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https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=403205
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Fox Snowpatch committed Apr 16, 2024
1 parent 77dff0c commit a21dba4
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11 changes: 11 additions & 0 deletions Documentation/ABI/testing/sysfs-kernel-fadump
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Expand Up @@ -38,3 +38,14 @@ Contact: linuxppc-dev@lists.ozlabs.org
Description: read only
Provide information about the amount of memory reserved by
FADump to save the crash dump in bytes.

What: /sys/kernel/fadump/hotplug_ready
Date: Apr 2024
Contact: linuxppc-dev@lists.ozlabs.org
Description: read only
Kdump udev rule re-registers fadump on memory add/remove events,
primarily to update the elfcorehdr. This sysfs indicates the
kdump udev rule that fadump re-registration is not required on
memory add/remove events because elfcorehdr is now prepared in
the second/fadump kernel.
User: kexec-tools
91 changes: 42 additions & 49 deletions Documentation/arch/powerpc/firmware-assisted-dump.rst
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Expand Up @@ -134,12 +134,12 @@ that are run. If there is dump data, then the
memory is held.

If there is no waiting dump data, then only the memory required to
hold CPU state, HPTE region, boot memory dump, FADump header and
elfcore header, is usually reserved at an offset greater than boot
memory size (see Fig. 1). This area is *not* released: this region
will be kept permanently reserved, so that it can act as a receptacle
for a copy of the boot memory content in addition to CPU state and
HPTE region, in the case a crash does occur.
hold CPU state, HPTE region, boot memory dump, and FADump header is
usually reserved at an offset greater than boot memory size (see Fig. 1).
This area is *not* released: this region will be kept permanently
reserved, so that it can act as a receptacle for a copy of the boot
memory content in addition to CPU state and HPTE region, in the case
a crash does occur.

Since this reserved memory area is used only after the system crash,
there is no point in blocking this significant chunk of memory from
Expand All @@ -153,22 +153,22 @@ that were present in CMA region::

o Memory Reservation during first kernel

Low memory Top of memory
0 boot memory size |<--- Reserved dump area --->| |
| | | Permanent Reservation | |
V V | | V
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| | |///|////| DUMP | HDR | ELF |////| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| ^ ^ ^ ^ ^
| | | | | |
\ CPU HPTE / | |
------------------------------ | |
Boot memory content gets transferred | |
to reserved area by firmware at the | |
time of crash. | |
FADump Header |
(meta area) |
Low memory Top of memory
0 boot memory size |<------ Reserved dump area ----->| |
| | | Permanent Reservation | |
V V | | V
+-----------+-----/ /---+---+----+-----------+-------+----+-----+
| | |///|////| DUMP | HDR |////| |
+-----------+-----/ /---+---+----+-----------+-------+----+-----+
| ^ ^ ^ ^ ^
| | | | | |
\ CPU HPTE / | |
-------------------------------- | |
Boot memory content gets transferred | |
to reserved area by firmware at the | |
time of crash. | |
FADump Header |
(meta area) |
|
|
Metadata: This area holds a metadata structure whose
Expand All @@ -186,20 +186,33 @@ that were present in CMA region::
0 boot memory size |
| |<------------ Crash preserved area ------------>|
V V |<--- Reserved dump area --->| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| | |///|////| DUMP | HDR | ELF |////| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| |
V V
Used by second /proc/vmcore
kernel to boot
+----+---+--+-----/ /---+---+----+-------+-----+-----+-------+
| |ELF| | |///|////| DUMP | HDR |/////| |
+----+---+--+-----/ /---+---+----+-------+-----+-----+-------+
| | | | | |
----- ------------------------------ ---------------
\ | |
\ | |
\ | |
\ | ----------------------------
\ | /
\ | /
\ | /
/proc/vmcore


+---+
|///| -> Regions (CPU, HPTE & Metadata) marked like this in the above
+---+ figures are not always present. For example, OPAL platform
does not have CPU & HPTE regions while Metadata region is
not supported on pSeries currently.

+---+
|ELF| -> elfcorehdr, it is created in second kernel after crash.
+---+

Note: Memory from 0 to the boot memory size is used by second kernel

Fig. 2


Expand Down Expand Up @@ -353,26 +366,6 @@ TODO:
- Need to come up with the better approach to find out more
accurate boot memory size that is required for a kernel to
boot successfully when booted with restricted memory.
- The FADump implementation introduces a FADump crash info structure
in the scratch area before the ELF core header. The idea of introducing
this structure is to pass some important crash info data to the second
kernel which will help second kernel to populate ELF core header with
correct data before it gets exported through /proc/vmcore. The current
design implementation does not address a possibility of introducing
additional fields (in future) to this structure without affecting
compatibility. Need to come up with the better approach to address this.

The possible approaches are:

1. Introduce version field for version tracking, bump up the version
whenever a new field is added to the structure in future. The version
field can be used to find out what fields are valid for the current
version of the structure.
2. Reserve the area of predefined size (say PAGE_SIZE) for this
structure and have unused area as reserved (initialized to zero)
for future field additions.

The advantage of approach 1 over 2 is we don't need to reserve extra space.

Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

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31 changes: 29 additions & 2 deletions arch/powerpc/include/asm/fadump-internal.h
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Expand Up @@ -42,13 +42,38 @@ static inline u64 fadump_str_to_u64(const char *str)

#define FADUMP_CPU_UNKNOWN (~((u32)0))

#define FADUMP_CRASH_INFO_MAGIC fadump_str_to_u64("FADMPINF")
/*
* The introduction of new fields in the fadump crash info header has
* led to a change in the magic key from `FADMPINF` to `FADMPSIG` for
* identifying a kernel crash from an old kernel.
*
* To prevent the need for further changes to the magic number in the
* event of future modifications to the fadump crash info header, a
* version field has been introduced to track the fadump crash info
* header version.
*
* Consider a few points before adding new members to the fadump crash info
* header structure:
*
* - Append new members; avoid adding them in between.
* - Non-primitive members should have a size member as well.
* - For every change in the fadump header, increment the
* fadump header version. This helps the updated kernel decide how to
* handle kernel dumps from older kernels.
*/
#define FADUMP_CRASH_INFO_MAGIC_OLD fadump_str_to_u64("FADMPINF")
#define FADUMP_CRASH_INFO_MAGIC fadump_str_to_u64("FADMPSIG")
#define FADUMP_HEADER_VERSION 1

/* fadump crash info structure */
struct fadump_crash_info_header {
u64 magic_number;
u64 elfcorehdr_addr;
u32 version;
u32 crashing_cpu;
u64 vmcoreinfo_raddr;
u64 vmcoreinfo_size;
u32 pt_regs_sz;
u32 cpu_mask_sz;
struct pt_regs regs;
struct cpumask cpu_mask;
};
Expand Down Expand Up @@ -94,6 +119,8 @@ struct fw_dump {
u64 boot_mem_regs_cnt;

unsigned long fadumphdr_addr;
u64 elfcorehdr_addr;
u64 elfcorehdr_size;
unsigned long cpu_notes_buf_vaddr;
unsigned long cpu_notes_buf_size;

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