[RFC Patch 5/6] slimdump: Capture slimdump for fatal MCE generated crashes

["K.Prasad" <prasad@linux.vnet.ibm.com>]

slimdump: Capture slimdump for fatal MCE generated crashes

System crashes resulting from fatal hardware errors (such as MCE) don't need
all the contents from crashing-kernel's memory. Generate a new 'slimdump' that
retains only essential information while discarding the old memory.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 fs/proc/vmcore.c |  130 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 128 insertions(+), 2 deletions(-)

Index: linux-2.6.slim_kdump/fs/proc/vmcore.c
===================================================================
--- linux-2.6.slim_kdump.orig/fs/proc/vmcore.c
+++ linux-2.6.slim_kdump/fs/proc/vmcore.c
@@ -483,9 +483,60 @@ static void __init set_vmcore_list_offse
 	}
 }
 
+/*
+ * Check if the crash was due to a fatal Memory Check Exception
+ */
+static int is_mce_crash64(void)
+{
+	int i, j, len = 0, rc;
+	Elf64_Ehdr *ehdr_ptr;
+	Elf64_Phdr *phdr_ptr;
+	Elf64_Nhdr *nhdr_ptr;
+
+	ehdr_ptr = (Elf64_Ehdr *)elfcorebuf;
+	phdr_ptr = (Elf64_Phdr *)(elfcorebuf + sizeof(Elf64_Ehdr));
+
+	for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
+		void *notes_section;
+		u64 offset, max_sz;
+		if (phdr_ptr->p_type != PT_NOTE)
+			continue;
+		max_sz = phdr_ptr->p_memsz;
+		offset = phdr_ptr->p_offset;
+		notes_section = kmalloc(max_sz, GFP_KERNEL);
+		if (!notes_section)
+			return -ENOMEM;
+		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
+		if (rc < 0) {
+			kfree(notes_section);
+			return rc;
+		}
+
+		for (j = 0; j < phdr_ptr->p_filesz; j += len) {
+			nhdr_ptr = notes_section + j;
+			if (nhdr_ptr->n_type == NT_MCE)
+			{
+				kfree(notes_section);
+				return 1;
+			}
+			/*
+			 * The elf-64 standard specifies 8-byte alignment while
+			 * append_elf_note function does only 4-byte roundup.
+			 * Hence this code also does a 4-byte roundup.
+			 */
+			len = sizeof(Elf64_Nhdr);
+			len = roundup(len + nhdr_ptr->n_namesz, 4);
+			len = roundup(len + nhdr_ptr->n_descsz, 4);
+		}
+		kfree(notes_section);
+	}
+	return 0;
+}
+
 static int __init parse_crash_elf64_headers(void)
 {
-	int rc=0;
+	int i, rc = 0;
+	Elf64_Phdr *phdr_ptr;
 	Elf64_Ehdr ehdr;
 	u64 addr;
 
@@ -523,6 +574,18 @@ static int __init parse_crash_elf64_head
 		return rc;
 	}
 
+	phdr_ptr = (Elf64_Phdr *)(elfcorebuf + sizeof(Elf64_Ehdr));
+	if (is_mce_crash64() > 0) {
+		/*
+		 * If crash is due to Machine Check exception, don't populate
+		 * sections other than elf-notes. Mark their sizes as zero.
+		 */
+		for (i = 0; i < ehdr.e_phnum; i++, phdr_ptr++) {
+			if (phdr_ptr->p_type != PT_NOTE)
+				phdr_ptr->p_memsz = phdr_ptr->p_filesz = 0;
+		}
+	}
+
 	/* Merge all PT_NOTE headers into one. */
 	rc = merge_note_headers_elf64(elfcorebuf, &elfcorebuf_sz, &vmcore_list);
 	if (rc) {
@@ -539,9 +602,60 @@ static int __init parse_crash_elf64_head
 	return 0;
 }
 
+/*
+ * Check if the crash was due to a fatal Memory Check Exception
+ */
+static int is_mce_crash32(void)
+{
+	int i, j, len = 0, rc;
+	Elf32_Ehdr *ehdr_ptr;
+	Elf32_Phdr *phdr_ptr;
+	Elf32_Nhdr *nhdr_ptr;
+
+	ehdr_ptr = (Elf32_Ehdr *)elfcorebuf;
+	phdr_ptr = (Elf32_Phdr *)(elfcorebuf + sizeof(Elf32_Ehdr));
+
+	for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
+		void *notes_section;
+		u64 offset, max_sz;
+		if (phdr_ptr->p_type != PT_NOTE)
+			continue;
+		max_sz = phdr_ptr->p_memsz;
+		offset = phdr_ptr->p_offset;
+		notes_section = kmalloc(max_sz, GFP_KERNEL);
+		if (!notes_section)
+			return -ENOMEM;
+		rc = read_from_oldmem(notes_section, max_sz, &offset, 0);
+		if (rc < 0) {
+			kfree(notes_section);
+			return rc;
+		}
+
+		for (j = 0; j < phdr_ptr->p_filesz; j += len) {
+			nhdr_ptr = notes_section + j;
+			if (nhdr_ptr->n_type == NT_MCE)
+			{
+				kfree(notes_section);
+				return 1;
+			}
+			/*
+			 * The elf-64 standard specifies 8-byte alignment while
+			 * append_elf_note function does only 4-byte roundup.
+			 * Hence this code also does a 4-byte roundup.
+			 */
+			len = sizeof(Elf64_Nhdr);
+			len = roundup(len + nhdr_ptr->n_namesz, 4);
+			len = roundup(len + nhdr_ptr->n_descsz, 4);
+		}
+		kfree(notes_section);
+	}
+	return 0;
+}
+
 static int __init parse_crash_elf32_headers(void)
 {
-	int rc=0;
+	int i, rc = 0;
+	Elf32_Phdr *phdr_ptr;
 	Elf32_Ehdr ehdr;
 	u64 addr;
 
@@ -579,6 +693,18 @@ static int __init parse_crash_elf32_head
 		return rc;
 	}
 
+	phdr_ptr = (Elf32_Phdr *)(elfcorebuf + sizeof(Elf32_Ehdr));
+	if (is_mce_crash32() > 0) {
+		/*
+		 * If crash is due to Machine Check exception, don't populate
+		 * sections other than elf-notes. Mark their sizes as zero.
+		 */
+		for (i = 0; i < ehdr.e_phnum; i++, phdr_ptr++) {
+			if (phdr_ptr->p_type != PT_NOTE)
+				phdr_ptr->p_memsz = phdr_ptr->p_filesz = 0;
+		}
+	}
+
 	/* Merge all PT_NOTE headers into one. */
 	rc = merge_note_headers_elf32(elfcorebuf, &elfcorebuf_sz, &vmcore_list);
 	if (rc) {