Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 714 insertions, 0 deletions

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
new file mode 100644
index 000000000..2de48b2c1
--- /dev/null
+++ b/arch/s390/mm/pgalloc.c
@@ -0,0 +1,714 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Page table allocation functions
+ *
+ *    Copyright IBM Corp. 2016
+ *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
+ */
+
+#include <linux/sysctl.h>
+#include <linux/slab.h>
+#include <linux/mm.h>
+#include <asm/mmu_context.h>
+#include <asm/pgalloc.h>
+#include <asm/gmap.h>
+#include <asm/tlb.h>
+#include <asm/tlbflush.h>
+
+#ifdef CONFIG_PGSTE
+
+int page_table_allocate_pgste = 0;
+EXPORT_SYMBOL(page_table_allocate_pgste);
+
+static struct ctl_table page_table_sysctl[] = {
+	{
+		.procname	= "allocate_pgste",
+		.data		= &page_table_allocate_pgste,
+		.maxlen		= sizeof(int),
+		.mode		= S_IRUGO | S_IWUSR,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+	{ }
+};
+
+static struct ctl_table page_table_sysctl_dir[] = {
+	{
+		.procname	= "vm",
+		.maxlen		= 0,
+		.mode		= 0555,
+		.child		= page_table_sysctl,
+	},
+	{ }
+};
+
+static int __init page_table_register_sysctl(void)
+{
+	return register_sysctl_table(page_table_sysctl_dir) ? 0 : -ENOMEM;
+}
+__initcall(page_table_register_sysctl);
+
+#endif /* CONFIG_PGSTE */
+
+unsigned long *crst_table_alloc(struct mm_struct *mm)
+{
+	struct page *page = alloc_pages(GFP_KERNEL, CRST_ALLOC_ORDER);
+
+	if (!page)
+		return NULL;
+	arch_set_page_dat(page, CRST_ALLOC_ORDER);
+	return (unsigned long *) page_to_virt(page);
+}
+
+void crst_table_free(struct mm_struct *mm, unsigned long *table)
+{
+	free_pages((unsigned long)table, CRST_ALLOC_ORDER);
+}
+
+static void __crst_table_upgrade(void *arg)
+{
+	struct mm_struct *mm = arg;
+
+	/* change all active ASCEs to avoid the creation of new TLBs */
+	if (current->active_mm == mm) {
+		S390_lowcore.user_asce = mm->context.asce;
+		__ctl_load(S390_lowcore.user_asce, 7, 7);
+	}
+	__tlb_flush_local();
+}
+
+int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
+{
+	unsigned long *pgd = NULL, *p4d = NULL, *__pgd;
+	unsigned long asce_limit = mm->context.asce_limit;
+
+	/* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */
+	VM_BUG_ON(asce_limit < _REGION2_SIZE);
+
+	if (end <= asce_limit)
+		return 0;
+
+	if (asce_limit == _REGION2_SIZE) {
+		p4d = crst_table_alloc(mm);
+		if (unlikely(!p4d))
+			goto err_p4d;
+		crst_table_init(p4d, _REGION2_ENTRY_EMPTY);
+	}
+	if (end > _REGION1_SIZE) {
+		pgd = crst_table_alloc(mm);
+		if (unlikely(!pgd))
+			goto err_pgd;
+		crst_table_init(pgd, _REGION1_ENTRY_EMPTY);
+	}
+
+	spin_lock_bh(&mm->page_table_lock);
+
+	/*
+	 * This routine gets called with mmap_lock lock held and there is
+	 * no reason to optimize for the case of otherwise. However, if
+	 * that would ever change, the below check will let us know.
+	 */
+	VM_BUG_ON(asce_limit != mm->context.asce_limit);
+
+	if (p4d) {
+		__pgd = (unsigned long *) mm->pgd;
+		p4d_populate(mm, (p4d_t *) p4d, (pud_t *) __pgd);
+		mm->pgd = (pgd_t *) p4d;
+		mm->context.asce_limit = _REGION1_SIZE;
+		mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
+			_ASCE_USER_BITS | _ASCE_TYPE_REGION2;
+		mm_inc_nr_puds(mm);
+	}
+	if (pgd) {
+		__pgd = (unsigned long *) mm->pgd;
+		pgd_populate(mm, (pgd_t *) pgd, (p4d_t *) __pgd);
+		mm->pgd = (pgd_t *) pgd;
+		mm->context.asce_limit = TASK_SIZE_MAX;
+		mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
+			_ASCE_USER_BITS | _ASCE_TYPE_REGION1;
+	}
+
+	spin_unlock_bh(&mm->page_table_lock);
+
+	on_each_cpu(__crst_table_upgrade, mm, 0);
+
+	return 0;
+
+err_pgd:
+	crst_table_free(mm, p4d);
+err_p4d:
+	return -ENOMEM;
+}
+
+static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
+{
+	unsigned int old, new;
+
+	do {
+		old = atomic_read(v);
+		new = old ^ bits;
+	} while (atomic_cmpxchg(v, old, new) != old);
+	return new;
+}
+
+#ifdef CONFIG_PGSTE
+
+struct page *page_table_alloc_pgste(struct mm_struct *mm)
+{
+	struct page *page;
+	u64 *table;
+
+	page = alloc_page(GFP_KERNEL);
+	if (page) {
+		table = (u64 *)page_to_virt(page);
+		memset64(table, _PAGE_INVALID, PTRS_PER_PTE);
+		memset64(table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
+	}
+	return page;
+}
+
+void page_table_free_pgste(struct page *page)
+{
+	__free_page(page);
+}
+
+#endif /* CONFIG_PGSTE */
+
+/*
+ * A 2KB-pgtable is either upper or lower half of a normal page.
+ * The second half of the page may be unused or used as another
+ * 2KB-pgtable.
+ *
+ * Whenever possible the parent page for a new 2KB-pgtable is picked
+ * from the list of partially allocated pages mm_context_t::pgtable_list.
+ * In case the list is empty a new parent page is allocated and added to
+ * the list.
+ *
+ * When a parent page gets fully allocated it contains 2KB-pgtables in both
+ * upper and lower halves and is removed from mm_context_t::pgtable_list.
+ *
+ * When 2KB-pgtable is freed from to fully allocated parent page that
+ * page turns partially allocated and added to mm_context_t::pgtable_list.
+ *
+ * If 2KB-pgtable is freed from the partially allocated parent page that
+ * page turns unused and gets removed from mm_context_t::pgtable_list.
+ * Furthermore, the unused parent page is released.
+ *
+ * As follows from the above, no unallocated or fully allocated parent
+ * pages are contained in mm_context_t::pgtable_list.
+ *
+ * The upper byte (bits 24-31) of the parent page _refcount is used
+ * for tracking contained 2KB-pgtables and has the following format:
+ *
+ *   PP  AA
+ * 01234567    upper byte (bits 24-31) of struct page::_refcount
+ *   ||  ||
+ *   ||  |+--- upper 2KB-pgtable is allocated
+ *   ||  +---- lower 2KB-pgtable is allocated
+ *   |+------- upper 2KB-pgtable is pending for removal
+ *   +-------- lower 2KB-pgtable is pending for removal
+ *
+ * (See commit 620b4e903179 ("s390: use _refcount for pgtables") on why
+ * using _refcount is possible).
+ *
+ * When 2KB-pgtable is allocated the corresponding AA bit is set to 1.
+ * The parent page is either:
+ *   - added to mm_context_t::pgtable_list in case the second half of the
+ *     parent page is still unallocated;
+ *   - removed from mm_context_t::pgtable_list in case both hales of the
+ *     parent page are allocated;
+ * These operations are protected with mm_context_t::lock.
+ *
+ * When 2KB-pgtable is deallocated the corresponding AA bit is set to 0
+ * and the corresponding PP bit is set to 1 in a single atomic operation.
+ * Thus, PP and AA bits corresponding to the same 2KB-pgtable are mutually
+ * exclusive and may never be both set to 1!
+ * The parent page is either:
+ *   - added to mm_context_t::pgtable_list in case the second half of the
+ *     parent page is still allocated;
+ *   - removed from mm_context_t::pgtable_list in case the second half of
+ *     the parent page is unallocated;
+ * These operations are protected with mm_context_t::lock.
+ *
+ * It is important to understand that mm_context_t::lock only protects
+ * mm_context_t::pgtable_list and AA bits, but not the parent page itself
+ * and PP bits.
+ *
+ * Releasing the parent page happens whenever the PP bit turns from 1 to 0,
+ * while both AA bits and the second PP bit are already unset. Then the
+ * parent page does not contain any 2KB-pgtable fragment anymore, and it has
+ * also been removed from mm_context_t::pgtable_list. It is safe to release
+ * the page therefore.
+ *
+ * PGSTE memory spaces use full 4KB-pgtables and do not need most of the
+ * logic described above. Both AA bits are set to 1 to denote a 4KB-pgtable
+ * while the PP bits are never used, nor such a page is added to or removed
+ * from mm_context_t::pgtable_list.
+ */
+unsigned long *page_table_alloc(struct mm_struct *mm)
+{
+	unsigned long *table;
+	struct page *page;
+	unsigned int mask, bit;
+
+	/* Try to get a fragment of a 4K page as a 2K page table */
+	if (!mm_alloc_pgste(mm)) {
+		table = NULL;
+		spin_lock_bh(&mm->context.lock);
+		if (!list_empty(&mm->context.pgtable_list)) {
+			page = list_first_entry(&mm->context.pgtable_list,
+						struct page, lru);
+			mask = atomic_read(&page->_refcount) >> 24;
+			/*
+			 * The pending removal bits must also be checked.
+			 * Failure to do so might lead to an impossible
+			 * value of (i.e 0x13 or 0x23) written to _refcount.
+			 * Such values violate the assumption that pending and
+			 * allocation bits are mutually exclusive, and the rest
+			 * of the code unrails as result. That could lead to
+			 * a whole bunch of races and corruptions.
+			 */
+			mask = (mask | (mask >> 4)) & 0x03U;
+			if (mask != 0x03U) {
+				table = (unsigned long *) page_to_virt(page);
+				bit = mask & 1;		/* =1 -> second 2K */
+				if (bit)
+					table += PTRS_PER_PTE;
+				atomic_xor_bits(&page->_refcount,
+							0x01U << (bit + 24));
+				list_del(&page->lru);
+			}
+		}
+		spin_unlock_bh(&mm->context.lock);
+		if (table)
+			return table;
+	}
+	/* Allocate a fresh page */
+	page = alloc_page(GFP_KERNEL);
+	if (!page)
+		return NULL;
+	if (!pgtable_pte_page_ctor(page)) {
+		__free_page(page);
+		return NULL;
+	}
+	arch_set_page_dat(page, 0);
+	/* Initialize page table */
+	table = (unsigned long *) page_to_virt(page);
+	if (mm_alloc_pgste(mm)) {
+		/* Return 4K page table with PGSTEs */
+		atomic_xor_bits(&page->_refcount, 0x03U << 24);
+		memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE);
+		memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
+	} else {
+		/* Return the first 2K fragment of the page */
+		atomic_xor_bits(&page->_refcount, 0x01U << 24);
+		memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE);
+		spin_lock_bh(&mm->context.lock);
+		list_add(&page->lru, &mm->context.pgtable_list);
+		spin_unlock_bh(&mm->context.lock);
+	}
+	return table;
+}
+
+static void page_table_release_check(struct page *page, void *table,
+				     unsigned int half, unsigned int mask)
+{
+	char msg[128];
+
+	if (!IS_ENABLED(CONFIG_DEBUG_VM) || !mask)
+		return;
+	snprintf(msg, sizeof(msg),
+		 "Invalid pgtable %p release half 0x%02x mask 0x%02x",
+		 table, half, mask);
+	dump_page(page, msg);
+}
+
+void page_table_free(struct mm_struct *mm, unsigned long *table)
+{
+	unsigned int mask, bit, half;
+	struct page *page;
+
+	page = virt_to_page(table);
+	if (!mm_alloc_pgste(mm)) {
+		/* Free 2K page table fragment of a 4K page */
+		bit = ((unsigned long) table & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t));
+		spin_lock_bh(&mm->context.lock);
+		/*
+		 * Mark the page for delayed release. The actual release
+		 * will happen outside of the critical section from this
+		 * function or from __tlb_remove_table()
+		 */
+		mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24));
+		mask >>= 24;
+		if (mask & 0x03U)
+			list_add(&page->lru, &mm->context.pgtable_list);
+		else
+			list_del(&page->lru);
+		spin_unlock_bh(&mm->context.lock);
+		mask = atomic_xor_bits(&page->_refcount, 0x10U << (bit + 24));
+		mask >>= 24;
+		if (mask != 0x00U)
+			return;
+		half = 0x01U << bit;
+	} else {
+		half = 0x03U;
+		mask = atomic_xor_bits(&page->_refcount, 0x03U << 24);
+		mask >>= 24;
+	}
+
+	page_table_release_check(page, table, half, mask);
+	pgtable_pte_page_dtor(page);
+	__free_page(page);
+}
+
+void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table,
+			 unsigned long vmaddr)
+{
+	struct mm_struct *mm;
+	struct page *page;
+	unsigned int bit, mask;
+
+	mm = tlb->mm;
+	page = virt_to_page(table);
+	if (mm_alloc_pgste(mm)) {
+		gmap_unlink(mm, table, vmaddr);
+		table = (unsigned long *) ((unsigned long)table | 0x03U);
+		tlb_remove_table(tlb, table);
+		return;
+	}
+	bit = ((unsigned long) table & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t));
+	spin_lock_bh(&mm->context.lock);
+	/*
+	 * Mark the page for delayed release. The actual release will happen
+	 * outside of the critical section from __tlb_remove_table() or from
+	 * page_table_free()
+	 */
+	mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24));
+	mask >>= 24;
+	if (mask & 0x03U)
+		list_add_tail(&page->lru, &mm->context.pgtable_list);
+	else
+		list_del(&page->lru);
+	spin_unlock_bh(&mm->context.lock);
+	table = (unsigned long *) ((unsigned long) table | (0x01U << bit));
+	tlb_remove_table(tlb, table);
+}
+
+void __tlb_remove_table(void *_table)
+{
+	unsigned int mask = (unsigned long) _table & 0x03U, half = mask;
+	void *table = (void *)((unsigned long) _table ^ mask);
+	struct page *page = virt_to_page(table);
+
+	switch (half) {
+	case 0x00U:	/* pmd, pud, or p4d */
+		free_pages((unsigned long)table, CRST_ALLOC_ORDER);
+		return;
+	case 0x01U:	/* lower 2K of a 4K page table */
+	case 0x02U:	/* higher 2K of a 4K page table */
+		mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24));
+		mask >>= 24;
+		if (mask != 0x00U)
+			return;
+		break;
+	case 0x03U:	/* 4K page table with pgstes */
+		mask = atomic_xor_bits(&page->_refcount, 0x03U << 24);
+		mask >>= 24;
+		break;
+	}
+
+	page_table_release_check(page, table, half, mask);
+	pgtable_pte_page_dtor(page);
+	__free_page(page);
+}
+
+/*
+ * Base infrastructure required to generate basic asces, region, segment,
+ * and page tables that do not make use of enhanced features like EDAT1.
+ */
+
+static struct kmem_cache *base_pgt_cache;
+
+static unsigned long *base_pgt_alloc(void)
+{
+	unsigned long *table;
+
+	table = kmem_cache_alloc(base_pgt_cache, GFP_KERNEL);
+	if (table)
+		memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE);
+	return table;
+}
+
+static void base_pgt_free(unsigned long *table)
+{
+	kmem_cache_free(base_pgt_cache, table);
+}
+
+static unsigned long *base_crst_alloc(unsigned long val)
+{
+	unsigned long *table;
+
+	table =	(unsigned long *)__get_free_pages(GFP_KERNEL, CRST_ALLOC_ORDER);
+	if (table)
+		crst_table_init(table, val);
+	return table;
+}
+
+static void base_crst_free(unsigned long *table)
+{
+	free_pages((unsigned long)table, CRST_ALLOC_ORDER);
+}
+
+#define BASE_ADDR_END_FUNC(NAME, SIZE)					\
+static inline unsigned long base_##NAME##_addr_end(unsigned long addr,	\
+						   unsigned long end)	\
+{									\
+	unsigned long next = (addr + (SIZE)) & ~((SIZE) - 1);		\
+									\
+	return (next - 1) < (end - 1) ? next : end;			\
+}
+
+BASE_ADDR_END_FUNC(page,    _PAGE_SIZE)
+BASE_ADDR_END_FUNC(segment, _SEGMENT_SIZE)
+BASE_ADDR_END_FUNC(region3, _REGION3_SIZE)
+BASE_ADDR_END_FUNC(region2, _REGION2_SIZE)
+BASE_ADDR_END_FUNC(region1, _REGION1_SIZE)
+
+static inline unsigned long base_lra(unsigned long address)
+{
+	unsigned long real;
+
+	asm volatile(
+		"	lra	%0,0(%1)\n"
+		: "=d" (real) : "a" (address) : "cc");
+	return real;
+}
+
+static int base_page_walk(unsigned long *origin, unsigned long addr,
+			  unsigned long end, int alloc)
+{
+	unsigned long *pte, next;
+
+	if (!alloc)
+		return 0;
+	pte = origin;
+	pte += (addr & _PAGE_INDEX) >> _PAGE_SHIFT;
+	do {
+		next = base_page_addr_end(addr, end);
+		*pte = base_lra(addr);
+	} while (pte++, addr = next, addr < end);
+	return 0;
+}
+
+static int base_segment_walk(unsigned long *origin, unsigned long addr,
+			     unsigned long end, int alloc)
+{
+	unsigned long *ste, next, *table;
+	int rc;
+
+	ste = origin;
+	ste += (addr & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
+	do {
+		next = base_segment_addr_end(addr, end);
+		if (*ste & _SEGMENT_ENTRY_INVALID) {
+			if (!alloc)
+				continue;
+			table = base_pgt_alloc();
+			if (!table)
+				return -ENOMEM;
+			*ste = __pa(table) | _SEGMENT_ENTRY;
+		}
+		table = __va(*ste & _SEGMENT_ENTRY_ORIGIN);
+		rc = base_page_walk(table, addr, next, alloc);
+		if (rc)
+			return rc;
+		if (!alloc)
+			base_pgt_free(table);
+		cond_resched();
+	} while (ste++, addr = next, addr < end);
+	return 0;
+}
+
+static int base_region3_walk(unsigned long *origin, unsigned long addr,
+			     unsigned long end, int alloc)
+{
+	unsigned long *rtte, next, *table;
+	int rc;
+
+	rtte = origin;
+	rtte += (addr & _REGION3_INDEX) >> _REGION3_SHIFT;
+	do {
+		next = base_region3_addr_end(addr, end);
+		if (*rtte & _REGION_ENTRY_INVALID) {
+			if (!alloc)
+				continue;
+			table = base_crst_alloc(_SEGMENT_ENTRY_EMPTY);
+			if (!table)
+				return -ENOMEM;
+			*rtte = __pa(table) | _REGION3_ENTRY;
+		}
+		table = __va(*rtte & _REGION_ENTRY_ORIGIN);
+		rc = base_segment_walk(table, addr, next, alloc);
+		if (rc)
+			return rc;
+		if (!alloc)
+			base_crst_free(table);
+	} while (rtte++, addr = next, addr < end);
+	return 0;
+}
+
+static int base_region2_walk(unsigned long *origin, unsigned long addr,
+			     unsigned long end, int alloc)
+{
+	unsigned long *rste, next, *table;
+	int rc;
+
+	rste = origin;
+	rste += (addr & _REGION2_INDEX) >> _REGION2_SHIFT;
+	do {
+		next = base_region2_addr_end(addr, end);
+		if (*rste & _REGION_ENTRY_INVALID) {
+			if (!alloc)
+				continue;
+			table = base_crst_alloc(_REGION3_ENTRY_EMPTY);
+			if (!table)
+				return -ENOMEM;
+			*rste = __pa(table) | _REGION2_ENTRY;
+		}
+		table = __va(*rste & _REGION_ENTRY_ORIGIN);
+		rc = base_region3_walk(table, addr, next, alloc);
+		if (rc)
+			return rc;
+		if (!alloc)
+			base_crst_free(table);
+	} while (rste++, addr = next, addr < end);
+	return 0;
+}
+
+static int base_region1_walk(unsigned long *origin, unsigned long addr,
+			     unsigned long end, int alloc)
+{
+	unsigned long *rfte, next, *table;
+	int rc;
+
+	rfte = origin;
+	rfte += (addr & _REGION1_INDEX) >> _REGION1_SHIFT;
+	do {
+		next = base_region1_addr_end(addr, end);
+		if (*rfte & _REGION_ENTRY_INVALID) {
+			if (!alloc)
+				continue;
+			table = base_crst_alloc(_REGION2_ENTRY_EMPTY);
+			if (!table)
+				return -ENOMEM;
+			*rfte = __pa(table) | _REGION1_ENTRY;
+		}
+		table = __va(*rfte & _REGION_ENTRY_ORIGIN);
+		rc = base_region2_walk(table, addr, next, alloc);
+		if (rc)
+			return rc;
+		if (!alloc)
+			base_crst_free(table);
+	} while (rfte++, addr = next, addr < end);
+	return 0;
+}
+
+/**
+ * base_asce_free - free asce and tables returned from base_asce_alloc()
+ * @asce: asce to be freed
+ *
+ * Frees all region, segment, and page tables that were allocated with a
+ * corresponding base_asce_alloc() call.
+ */
+void base_asce_free(unsigned long asce)
+{
+	unsigned long *table = __va(asce & _ASCE_ORIGIN);
+
+	if (!asce)
+		return;
+	switch (asce & _ASCE_TYPE_MASK) {
+	case _ASCE_TYPE_SEGMENT:
+		base_segment_walk(table, 0, _REGION3_SIZE, 0);
+		break;
+	case _ASCE_TYPE_REGION3:
+		base_region3_walk(table, 0, _REGION2_SIZE, 0);
+		break;
+	case _ASCE_TYPE_REGION2:
+		base_region2_walk(table, 0, _REGION1_SIZE, 0);
+		break;
+	case _ASCE_TYPE_REGION1:
+		base_region1_walk(table, 0, TASK_SIZE_MAX, 0);
+		break;
+	}
+	base_crst_free(table);
+}
+
+static int base_pgt_cache_init(void)
+{
+	static DEFINE_MUTEX(base_pgt_cache_mutex);
+	unsigned long sz = _PAGE_TABLE_SIZE;
+
+	if (base_pgt_cache)
+		return 0;
+	mutex_lock(&base_pgt_cache_mutex);
+	if (!base_pgt_cache)
+		base_pgt_cache = kmem_cache_create("base_pgt", sz, sz, 0, NULL);
+	mutex_unlock(&base_pgt_cache_mutex);
+	return base_pgt_cache ? 0 : -ENOMEM;
+}
+
+/**
+ * base_asce_alloc - create kernel mapping without enhanced DAT features
+ * @addr: virtual start address of kernel mapping
+ * @num_pages: number of consecutive pages
+ *
+ * Generate an asce, including all required region, segment and page tables,
+ * that can be used to access the virtual kernel mapping. The difference is
+ * that the returned asce does not make use of any enhanced DAT features like
+ * e.g. large pages. This is required for some I/O functions that pass an
+ * asce, like e.g. some service call requests.
+ *
+ * Note: the returned asce may NEVER be attached to any cpu. It may only be
+ *	 used for I/O requests. tlb entries that might result because the
+ *	 asce was attached to a cpu won't be cleared.
+ */
+unsigned long base_asce_alloc(unsigned long addr, unsigned long num_pages)
+{
+	unsigned long asce, *table, end;
+	int rc;
+
+	if (base_pgt_cache_init())
+		return 0;
+	end = addr + num_pages * PAGE_SIZE;
+	if (end <= _REGION3_SIZE) {
+		table = base_crst_alloc(_SEGMENT_ENTRY_EMPTY);
+		if (!table)
+			return 0;
+		rc = base_segment_walk(table, addr, end, 1);
+		asce = __pa(table) | _ASCE_TYPE_SEGMENT | _ASCE_TABLE_LENGTH;
+	} else if (end <= _REGION2_SIZE) {
+		table = base_crst_alloc(_REGION3_ENTRY_EMPTY);
+		if (!table)
+			return 0;
+		rc = base_region3_walk(table, addr, end, 1);
+		asce = __pa(table) | _ASCE_TYPE_REGION3 | _ASCE_TABLE_LENGTH;
+	} else if (end <= _REGION1_SIZE) {
+		table = base_crst_alloc(_REGION2_ENTRY_EMPTY);
+		if (!table)
+			return 0;
+		rc = base_region2_walk(table, addr, end, 1);
+		asce = __pa(table) | _ASCE_TYPE_REGION2 | _ASCE_TABLE_LENGTH;
+	} else {
+		table = base_crst_alloc(_REGION1_ENTRY_EMPTY);
+		if (!table)
+			return 0;
+		rc = base_region1_walk(table, addr, end, 1);
+		asce = __pa(table) | _ASCE_TYPE_REGION1 | _ASCE_TABLE_LENGTH;
+	}
+	if (rc) {
+		base_asce_free(asce);
+		asce = 0;
+	}
+	return asce;
+}