arch/i386/kernel/alternative.c

#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/list.h>
#include <asm/alternative.h>
#include <asm/sections.h>

#define DEBUG 0
#if DEBUG
# define DPRINTK(fmt, args...) printk(fmt, args)
#else
# define DPRINTK(fmt, args...)
#endif

/* Use inline assembly to define this because the nops are defined
   as inline assembly strings in the include files and we cannot
   get them easily into strings. */
asm("\t.data\nintelnops: "
	GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 GENERIC_NOP6
	GENERIC_NOP7 GENERIC_NOP8);
asm("\t.data\nk8nops: "
	K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
	K8_NOP7 K8_NOP8);
asm("\t.data\nk7nops: "
	K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
	K7_NOP7 K7_NOP8);

extern unsigned char intelnops[], k8nops[], k7nops[];
static unsigned char *intel_nops[ASM_NOP_MAX+1] = {
	NULL,
	intelnops,
	intelnops + 1,
	intelnops + 1 + 2,
	intelnops + 1 + 2 + 3,
	intelnops + 1 + 2 + 3 + 4,
	intelnops + 1 + 2 + 3 + 4 + 5,
	intelnops + 1 + 2 + 3 + 4 + 5 + 6,
	intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
static unsigned char *k8_nops[ASM_NOP_MAX+1] = {
	NULL,
	k8nops,
	k8nops + 1,
	k8nops + 1 + 2,
	k8nops + 1 + 2 + 3,
	k8nops + 1 + 2 + 3 + 4,
	k8nops + 1 + 2 + 3 + 4 + 5,
	k8nops + 1 + 2 + 3 + 4 + 5 + 6,
	k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
static unsigned char *k7_nops[ASM_NOP_MAX+1] = {
	NULL,
	k7nops,
	k7nops + 1,
	k7nops + 1 + 2,
	k7nops + 1 + 2 + 3,
	k7nops + 1 + 2 + 3 + 4,
	k7nops + 1 + 2 + 3 + 4 + 5,
	k7nops + 1 + 2 + 3 + 4 + 5 + 6,
	k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
static struct nop {
	int cpuid;
	unsigned char **noptable;
} noptypes[] = {
	{ X86_FEATURE_K8, k8_nops },
	{ X86_FEATURE_K7, k7_nops },
	{ -1, NULL }
};


extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern struct alt_instr __smp_alt_instructions[], __smp_alt_instructions_end[];
extern u8 *__smp_locks[], *__smp_locks_end[];

extern u8 __smp_alt_begin[], __smp_alt_end[];


static unsigned char** find_nop_table(void)
{
	unsigned char **noptable = intel_nops;
	int i;

	for (i = 0; noptypes[i].cpuid >= 0; i++) {
		if (boot_cpu_has(noptypes[i].cpuid)) {
			noptable = noptypes[i].noptable;
			break;
		}
	}
	return noptable;
}

/* Replace instructions with better alternatives for this CPU type.
   This runs before SMP is initialized to avoid SMP problems with
   self modifying code. This implies that assymetric systems where
   APs have less capabilities than the boot processor are not handled.
   Tough. Make sure you disable such features by hand. */

void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
{
	unsigned char **noptable = find_nop_table();
	struct alt_instr *a;
	int diff, i, k;

	DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
	for (a = start; a < end; a++) {
		BUG_ON(a->replacementlen > a->instrlen);
		if (!boot_cpu_has(a->cpuid))
			continue;
		memcpy(a->instr, a->replacement, a->replacementlen);
		diff = a->instrlen - a->replacementlen;
		/* Pad the rest with nops */
		for (i = a->replacementlen; diff > 0; diff -= k, i += k) {
			k = diff;
			if (k > ASM_NOP_MAX)
				k = ASM_NOP_MAX;
			memcpy(a->instr + i, noptable[k], k);
		}
	}
}

static void alternatives_smp_save(struct alt_instr *start, struct alt_instr *end)
{
	struct alt_instr *a;

	DPRINTK("%s: alt table %p-%p\n", __FUNCTION__, start, end);
	for (a = start; a < end; a++) {
		memcpy(a->replacement + a->replacementlen,
		       a->instr,
		       a->instrlen);
	}
}

static void alternatives_smp_apply(struct alt_instr *start, struct alt_instr *end)
{
	struct alt_instr *a;

	for (a = start; a < end; a++) {
		memcpy(a->instr,
		       a->replacement + a->replacementlen,
		       a->instrlen);
	}
}

static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	u8 **ptr;

	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		**ptr = 0xf0; /* lock prefix */
	};
}

static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	unsigned char **noptable = find_nop_table();
	u8 **ptr;

	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		**ptr = noptable[1][0];
	};
}

struct smp_alt_module {
	/* what is this ??? */
	struct module	*mod;
	char		*name;

	/* ptrs to lock prefixes */
	u8		**locks;
	u8		**locks_end;

	/* .text segment, needed to avoid patching init code ;) */
	u8		*text;
	u8		*text_end;

	struct list_head next;
};
static LIST_HEAD(smp_alt_modules);
static DEFINE_SPINLOCK(smp_alt);

static int smp_alt_once = 0;
static int __init bootonly(char *str)
{
	smp_alt_once = 1;
	return 1;
}
__setup("smp-alt-boot", bootonly);

void alternatives_smp_module_add(struct module *mod, char *name,
				 void *locks, void *locks_end,
				 void *text,  void *text_end)
{
	struct smp_alt_module *smp;
	unsigned long flags;

	if (smp_alt_once) {
		if (boot_cpu_has(X86_FEATURE_UP))
			alternatives_smp_unlock(locks, locks_end,
						text, text_end);
		return;
	}

	smp = kzalloc(sizeof(*smp), GFP_KERNEL);
	if (NULL == smp)
		return; /* we'll run the (safe but slow) SMP code then ... */

	smp->mod	= mod;
	smp->name	= name;
	smp->locks	= locks;
	smp->locks_end	= locks_end;
	smp->text	= text;
	smp->text_end	= text_end;
	DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
		__FUNCTION__, smp->locks, smp->locks_end,
		smp->text, smp->text_end, smp->name);

	spin_lock_irqsave(&smp_alt, flags);
	list_add_tail(&smp->next, &smp_alt_modules);
	if (boot_cpu_has(X86_FEATURE_UP))
		alternatives_smp_unlock(smp->locks, smp->locks_end,
					smp->text, smp->text_end);
	spin_unlock_irqrestore(&smp_alt, flags);
}

void alternatives_smp_module_del(struct module *mod)
{
	struct smp_alt_module *item;
	unsigned long flags;

	if (smp_alt_once)
		return;

	spin_lock_irqsave(&smp_alt, flags);
	list_for_each_entry(item, &smp_alt_modules, next) {
		if (mod != item->mod)
			continue;
		list_del(&item->next);
		spin_unlock_irqrestore(&smp_alt, flags);
		DPRINTK("%s: %s\n", __FUNCTION__, item->name);
		kfree(item);
		return;
	}
	spin_unlock_irqrestore(&smp_alt, flags);
}

void alternatives_smp_switch(int smp)
{
	struct smp_alt_module *mod;
	unsigned long flags;

	if (smp_alt_once)
		return;
	BUG_ON(!smp && (num_online_cpus() > 1));

	spin_lock_irqsave(&smp_alt, flags);
	if (smp) {
		printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
		clear_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
		clear_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
		alternatives_smp_apply(__smp_alt_instructions,
				       __smp_alt_instructions_end);
		list_for_each_entry(mod, &smp_alt_modules, next)
			alternatives_smp_lock(mod->locks, mod->locks_end,
					      mod->text, mod->text_end);
	} else {
		printk(KERN_INFO "SMP alternatives: switching to UP code\n");
		set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
		set_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
		apply_alternatives(__smp_alt_instructions,
				   __smp_alt_instructions_end);
		list_for_each_entry(mod, &smp_alt_modules, next)
			alternatives_smp_unlock(mod->locks, mod->locks_end,
						mod->text, mod->text_end);
	}
	spin_unlock_irqrestore(&smp_alt, flags);
}

void __init alternative_instructions(void)
{
	apply_alternatives(__alt_instructions, __alt_instructions_end);

	/* switch to patch-once-at-boottime-only mode and free the
	 * tables in case we know the number of CPUs will never ever
	 * change */
#ifdef CONFIG_HOTPLUG_CPU
	if (num_possible_cpus() < 2)
		smp_alt_once = 1;
#else
	smp_alt_once = 1;
#endif

	if (smp_alt_once) {
		if (1 == num_possible_cpus()) {
			printk(KERN_INFO "SMP alternatives: switching to UP code\n");
			set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
			set_bit(X86_FEATURE_UP, cpu_data[0].x86_capability);
			apply_alternatives(__smp_alt_instructions,
					   __smp_alt_instructions_end);
			alternatives_smp_unlock(__smp_locks, __smp_locks_end,
						_text, _etext);
		}
		free_init_pages("SMP alternatives",
				(unsigned long)__smp_alt_begin,
				(unsigned long)__smp_alt_end);
	} else {
		alternatives_smp_save(__smp_alt_instructions,
				      __smp_alt_instructions_end);
		alternatives_smp_module_add(NULL, "core kernel",
					    __smp_locks, __smp_locks_end,
					    _text, _etext);
		alternatives_smp_switch(0);
	}
}