROCESSOR 0:306e7 TIME 1422553404 SOCKET 0 APIC 0
  [22716.616173] EDAC MC3: 1 CE memory read error on CPU_SrcID#0_Channel#0_DIMM#0 (channel:0 slot:0 page:0x12345 offset:0x0 grain:32 syndrome:0x0 -  area:DRAM err_code:0001:0090 socket:0 channel_mask:1 rank:0)

For more information about EINJ, please refer to ACPI specification
version 4.0, section 17.5 and ACPI 5.0, section 18.6.