[-next,2/2,RFC] x86: Saveoops: Reserve low memory and register code

diff --git a/arch/x86/kernel/saveoops.c b/arch/x86/kernel/saveoops.c
new file mode 100644
index 0000000..f48fc0a
--- /dev/null
+++ b/arch/x86/kernel/saveoops.c
@@ -0,0 +1,219 @@ 
+/* PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE */
+
+/*
+ * SAVEOOPS -- Save kernel log buffer to disk upon panic()
+ *
+ * To safely access disk in situations like very early boot or where the
+ * disk access code itself is buggy, we use BIOS INT13h extended services.
+ * To access such services, switch to 8086 real-mode first.
+ */
+
+#include <linux/kernel.h>
+#include <linux/compiler.h>
+#include <linux/log2.h>
+#include <linux/time.h>
+#include <linux/kmsg_dump.h>
+#include <linux/memblock.h>
+#include <linux/sched.h>
+
+#include <asm/page.h>
+#include <asm/pgtable.h>
+#include <asm/tlbflush.h>
+#include <asm/saveoops.h>
+
+/*
+ * We can only access the first MByte in real mode, thus allocate
+ * low-memory areas for the ring buffer, and rmode code and stack.
+ */
+static phys_addr_t ring_buf;
+static phys_addr_t code_buf;
+static phys_addr_t rmode_stack;
+
+/*
+ * Below 1-Mbyte pointer to lmode->rmode switch code.
+ */
+static void (* __noreturn rmode_switch)(phys_addr_t code_buf,
+					phys_addr_t ring_buf,
+					phys_addr_t rmode_stack,
+					uint64_t disk_lba,
+					uint64_t ring_buf_len);
+
+/*
+ * Absolute LBA address where the log will be saved on disk.
+ */
+static uint64_t disk_lba = CONFIG_SAVEOOPS_DISK_LBA;
+
+/*
+ * Extended BIOS services write to disk in units of 512-byte sectors.
+ * Thus, always align the ring buffer size on a 512-byte boundary.
+ */
+#define RMODE_SEGMENT_LIMIT	0x10000UL
+#define RING_SIZE		(60UL * 1024)
+#define SAVEOOPS_HEADER		"*SAVEOOPS-WRITTEN KERNEL LOG*"
+
+/*
+ * Page tables to identity map the first 2 Mbytes.
+ */
+static __aligned(PAGE_SIZE) pud_t ident_level3[PTRS_PER_PUD];
+static __aligned(PAGE_SIZE) pmd_t ident_level2[PTRS_PER_PMD];
+
+/*
+ * The lmode->rmode switching code needs to run from an identity page
+ * since it disables paging.
+ */
+static void build_identity_mappings(void)
+{
+	pgd_t *pgde;
+	pud_t *pude;
+	pmd_t *pmde;
+
+	pmde = ident_level2;
+	set_pmd(pmde, __pmd(0 + __PAGE_KERNEL_IDENT_LARGE_EXEC));
+
+	pude = ident_level3;
+	set_pud(pude, __pud(__pa(ident_level2) + _KERNPG_TABLE));
+
+	pgde = init_level4_pgt;
+	set_pgd(pgde, __pgd(__pa(ident_level3) + _KERNPG_TABLE));
+
+	__flush_tlb_all();
+}
+
+/*
+ * XXX: Our use of kmsg_dump interface is invalid. We completely halt the
+ *	machine when getting called; this means:
+ *	- other registered loggers won't have a chance to read the ring
+ *	- other CPU cores might also be accessing the disk, racing with
+ *	  BIOS code that will do the same.
+ *
+ *	Such interface is now used to get things going. A new interface
+ *	satisfying our special requirements needs to be created. A
+ *	solution is to do an rmode->lmode switch after writing to disk.
+ */
+static void saveoops_do_dump(struct kmsg_dumper *dumper,
+			     enum kmsg_dump_reason reason,
+			     const char *s1, unsigned long l1,
+			     const char *s2, unsigned long l2)
+{
+	unsigned long l1_cpy, l2_cpy, s1_start, s2_start;
+	struct timeval timestamp;
+	char *buf, *buf_orig;
+	int hdr_size;
+
+	if (reason != KMSG_DUMP_PANIC)
+		return;
+
+	do_gettimeofday(&timestamp);
+
+	buf = __va(ring_buf);
+	buf_orig = buf;
+	memset(buf, '\0', RING_SIZE);
+	buf += sprintf(buf, "%s\n", SAVEOOPS_HEADER);
+	buf += sprintf(buf, "%lu.%lu\n", timestamp.tv_sec, timestamp.tv_usec);
+
+	hdr_size = buf - buf_orig;
+	l2_cpy = min(l2, RING_SIZE - hdr_size);
+	l1_cpy = min(l1, RING_SIZE - hdr_size - l2_cpy);
+
+	s2_start = l2 - l2_cpy;
+	s1_start = l1 - l1_cpy;
+	memcpy(buf, s1 + s1_start, l1_cpy);
+	memcpy(buf + l1_cpy, s2 + s2_start, l2_cpy);
+
+	printk(KERN_EMERG "Saveoops: Saving kernel log to boot disk LBA "
+	       "address %llu\n", disk_lba);
+
+	local_irq_disable();
+	build_identity_mappings();
+	rmode_switch(code_buf, ring_buf, rmode_stack, disk_lba, RING_SIZE >> 9);
+}
+
+static struct kmsg_dumper saveoops_dumper = {
+	.dump = saveoops_do_dump,
+};
+
+/*
+ * Real-mode switch code start and end markers.
+ * @pmode16: 16-bit protected mode entry point; 8086-segments base.
+ */
+extern const char saveoops_start[];
+extern const char saveoops_end[];
+extern const char pmode16[];
+
+/*
+ * Simplify real mode segmented-addressing calculations
+ */
+#define RMODE_DATA_ALIGN	16
+
+void __init saveoops_init(void)
+{
+	unsigned int code_size, code_align;
+	int res;
+
+	if (disk_lba == -1) {
+		printk(KERN_INFO "Saveoops: No disk LBA given; will not save "
+		       "kernel log to disk upon panic.\n");
+		return;
+	}
+
+	BUILD_BUG_ON(!IS_ALIGNED(RING_SIZE, 512));
+	BUILD_BUG_ON(RING_SIZE > RMODE_SEGMENT_LIMIT);
+	BUILD_BUG_ON(RMODE_STACK_LEN > RMODE_SEGMENT_LIMIT);
+	BUG_ON((saveoops_end - pmode16) > RMODE_SEGMENT_LIMIT);
+
+	ring_buf = memblock_find_in_range(0, 1<<20, RING_SIZE, RMODE_DATA_ALIGN);
+	if (ring_buf == MEMBLOCK_ERROR) {
+		printk(KERN_ERR "Saveoops: requesting a low-memory region "
+		       "for ring buffer failed\n");
+		return;
+	}
+	memblock_x86_reserve_range(ring_buf, ring_buf + RING_SIZE,
+				   "SAVEOOPS ringbuf");
+	printk(KERN_INFO "Saveoops: Acquired [0x%llx-0x%llx] for the ring "
+	       "buffer\n", ring_buf, ring_buf + RING_SIZE);
+
+	/* The pmode->rmode switch code “MUST” be in a single page */
+	code_size = saveoops_end - saveoops_start;
+	code_align = roundup_pow_of_two(code_size);
+	code_buf = memblock_find_in_range(0, 1<<20, code_size, code_align);
+	if (code_buf == MEMBLOCK_ERROR) {
+		printk(KERN_ERR "Saveoops: requesting a low-memory region "
+		       "for mode-switching code failed\n");
+		goto fail3;
+	}
+	memblock_x86_reserve_range(code_buf, code_buf + code_size,
+				   "SAVEOOPS codebuf");
+	printk(KERN_INFO "Saveoops: Acquired [0x%llx-0x%llx] for rmode-switch "
+	       "code\n", code_buf, code_buf + code_size);
+
+	rmode_stack = memblock_find_in_range(0, 1<<20, RMODE_STACK_LEN,
+					     RMODE_DATA_ALIGN);
+	if (rmode_stack == MEMBLOCK_ERROR) {
+		printk(KERN_ERR "Saveoops: requesting a low-memory region "
+		       "for real-mode stack failed\n");
+		goto fail2;
+	}
+	memblock_x86_reserve_range(rmode_stack, rmode_stack + RMODE_STACK_LEN,
+				   "SAVEOOPS r-stack");
+	printk(KERN_INFO "Saveoops: Acquired [0x%llx-0x%llx] for rmode stack\n",
+	       rmode_stack, rmode_stack + RMODE_STACK_LEN);
+
+	res = kmsg_dump_register(&saveoops_dumper);
+	if (res) {
+		printk(KERN_ERR "Saveoops: registering kmsg dumper failed");
+		goto fail1;
+	}
+
+	memcpy(__va(code_buf), saveoops_start, code_size);
+	rmode_switch = (void *)code_buf;
+	return;
+
+fail1:
+	memblock_x86_free_range(rmode_stack, rmode_stack + RMODE_STACK_LEN);
+fail2:
+	memblock_x86_free_range(code_buf, code_buf + code_size);
+fail3:
+	memblock_x86_free_range(ring_buf, ring_buf + RING_SIZE);
+}
+
+/* PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE - PROTOTYPE */
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d3cfe26..3686df8 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -50,6 +50,9 @@ 
 #include <asm/pci-direct.h>
 #include <linux/init_ohci1394_dma.h>
 #include <linux/kvm_para.h>
+#ifdef CONFIG_SAVEOOPS
+#include <asm/saveoops.h>
+#endif
 
 #include <linux/errno.h>
 #include <linux/kernel.h>
@@ -925,6 +928,12 @@  void __init setup_arch(char **cmdline_p)
 	memblock.current_limit = get_max_mapped();
 	memblock_x86_fill();
 
+#ifdef CONFIG_SAVEOOPS
+	/* Initialize Saveoops at the earliest point possible: memblock
+	 * find_in_range is used here to reserve low-memory areas */
+	saveoops_init();
+#endif
+
 	/* preallocate 4k for mptable mpc */
 	early_reserve_e820_mpc_new();

diff --git a/arch/x86/include/asm/saveoops.h b/arch/x86/include/asm/saveoops.h
new file mode 100644
index 0000000..d81e840
--- /dev/null
+++ b/arch/x86/include/asm/saveoops.h
@@ -0,0 +1,15 @@ 
+#ifndef _SAVEOOPS_H
+#define _SAVEOOPS_H
+
+/*
+ * Definitions shared between Saveoops C and assembly code.
+ */
+
+#define RMODE_STACK_LEN		0x1000	/* Arbitrary */
+
+#ifndef __ASSEMBLY__
+
+void __init saveoops_init(void);
+
+#endif /* !__ASSEMBLY__ */
+#endif /* _SAVEOOPS_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 34244b2..9a097f2 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -121,4 +121,7 @@  ifeq ($(CONFIG_X86_64),y)
 
 	obj-$(CONFIG_PCI_MMCONFIG)	+= mmconf-fam10h_64.o
 	obj-y				+= vsmp_64.o
+
+	obj-$(CONFIG_SAVEOOPS)		+= saveoops.o
+	obj-$(CONFIG_SAVEOOPS)		+= saveoops-rmode.o
 endif
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4a78f8c..b994791 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -231,6 +231,21 @@  config BOOTPARAM_HUNG_TASK_PANIC
 
 	  Say N if unsure.
 
+config SAVEOOPS
+	bool "Save kernel panics to disk using BIOS"
+	depends on X86_64
+	---help---
+	  <TO-BE-ADDED>
+
+config SAVEOOPS_DISK_LBA
+       int "Boot disk LBA offset to save panic to"
+       default -1
+       depends on SAVEOOPS
+       ---help---
+	 Use this boot disk LBA address to save the kernel log.
+	 To find a partition LBA address use: $fdisk -ul
+	 [VERY DANGEROUS] <FURTHER-INFO-TO-BE-ADDED>
+
 config BOOTPARAM_HUNG_TASK_PANIC_VALUE
 	int
 	depends on DETECT_HUNG_TASK