kdump: Initialize vmcoreinfo note at startup

Hello Andrew,

Another common code patch that we would like to have upstream is the vmcoreinfo note initialization at Linux startup time. We need that for our traditional stand-alone and hypervisor dump tools.

[1] kdump: Initialize vmcoreinfo note at startup
[2] s390: Export vmcoreinfo note

I already have discussed this with Vivek and he has acked the common code patch [1].

Do you agree that Martin sends these patches together with the kdump page table patches (see https://lkml.org/lkml/2011/9/15/55) in the next merge window?

Michael

From: Michael Holzheu <[email protected]>

Currently the vmcoreinfo note is only initialized in case of kdump. On s390 it is possible to create kernel dumps with other dump mechanisms than kdump (e.g. via hypervisor dump or stand-alone dump tools). For those dumps it would also be desirable to include the vmcoreinfo data. To accomplish this, with this patch the vmcoreinfo ELF note is always initialized, not only in case of a (kdump) crash. On s390 we will add an ABI defined pointer at a well known address to vmcoreinfo so that dump analysis tools are able to find this information.

In particular on s390 we have a tool named zgetdump. With this tool it is possible to convert dump formats on the fly using fuse. E.g. you can mount a s390 stand-alone dump as ELF dump. When this is done, the tool finds the vmcoreinfo in the stand-alone dump via the well known ABI defined address and it creates the respective VMCOREINFO ELF note in the output ELF dump. This then can be used e.g. by makedumpfile for dump filtering. No more need for a vmlinux file with debug information.

So this will look like the following:

$ zgetdump --mount standalone.dump -f elf /mnt
$ ls /mnt
  dump.elf
$ readelf -n /mnt/dump.elf
$ ...
  VMCOREINFO            0x00000474      Unknown note type: (0x00000000)
$ makedumpfile -c -d 31 /mnt/dump.elf dump.kdump

---
 kernel/kexec.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

@@ -1392,24 +1392,23 @@ int __init parse_crashkernel(char 		 *cm
 }
 
 
-
-void crash_save_vmcoreinfo(void)
+static void update_vmcoreinfo_note(void)
 {
-	u32 *buf;
+	u32 *buf = (u32 *) vmcoreinfo_note;
 
 	if (!vmcoreinfo_size)
 		return;
-
-	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
-
-	buf = (u32 *)vmcoreinfo_note;
-
 	buf = append_elf_note(buf, VMCOREINFO_NOTE_NAME, 0, vmcoreinfo_data,
 			      vmcoreinfo_size);
-
 	final_note(buf);
 }
 
+void crash_save_vmcoreinfo(void)
+{
+	vmcoreinfo_append_str("CRASHTIME=%ld", get_seconds());
+	update_vmcoreinfo_note();
+}
+
 void vmcoreinfo_append_str(const char *fmt, ...)
 {
 	va_list args;

@@ -1495,6 +1494,7 @@ static int __init crash_save_vmcoreinfo_
 	VMCOREINFO_NUMBER(PG_swapcache);
 
 	arch_crash_save_vmcoreinfo();
+	update_vmcoreinfo_note();
 
 	return 0;
 }

Hello Andrew,

[snip]

Correct. I removed the cast (with the blank :), thanks!

Michael

From: Michael Holzheu <[email protected]>

This patch defines for s390 an ABI defined pointer to the vmcoreinfo note at a well known address. With this patch tools are able to find this information in dumps created by stand-alone or hypervisor dump tools.

---
 arch/s390/include/asm/lowcore.h |    3 ++-
 arch/s390/kernel/setup.c        |    8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

@@ -287,7 +287,8 @@ struct _lowcore {
 	 */
 	__u64	ipib;				/* 0x0e00 */
 	__u32	ipib_checksum;			/* 0x0e08 */
-	__u8	pad_0x0e0c[0x0f00-0x0e0c];	/* 0x0e0c */
+	__u64	vmcore_info;			/* 0x0e0c */
+	__u8	pad_0x0e14[0x0f00-0x0e14];	/* 0x0e14 */
 
 	/* Extended facility list */
 	__u64	stfle_fac_list[32];		/* 0x0f00 */

@@ -559,6 +559,13 @@ static void __init setup_restart_psw(voi
 	copy_to_absolute_zero(&S390_lowcore.restart_psw, &psw, sizeof(psw));
 }
 
+static void __init setup_vmcoreinfo(void)
+{
+	unsigned long ptr = paddr_vmcoreinfo_note();
+
+	copy_to_absolute_zero(&S390_lowcore.vmcore_info, &ptr, sizeof(ptr));
+}
+
 #ifdef CONFIG_CRASH_DUMP
 
 /*

@@ -1019,6 +1026,7 @@ setup_arch(char **cmdline_p)
 	reserve_crashkernel();
 	setup_memory();
 	setup_resources();
+	setup_vmcoreinfo();
 	setup_restart_psw();
 	setup_lowcore();
 

Sounds good to me, thanks.