pgtable.c

/*
 *    Copyright IBM Corp. 2007,2009
 *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/smp.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include <linux/quicklist.h>
#include <linux/rcupdate.h>

#include <asm/system.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>

struct rcu_table_freelist {
	struct rcu_head rcu;
	struct mm_struct *mm;
	unsigned int pgt_index;
	unsigned int crst_index;
	unsigned long *table[0];
};

#define RCU_FREELIST_SIZE \
	((PAGE_SIZE - sizeof(struct rcu_table_freelist)) \
	  / sizeof(unsigned long))

DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
static DEFINE_PER_CPU(struct rcu_table_freelist *, rcu_table_freelist);

static void __page_table_free(struct mm_struct *mm, unsigned long *table);
static void __crst_table_free(struct mm_struct *mm, unsigned long *table);

static struct rcu_table_freelist *rcu_table_freelist_get(struct mm_struct *mm)
{
	struct rcu_table_freelist **batchp = &__get_cpu_var(rcu_table_freelist);
	struct rcu_table_freelist *batch = *batchp;

	if (batch)
		return batch;
	batch = (struct rcu_table_freelist *) __get_free_page(GFP_ATOMIC);
	if (batch) {
		batch->mm = mm;
		batch->pgt_index = 0;
		batch->crst_index = RCU_FREELIST_SIZE;
		*batchp = batch;
	}
	return batch;
}

static void rcu_table_freelist_callback(struct rcu_head *head)
{
	struct rcu_table_freelist *batch =
		container_of(head, struct rcu_table_freelist, rcu);

	while (batch->pgt_index > 0)
		__page_table_free(batch->mm, batch->table[--batch->pgt_index]);
	while (batch->crst_index < RCU_FREELIST_SIZE)
		__crst_table_free(batch->mm, batch->table[batch->crst_index++]);
	free_page((unsigned long) batch);
}

void rcu_table_freelist_finish(void)
{
	struct rcu_table_freelist *batch = __get_cpu_var(rcu_table_freelist);

	if (!batch)
		return;
	call_rcu(&batch->rcu, rcu_table_freelist_callback);
	__get_cpu_var(rcu_table_freelist) = NULL;
}

static void smp_sync(void *arg)
{
}

#ifndef CONFIG_64BIT
#define ALLOC_ORDER	1
#define TABLES_PER_PAGE	4
#define FRAG_MASK	15UL
#define SECOND_HALVES	10UL

void clear_table_pgstes(unsigned long *table)
{
	clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
	memset(table + 256, 0, PAGE_SIZE/4);
	clear_table(table + 512, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
	memset(table + 768, 0, PAGE_SIZE/4);
}

#else
#define ALLOC_ORDER	2
#define TABLES_PER_PAGE	2
#define FRAG_MASK	3UL
#define SECOND_HALVES	2UL

void clear_table_pgstes(unsigned long *table)
{
	clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/2);
	memset(table + 256, 0, PAGE_SIZE/2);
}

#endif

unsigned long VMALLOC_START = VMALLOC_END - VMALLOC_SIZE;
EXPORT_SYMBOL(VMALLOC_START);

static int __init parse_vmalloc(char *arg)
{
	if (!arg)
		return -EINVAL;
	VMALLOC_START = (VMALLOC_END - memparse(arg, &arg)) & PAGE_MASK;
	return 0;
}
early_param("vmalloc", parse_vmalloc);

unsigned long *crst_table_alloc(struct mm_struct *mm, int noexec)
{
	struct page *page = alloc_pages(GFP_KERNEL, ALLOC_ORDER);

	if (!page)
		return NULL;
	page->index = 0;
	if (noexec) {
		struct page *shadow = alloc_pages(GFP_KERNEL, ALLOC_ORDER);
		if (!shadow) {
			__free_pages(page, ALLOC_ORDER);
			return NULL;
		}
		page->index = page_to_phys(shadow);
	}
	spin_lock_bh(&mm->context.list_lock);
	list_add(&page->lru, &mm->context.crst_list);
	spin_unlock_bh(&mm->context.list_lock);
	return (unsigned long *) page_to_phys(page);
}

static void __crst_table_free(struct mm_struct *mm, unsigned long *table)
{
	unsigned long *shadow = get_shadow_table(table);

	if (shadow)
		free_pages((unsigned long) shadow, ALLOC_ORDER);
	free_pages((unsigned long) table, ALLOC_ORDER);
}

void crst_table_free(struct mm_struct *mm, unsigned long *table)
{
	struct page *page = virt_to_page(table);

	spin_lock_bh(&mm->context.list_lock);
	list_del(&page->lru);
	spin_unlock_bh(&mm->context.list_lock);
	__crst_table_free(mm, table);
}

void crst_table_free_rcu(struct mm_struct *mm, unsigned long *table)
{
	struct rcu_table_freelist *batch;
	struct page *page = virt_to_page(table);

	spin_lock_bh(&mm->context.list_lock);
	list_del(&page->lru);
	spin_unlock_bh(&mm->context.list_lock);
	if (atomic_read(&mm->mm_users) < 2 &&
	    cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
		__crst_table_free(mm, table);
		return;
	}
	batch = rcu_table_freelist_get(mm);
	if (!batch) {
		smp_call_function(smp_sync, NULL, 1);
		__crst_table_free(mm, table);
		return;
	}
	batch->table[--batch->crst_index] = table;
	if (batch->pgt_index >= batch->crst_index)
		rcu_table_freelist_finish();
}

#ifdef CONFIG_64BIT
int crst_table_upgrade(struct mm_struct *mm, unsigned long limit)
{
	unsigned long *table, *pgd;
	unsigned long entry;

	BUG_ON(limit > (1UL << 53));
repeat:
	table = crst_table_alloc(mm, mm->context.noexec);
	if (!table)
		return -ENOMEM;
	spin_lock_bh(&mm->page_table_lock);
	if (mm->context.asce_limit < limit) {
		pgd = (unsigned long *) mm->pgd;
		if (mm->context.asce_limit <= (1UL << 31)) {
			entry = _REGION3_ENTRY_EMPTY;
			mm->context.asce_limit = 1UL << 42;
			mm->context.asce_bits = _ASCE_TABLE_LENGTH |
						_ASCE_USER_BITS |
						_ASCE_TYPE_REGION3;
		} else {
			entry = _REGION2_ENTRY_EMPTY;
			mm->context.asce_limit = 1UL << 53;
			mm->context.asce_bits = _ASCE_TABLE_LENGTH |
						_ASCE_USER_BITS |
						_ASCE_TYPE_REGION2;
		}
		crst_table_init(table, entry);
		pgd_populate(mm, (pgd_t *) table, (pud_t *) pgd);
		mm->pgd = (pgd_t *) table;
		mm->task_size = mm->context.asce_limit;
		table = NULL;
	}
	spin_unlock_bh(&mm->page_table_lock);
	if (table)
		crst_table_free(mm, table);
	if (mm->context.asce_limit < limit)
		goto repeat;
	update_mm(mm, current);
	return 0;
}

void crst_table_downgrade(struct mm_struct *mm, unsigned long limit)
{
	pgd_t *pgd;

	if (mm->context.asce_limit <= limit)
		return;
	__tlb_flush_mm(mm);
	while (mm->context.asce_limit > limit) {
		pgd = mm->pgd;
		switch (pgd_val(*pgd) & _REGION_ENTRY_TYPE_MASK) {
		case _REGION_ENTRY_TYPE_R2:
			mm->context.asce_limit = 1UL << 42;
			mm->context.asce_bits = _ASCE_TABLE_LENGTH |
						_ASCE_USER_BITS |
						_ASCE_TYPE_REGION3;
			break;
		case _REGION_ENTRY_TYPE_R3:
			mm->context.asce_limit = 1UL << 31;
			mm->context.asce_bits = _ASCE_TABLE_LENGTH |
						_ASCE_USER_BITS |
						_ASCE_TYPE_SEGMENT;
			break;
		default:
			BUG();
		}
		mm->pgd = (pgd_t *) (pgd_val(*pgd) & _REGION_ENTRY_ORIGIN);
		mm->task_size = mm->context.asce_limit;
		crst_table_free(mm, (unsigned long *) pgd);
	}
	update_mm(mm, current);
}
#endif

/*
 * page table entry allocation/free routines.
 */
unsigned long *page_table_alloc(struct mm_struct *mm)
{
	struct page *page;
	unsigned long *table;
	unsigned long bits;

	bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
	spin_lock_bh(&mm->context.list_lock);
	page = NULL;
	if (!list_empty(&mm->context.pgtable_list)) {
		page = list_first_entry(&mm->context.pgtable_list,
					struct page, lru);
		if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
			page = NULL;
	}
	if (!page) {
		spin_unlock_bh(&mm->context.list_lock);
		page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
		if (!page)
			return NULL;
		pgtable_page_ctor(page);
		page->flags &= ~FRAG_MASK;
		table = (unsigned long *) page_to_phys(page);
		if (mm->context.has_pgste)
			clear_table_pgstes(table);
		else
			clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
		spin_lock_bh(&mm->context.list_lock);
		list_add(&page->lru, &mm->context.pgtable_list);
	}
	table = (unsigned long *) page_to_phys(page);
	while (page->flags & bits) {
		table += 256;
		bits <<= 1;
	}
	page->flags |= bits;
	if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
		list_move_tail(&page->lru, &mm->context.pgtable_list);
	spin_unlock_bh(&mm->context.list_lock);
	return table;
}

static void __page_table_free(struct mm_struct *mm, unsigned long *table)
{
	struct page *page;
	unsigned long bits;

	bits = ((unsigned long) table) & 15;
	table = (unsigned long *)(((unsigned long) table) ^ bits);
	page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
	page->flags ^= bits;
	if (!(page->flags & FRAG_MASK)) {
		pgtable_page_dtor(page);
		__free_page(page);
	}
}

void page_table_free(struct mm_struct *mm, unsigned long *table)
{
	struct page *page;
	unsigned long bits;

	bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
	bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
	page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
	spin_lock_bh(&mm->context.list_lock);
	page->flags ^= bits;
	if (page->flags & FRAG_MASK) {
		/* Page now has some free pgtable fragments. */
		if (!list_empty(&page->lru))
			list_move(&page->lru, &mm->context.pgtable_list);
		page = NULL;
	} else
		/* All fragments of the 4K page have been freed. */
		list_del(&page->lru);
	spin_unlock_bh(&mm->context.list_lock);
	if (page) {
		pgtable_page_dtor(page);
		__free_page(page);
	}
}

void page_table_free_rcu(struct mm_struct *mm, unsigned long *table)
{
	struct rcu_table_freelist *batch;
	struct page *page;
	unsigned long bits;

	if (atomic_read(&mm->mm_users) < 2 &&
	    cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
		page_table_free(mm, table);
		return;
	}
	batch = rcu_table_freelist_get(mm);
	if (!batch) {
		smp_call_function(smp_sync, NULL, 1);
		page_table_free(mm, table);
		return;
	}
	bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
	bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
	page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
	spin_lock_bh(&mm->context.list_lock);
	/* Delayed freeing with rcu prevents reuse of pgtable fragments */
	list_del_init(&page->lru);
	spin_unlock_bh(&mm->context.list_lock);
	table = (unsigned long *)(((unsigned long) table) | bits);
	batch->table[batch->pgt_index++] = table;
	if (batch->pgt_index >= batch->crst_index)
		rcu_table_freelist_finish();
}

void disable_noexec(struct mm_struct *mm, struct task_struct *tsk)
{
	struct page *page;

	spin_lock_bh(&mm->context.list_lock);
	/* Free shadow region and segment tables. */
	list_for_each_entry(page, &mm->context.crst_list, lru)
		if (page->index) {
			free_pages((unsigned long) page->index, ALLOC_ORDER);
			page->index = 0;
		}
	/* "Free" second halves of page tables. */
	list_for_each_entry(page, &mm->context.pgtable_list, lru)
		page->flags &= ~SECOND_HALVES;
	spin_unlock_bh(&mm->context.list_lock);
	mm->context.noexec = 0;
	update_mm(mm, tsk);
}

/*
 * switch on pgstes for its userspace process (for kvm)
 */
int s390_enable_sie(void)
{
	struct task_struct *tsk = current;
	struct mm_struct *mm, *old_mm;

	/* Do we have switched amode? If no, we cannot do sie */
	if (user_mode == HOME_SPACE_MODE)
		return -EINVAL;

	/* Do we have pgstes? if yes, we are done */
	if (tsk->mm->context.has_pgste)
		return 0;

	/* lets check if we are allowed to replace the mm */
	task_lock(tsk);
	if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
#ifdef CONFIG_AIO
	    !hlist_empty(&tsk->mm->ioctx_list) ||
#endif
	    tsk->mm != tsk->active_mm) {
		task_unlock(tsk);
		return -EINVAL;
	}
	task_unlock(tsk);

	/* we copy the mm and let dup_mm create the page tables with_pgstes */
	tsk->mm->context.alloc_pgste = 1;
	mm = dup_mm(tsk);
	tsk->mm->context.alloc_pgste = 0;
	if (!mm)
		return -ENOMEM;

	/* Now lets check again if something happened */
	task_lock(tsk);
	if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
#ifdef CONFIG_AIO
	    !hlist_empty(&tsk->mm->ioctx_list) ||
#endif
	    tsk->mm != tsk->active_mm) {
		mmput(mm);
		task_unlock(tsk);
		return -EINVAL;
	}

	/* ok, we are alone. No ptrace, no threads, etc. */
	old_mm = tsk->mm;
	tsk->mm = tsk->active_mm = mm;
	preempt_disable();
	update_mm(mm, tsk);
	atomic_inc(&mm->context.attach_count);
	atomic_dec(&old_mm->context.attach_count);
	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
	preempt_enable();
	task_unlock(tsk);
	mmput(old_mm);
	return 0;
}
EXPORT_SYMBOL_GPL(s390_enable_sie);

#if defined(CONFIG_DEBUG_PAGEALLOC) && defined(CONFIG_HIBERNATION)
bool kernel_page_present(struct page *page)
{
	unsigned long addr;
	int cc;

	addr = page_to_phys(page);
	asm volatile(
		"	lra	%1,0(%1)\n"
		"	ipm	%0\n"
		"	srl	%0,28"
		: "=d" (cc), "+a" (addr) : : "cc");
	return cc == 0;
}
#endif /* CONFIG_HIBERNATION && CONFIG_DEBUG_PAGEALLOC */