From patchwork series 395410

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=395410

Author: Fox Snowpatch

Documentation/ABI/testing/sysfs-kernel-fadump

@@ -38,3 +38,14 @@ Contact:	[email protected]
 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:		Feb 2024
+Contact:	[email protected]
+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

Documentation/arch/powerpc/firmware-assisted-dump.rst

@@ -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
@@ -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
@@ -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
 
 
@@ -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 <[email protected]>
 

arch/powerpc/include/asm/fadump-internal.h

@@ -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;
 };
@@ -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;