arch/sparc64/mm/tsb.c - arm/linux-arm64-legacy - Git at Google

 /* arch/sparc64/mm/tsb.c
  *
  * Copyright (C) 2006 David S. Miller <davem@davemloft.net>
  */

 #include <linux/kernel.h>
 #include <asm/system.h>
 #include <asm/page.h>
 #include <asm/tlbflush.h>
 #include <asm/tlb.h>
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 #include <asm/tsb.h>
 #include <asm/oplib.h>

 extern struct tsb swapper_tsb[KERNEL_TSB_NENTRIES];

 static inline unsigned long tsb_hash(unsigned long vaddr, unsigned long nentries)
 {
 	vaddr >>= PAGE_SHIFT;
 	return vaddr & (nentries - 1);
 }

 static inline int tag_compare(unsigned long tag, unsigned long vaddr)
 {
 	return (tag == (vaddr >> 22));
 }

 /* TSB flushes need only occur on the processor initiating the address
  * space modification, not on each cpu the address space has run on.
  * Only the TLB flush needs that treatment.
  */

 void flush_tsb_kernel_range(unsigned long start, unsigned long end)
 {
 	unsigned long v;

 	for (v = start; v < end; v += PAGE_SIZE) {
 		unsigned long hash = tsb_hash(v, KERNEL_TSB_NENTRIES);
 		struct tsb *ent = &swapper_tsb[hash];

 		if (tag_compare(ent->tag, v)) {
 			ent->tag = (1UL << TSB_TAG_INVALID_BIT);
 			membar_storeload_storestore();
 		}
 	}
 }

 void flush_tsb_user(struct mmu_gather *mp)
 {
 	struct mm_struct *mm = mp->mm;
 	unsigned long nentries, base, flags;
 	struct tsb *tsb;
 	int i;

 	spin_lock_irqsave(&mm->context.lock, flags);

 	tsb = mm->context.tsb;
 	nentries = mm->context.tsb_nentries;

 	if (tlb_type == cheetah_plus || tlb_type == hypervisor)
 		base = __pa(tsb);
 	else
 		base = (unsigned long) tsb;

 	for (i = 0; i < mp->tlb_nr; i++) {
 		unsigned long v = mp->vaddrs[i];
 		unsigned long tag, ent, hash;

 		v &= ~0x1UL;

 		hash = tsb_hash(v, nentries);
 		ent = base + (hash * sizeof(struct tsb));
 		tag = (v >> 22UL);

 		tsb_flush(ent, tag);
 	}

 	spin_unlock_irqrestore(&mm->context.lock, flags);
 }

 static void setup_tsb_params(struct mm_struct *mm, unsigned long tsb_bytes)
 {
 	unsigned long tsb_reg, base, tsb_paddr;
 	unsigned long page_sz, tte;

 	mm->context.tsb_nentries = tsb_bytes / sizeof(struct tsb);

 	base = TSBMAP_BASE;
 	tte = pgprot_val(PAGE_KERNEL_LOCKED);
 	tsb_paddr = __pa(mm->context.tsb);
 	BUG_ON(tsb_paddr & (tsb_bytes - 1UL));

 	/* Use the smallest page size that can map the whole TSB
 	 * in one TLB entry.
 	 */
 	switch (tsb_bytes) {
 	case 8192 << 0:
 		tsb_reg = 0x0UL;
 #ifdef DCACHE_ALIASING_POSSIBLE
 		base += (tsb_paddr & 8192);
 #endif
 		page_sz = 8192;
 		break;

 	case 8192 << 1:
 		tsb_reg = 0x1UL;
 		page_sz = 64 * 1024;
 		break;

 	case 8192 << 2:
 		tsb_reg = 0x2UL;
 		page_sz = 64 * 1024;
 		break;

 	case 8192 << 3:
 		tsb_reg = 0x3UL;
 		page_sz = 64 * 1024;
 		break;

 	case 8192 << 4:
 		tsb_reg = 0x4UL;
 		page_sz = 512 * 1024;
 		break;

 	case 8192 << 5:
 		tsb_reg = 0x5UL;
 		page_sz = 512 * 1024;
 		break;

 	case 8192 << 6:
 		tsb_reg = 0x6UL;
 		page_sz = 512 * 1024;
 		break;

 	case 8192 << 7:
 		tsb_reg = 0x7UL;
 		page_sz = 4 * 1024 * 1024;
 		break;

 	default:
 		BUG();
 	};
 	tte |= pte_sz_bits(page_sz);

 	if (tlb_type == cheetah_plus || tlb_type == hypervisor) {
 		/* Physical mapping, no locked TLB entry for TSB.  */
 		tsb_reg |= tsb_paddr;

 		mm->context.tsb_reg_val = tsb_reg;
 		mm->context.tsb_map_vaddr = 0;
 		mm->context.tsb_map_pte = 0;
 	} else {
 		tsb_reg |= base;
 		tsb_reg |= (tsb_paddr & (page_sz - 1UL));
 		tte |= (tsb_paddr & ~(page_sz - 1UL));

 		mm->context.tsb_reg_val = tsb_reg;
 		mm->context.tsb_map_vaddr = base;
 		mm->context.tsb_map_pte = tte;
 	}

 	/* Setup the Hypervisor TSB descriptor.  */
 	if (tlb_type == hypervisor) {
 		struct hv_tsb_descr *hp = &mm->context.tsb_descr;

 		switch (PAGE_SIZE) {
 		case 8192:
 		default:
 			hp->pgsz_idx = HV_PGSZ_IDX_8K;
 			break;

 		case 64 * 1024:
 			hp->pgsz_idx = HV_PGSZ_IDX_64K;
 			break;

 		case 512 * 1024:
 			hp->pgsz_idx = HV_PGSZ_IDX_512K;
 			break;

 		case 4 * 1024 * 1024:
 			hp->pgsz_idx = HV_PGSZ_IDX_4MB;
 			break;
 		};
 		hp->assoc = 1;
 		hp->num_ttes = tsb_bytes / 16;
 		hp->ctx_idx = 0;
 		switch (PAGE_SIZE) {
 		case 8192:
 		default:
 			hp->pgsz_mask = HV_PGSZ_MASK_8K;
 			break;

 		case 64 * 1024:
 			hp->pgsz_mask = HV_PGSZ_MASK_64K;
 			break;

 		case 512 * 1024:
 			hp->pgsz_mask = HV_PGSZ_MASK_512K;
 			break;

 		case 4 * 1024 * 1024:
 			hp->pgsz_mask = HV_PGSZ_MASK_4MB;
 			break;
 		};
 		hp->tsb_base = tsb_paddr;
 		hp->resv = 0;
 	}
 }

 static kmem_cache_t *tsb_caches[8] __read_mostly;

 static const char *tsb_cache_names[8] = {
 	"tsb_8KB",
 	"tsb_16KB",
 	"tsb_32KB",
 	"tsb_64KB",
 	"tsb_128KB",
 	"tsb_256KB",
 	"tsb_512KB",
 	"tsb_1MB",
 };

 void __init tsb_cache_init(void)
 {
 	unsigned long i;

 	for (i = 0; i < 8; i++) {
 		unsigned long size = 8192 << i;
 		const char *name = tsb_cache_names[i];

 		tsb_caches[i] = kmem_cache_create(name,
 						  size, size,
 						  SLAB_HWCACHE_ALIGN |
 						  SLAB_MUST_HWCACHE_ALIGN,
 						  NULL, NULL);
 		if (!tsb_caches[i]) {
 			prom_printf("Could not create %s cache\n", name);
 			prom_halt();
 		}
 	}
 }

 /* When the RSS of an address space exceeds mm->context.tsb_rss_limit,
  * do_sparc64_fault() invokes this routine to try and grow the TSB.
  *
  * When we reach the maximum TSB size supported, we stick ~0UL into
  * mm->context.tsb_rss_limit so the grow checks in update_mmu_cache()
  * will not trigger any longer.
  *
  * The TSB can be anywhere from 8K to 1MB in size, in increasing powers
  * of two.  The TSB must be aligned to it's size, so f.e. a 512K TSB
  * must be 512K aligned.  It also must be physically contiguous, so we
  * cannot use vmalloc().
  *
  * The idea here is to grow the TSB when the RSS of the process approaches
  * the number of entries that the current TSB can hold at once.  Currently,
  * we trigger when the RSS hits 3/4 of the TSB capacity.
  */
 void tsb_grow(struct mm_struct *mm, unsigned long rss)
 {
 	unsigned long max_tsb_size = 1 * 1024 * 1024;
 	unsigned long new_size, old_size, flags;
 	struct tsb *old_tsb, *new_tsb;
 	unsigned long new_cache_index, old_cache_index;
 	unsigned long new_rss_limit;
 	gfp_t gfp_flags;

 	if (max_tsb_size > (PAGE_SIZE << MAX_ORDER))
 		max_tsb_size = (PAGE_SIZE << MAX_ORDER);

 	new_cache_index = 0;
 	for (new_size = 8192; new_size < max_tsb_size; new_size <<= 1UL) {
 		unsigned long n_entries = new_size / sizeof(struct tsb);

 		n_entries = (n_entries * 3) / 4;
 		if (n_entries > rss)
 			break;

 		new_cache_index++;
 	}

 	if (new_size == max_tsb_size)
 		new_rss_limit = ~0UL;
 	else
 		new_rss_limit = ((new_size / sizeof(struct tsb)) * 3) / 4;

 retry_tsb_alloc:
 	gfp_flags = GFP_KERNEL;
 	if (new_size > (PAGE_SIZE * 2))
 		gfp_flags = __GFP_NOWARN | __GFP_NORETRY;

 	new_tsb = kmem_cache_alloc(tsb_caches[new_cache_index], gfp_flags);
 	if (unlikely(!new_tsb)) {
 		/* Not being able to fork due to a high-order TSB
 		 * allocation failure is very bad behavior.  Just back
 		 * down to a 0-order allocation and force no TSB
 		 * growing for this address space.
 		 */
 		if (mm->context.tsb == NULL && new_cache_index > 0) {
 			new_cache_index = 0;
 			new_size = 8192;
 			new_rss_limit = ~0UL;
 			goto retry_tsb_alloc;
 		}

 		/* If we failed on a TSB grow, we are under serious
 		 * memory pressure so don't try to grow any more.
 		 */
 		if (mm->context.tsb != NULL)
 			mm->context.tsb_rss_limit = ~0UL;
 		return;
 	}

 	/* Mark all tags as invalid.  */
 	tsb_init(new_tsb, new_size);

 	/* Ok, we are about to commit the changes.  If we are
 	 * growing an existing TSB the locking is very tricky,
 	 * so WATCH OUT!
 	 *
 	 * We have to hold mm->context.lock while committing to the
 	 * new TSB, this synchronizes us with processors in
 	 * flush_tsb_user() and switch_mm() for this address space.
 	 *
 	 * But even with that lock held, processors run asynchronously
 	 * accessing the old TSB via TLB miss handling.  This is OK
 	 * because those actions are just propagating state from the
 	 * Linux page tables into the TSB, page table mappings are not
 	 * being changed.  If a real fault occurs, the processor will
 	 * synchronize with us when it hits flush_tsb_user(), this is
 	 * also true for the case where vmscan is modifying the page
 	 * tables.  The only thing we need to be careful with is to
 	 * skip any locked TSB entries during copy_tsb().
 	 *
 	 * When we finish committing to the new TSB, we have to drop
 	 * the lock and ask all other cpus running this address space
 	 * to run tsb_context_switch() to see the new TSB table.
 	 */
 	spin_lock_irqsave(&mm->context.lock, flags);

 	old_tsb = mm->context.tsb;
 	old_cache_index = (mm->context.tsb_reg_val & 0x7UL);
 	old_size = mm->context.tsb_nentries * sizeof(struct tsb);


 	/* Handle multiple threads trying to grow the TSB at the same time.
 	 * One will get in here first, and bump the size and the RSS limit.
 	 * The others will get in here next and hit this check.
 	 */
 	if (unlikely(old_tsb && (rss < mm->context.tsb_rss_limit))) {
 		spin_unlock_irqrestore(&mm->context.lock, flags);

 		kmem_cache_free(tsb_caches[new_cache_index], new_tsb);
 		return;
 	}

 	mm->context.tsb_rss_limit = new_rss_limit;

 	if (old_tsb) {
 		extern void copy_tsb(unsigned long old_tsb_base,
 				     unsigned long old_tsb_size,
 				     unsigned long new_tsb_base,
 				     unsigned long new_tsb_size);
 		unsigned long old_tsb_base = (unsigned long) old_tsb;
 		unsigned long new_tsb_base = (unsigned long) new_tsb;

 		if (tlb_type == cheetah_plus || tlb_type == hypervisor) {
 			old_tsb_base = __pa(old_tsb_base);
 			new_tsb_base = __pa(new_tsb_base);
 		}
 		copy_tsb(old_tsb_base, old_size, new_tsb_base, new_size);
 	}

 	mm->context.tsb = new_tsb;
 	setup_tsb_params(mm, new_size);

 	spin_unlock_irqrestore(&mm->context.lock, flags);

 	/* If old_tsb is NULL, we're being invoked for the first time
 	 * from init_new_context().
 	 */
 	if (old_tsb) {
 		/* Reload it on the local cpu.  */
 		tsb_context_switch(mm);

 		/* Now force other processors to do the same.  */
 		smp_tsb_sync(mm);

 		/* Now it is safe to free the old tsb.  */
 		kmem_cache_free(tsb_caches[old_cache_index], old_tsb);
 	}
 }

 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 {
 	spin_lock_init(&mm->context.lock);

 	mm->context.sparc64_ctx_val = 0UL;

 	/* copy_mm() copies over the parent's mm_struct before calling
 	 * us, so we need to zero out the TSB pointer or else tsb_grow()
 	 * will be confused and think there is an older TSB to free up.
 	 */
 	mm->context.tsb = NULL;

 	/* If this is fork, inherit the parent's TSB size.  We would
 	 * grow it to that size on the first page fault anyways.
 	 */
 	tsb_grow(mm, get_mm_rss(mm));

 	if (unlikely(!mm->context.tsb))
 		return -ENOMEM;

 	return 0;
 }

 void destroy_context(struct mm_struct *mm)
 {
 	unsigned long flags, cache_index;

 	cache_index = (mm->context.tsb_reg_val & 0x7UL);
 	kmem_cache_free(tsb_caches[cache_index], mm->context.tsb);

 	/* We can remove these later, but for now it's useful
 	 * to catch any bogus post-destroy_context() references
 	 * to the TSB.
 	 */
 	mm->context.tsb = NULL;
 	mm->context.tsb_reg_val = 0UL;

 	spin_lock_irqsave(&ctx_alloc_lock, flags);

 	if (CTX_VALID(mm->context)) {
 		unsigned long nr = CTX_NRBITS(mm->context);
 		mmu_context_bmap[nr>>6] &= ~(1UL << (nr & 63));
 	}

 	spin_unlock_irqrestore(&ctx_alloc_lock, flags);
 }
	/* arch/sparc64/mm/tsb.c
	*
	* Copyright (C) 2006 David S. Miller <davem@davemloft.net>
	*/

	#include <linux/kernel.h>
	#include <asm/system.h>
	#include <asm/page.h>
	#include <asm/tlbflush.h>
	#include <asm/tlb.h>
	#include <asm/mmu_context.h>
	#include <asm/pgtable.h>
	#include <asm/tsb.h>
	#include <asm/oplib.h>

	extern struct tsb swapper_tsb[KERNEL_TSB_NENTRIES];

	static inline unsigned long tsb_hash(unsigned long vaddr, unsigned long nentries)
	{
	vaddr >>= PAGE_SHIFT;
	return vaddr & (nentries - 1);
	}

	static inline int tag_compare(unsigned long tag, unsigned long vaddr)
	{
	return (tag == (vaddr >> 22));
	}

	/* TSB flushes need only occur on the processor initiating the address
	* space modification, not on each cpu the address space has run on.
	* Only the TLB flush needs that treatment.
	*/

	void flush_tsb_kernel_range(unsigned long start, unsigned long end)
	{
	unsigned long v;

	for (v = start; v < end; v += PAGE_SIZE) {
	unsigned long hash = tsb_hash(v, KERNEL_TSB_NENTRIES);
	struct tsb *ent = &swapper_tsb[hash];

	if (tag_compare(ent->tag, v)) {
	ent->tag = (1UL << TSB_TAG_INVALID_BIT);
	membar_storeload_storestore();
	}
	}
	}

	void flush_tsb_user(struct mmu_gather *mp)
	{
	struct mm_struct *mm = mp->mm;
	unsigned long nentries, base, flags;
	struct tsb *tsb;
	int i;

	spin_lock_irqsave(&mm->context.lock, flags);

	tsb = mm->context.tsb;
	nentries = mm->context.tsb_nentries;

	if (tlb_type == cheetah_plus \|\| tlb_type == hypervisor)
	base = __pa(tsb);
	else
	base = (unsigned long) tsb;

	for (i = 0; i < mp->tlb_nr; i++) {
	unsigned long v = mp->vaddrs[i];
	unsigned long tag, ent, hash;

	v &= ~0x1UL;

	hash = tsb_hash(v, nentries);
	ent = base + (hash * sizeof(struct tsb));
	tag = (v >> 22UL);

	tsb_flush(ent, tag);
	}

	spin_unlock_irqrestore(&mm->context.lock, flags);
	}

	static void setup_tsb_params(struct mm_struct *mm, unsigned long tsb_bytes)
	{
	unsigned long tsb_reg, base, tsb_paddr;
	unsigned long page_sz, tte;

	mm->context.tsb_nentries = tsb_bytes / sizeof(struct tsb);

	base = TSBMAP_BASE;
	tte = pgprot_val(PAGE_KERNEL_LOCKED);
	tsb_paddr = __pa(mm->context.tsb);
	BUG_ON(tsb_paddr & (tsb_bytes - 1UL));

	/* Use the smallest page size that can map the whole TSB
	* in one TLB entry.
	*/
	switch (tsb_bytes) {
	case 8192 << 0:
	tsb_reg = 0x0UL;
	#ifdef DCACHE_ALIASING_POSSIBLE
	base += (tsb_paddr & 8192);
	#endif
	page_sz = 8192;
	break;

	case 8192 << 1:
	tsb_reg = 0x1UL;
	page_sz = 64 * 1024;
	break;

	case 8192 << 2:
	tsb_reg = 0x2UL;
	page_sz = 64 * 1024;
	break;

	case 8192 << 3:
	tsb_reg = 0x3UL;
	page_sz = 64 * 1024;
	break;

	case 8192 << 4:
	tsb_reg = 0x4UL;
	page_sz = 512 * 1024;
	break;

	case 8192 << 5:
	tsb_reg = 0x5UL;
	page_sz = 512 * 1024;
	break;

	case 8192 << 6:
	tsb_reg = 0x6UL;
	page_sz = 512 * 1024;
	break;

	case 8192 << 7:
	tsb_reg = 0x7UL;
	page_sz = 4 * 1024 * 1024;
	break;

	default:
	BUG();
	};
	tte \|= pte_sz_bits(page_sz);

	if (tlb_type == cheetah_plus \|\| tlb_type == hypervisor) {
	/* Physical mapping, no locked TLB entry for TSB. */
	tsb_reg \|= tsb_paddr;

	mm->context.tsb_reg_val = tsb_reg;
	mm->context.tsb_map_vaddr = 0;
	mm->context.tsb_map_pte = 0;
	} else {
	tsb_reg \|= base;
	tsb_reg \|= (tsb_paddr & (page_sz - 1UL));
	tte \|= (tsb_paddr & ~(page_sz - 1UL));

	mm->context.tsb_reg_val = tsb_reg;
	mm->context.tsb_map_vaddr = base;
	mm->context.tsb_map_pte = tte;
	}

	/* Setup the Hypervisor TSB descriptor. */
	if (tlb_type == hypervisor) {
	struct hv_tsb_descr *hp = &mm->context.tsb_descr;

	switch (PAGE_SIZE) {
	case 8192:
	default:
	hp->pgsz_idx = HV_PGSZ_IDX_8K;
	break;

	case 64 * 1024:
	hp->pgsz_idx = HV_PGSZ_IDX_64K;
	break;

	case 512 * 1024:
	hp->pgsz_idx = HV_PGSZ_IDX_512K;
	break;

	case 4 * 1024 * 1024:
	hp->pgsz_idx = HV_PGSZ_IDX_4MB;
	break;
	};
	hp->assoc = 1;
	hp->num_ttes = tsb_bytes / 16;
	hp->ctx_idx = 0;
	switch (PAGE_SIZE) {
	case 8192:
	default:
	hp->pgsz_mask = HV_PGSZ_MASK_8K;
	break;

	case 64 * 1024:
	hp->pgsz_mask = HV_PGSZ_MASK_64K;
	break;

	case 512 * 1024:
	hp->pgsz_mask = HV_PGSZ_MASK_512K;
	break;

	case 4 * 1024 * 1024:
	hp->pgsz_mask = HV_PGSZ_MASK_4MB;
	break;
	};
	hp->tsb_base = tsb_paddr;
	hp->resv = 0;
	}
	}

	static kmem_cache_t *tsb_caches[8] __read_mostly;

	static const char *tsb_cache_names[8] = {
	"tsb_8KB",
	"tsb_16KB",
	"tsb_32KB",
	"tsb_64KB",
	"tsb_128KB",
	"tsb_256KB",
	"tsb_512KB",
	"tsb_1MB",
	};

	void __init tsb_cache_init(void)
	{
	unsigned long i;

	for (i = 0; i < 8; i++) {
	unsigned long size = 8192 << i;
	const char *name = tsb_cache_names[i];

	tsb_caches[i] = kmem_cache_create(name,
	size, size,
	SLAB_HWCACHE_ALIGN \|
	SLAB_MUST_HWCACHE_ALIGN,
	NULL, NULL);
	if (!tsb_caches[i]) {
	prom_printf("Could not create %s cache\n", name);
	prom_halt();
	}
	}
	}

	/* When the RSS of an address space exceeds mm->context.tsb_rss_limit,
	* do_sparc64_fault() invokes this routine to try and grow the TSB.
	*
	* When we reach the maximum TSB size supported, we stick ~0UL into
	* mm->context.tsb_rss_limit so the grow checks in update_mmu_cache()
	* will not trigger any longer.
	*
	* The TSB can be anywhere from 8K to 1MB in size, in increasing powers
	* of two. The TSB must be aligned to it's size, so f.e. a 512K TSB
	* must be 512K aligned. It also must be physically contiguous, so we
	* cannot use vmalloc().
	*
	* The idea here is to grow the TSB when the RSS of the process approaches
	* the number of entries that the current TSB can hold at once. Currently,
	* we trigger when the RSS hits 3/4 of the TSB capacity.
	*/
	void tsb_grow(struct mm_struct *mm, unsigned long rss)
	{
	unsigned long max_tsb_size = 1 * 1024 * 1024;
	unsigned long new_size, old_size, flags;
	struct tsb old_tsb, new_tsb;
	unsigned long new_cache_index, old_cache_index;
	unsigned long new_rss_limit;
	gfp_t gfp_flags;

	if (max_tsb_size > (PAGE_SIZE << MAX_ORDER))
	max_tsb_size = (PAGE_SIZE << MAX_ORDER);

	new_cache_index = 0;
	for (new_size = 8192; new_size < max_tsb_size; new_size <<= 1UL) {
	unsigned long n_entries = new_size / sizeof(struct tsb);

	n_entries = (n_entries * 3) / 4;
	if (n_entries > rss)
	break;

	new_cache_index++;
	}

	if (new_size == max_tsb_size)
	new_rss_limit = ~0UL;
	else
	new_rss_limit = ((new_size / sizeof(struct tsb)) * 3) / 4;

	retry_tsb_alloc:
	gfp_flags = GFP_KERNEL;
	if (new_size > (PAGE_SIZE * 2))
	gfp_flags = __GFP_NOWARN \| __GFP_NORETRY;

	new_tsb = kmem_cache_alloc(tsb_caches[new_cache_index], gfp_flags);
	if (unlikely(!new_tsb)) {
	/* Not being able to fork due to a high-order TSB
	* allocation failure is very bad behavior. Just back
	* down to a 0-order allocation and force no TSB
	* growing for this address space.
	*/
	if (mm->context.tsb == NULL && new_cache_index > 0) {
	new_cache_index = 0;
	new_size = 8192;
	new_rss_limit = ~0UL;
	goto retry_tsb_alloc;
	}

	/* If we failed on a TSB grow, we are under serious
	* memory pressure so don't try to grow any more.
	*/
	if (mm->context.tsb != NULL)
	mm->context.tsb_rss_limit = ~0UL;
	return;
	}

	/* Mark all tags as invalid. */
	tsb_init(new_tsb, new_size);

	/* Ok, we are about to commit the changes. If we are
	* growing an existing TSB the locking is very tricky,
	* so WATCH OUT!
	*
	* We have to hold mm->context.lock while committing to the
	* new TSB, this synchronizes us with processors in
	* flush_tsb_user() and switch_mm() for this address space.
	*
	* But even with that lock held, processors run asynchronously
	* accessing the old TSB via TLB miss handling. This is OK
	* because those actions are just propagating state from the
	* Linux page tables into the TSB, page table mappings are not
	* being changed. If a real fault occurs, the processor will
	* synchronize with us when it hits flush_tsb_user(), this is
	* also true for the case where vmscan is modifying the page
	* tables. The only thing we need to be careful with is to
	* skip any locked TSB entries during copy_tsb().
	*
	* When we finish committing to the new TSB, we have to drop
	* the lock and ask all other cpus running this address space
	* to run tsb_context_switch() to see the new TSB table.
	*/
	spin_lock_irqsave(&mm->context.lock, flags);

	old_tsb = mm->context.tsb;
	old_cache_index = (mm->context.tsb_reg_val & 0x7UL);
	old_size = mm->context.tsb_nentries * sizeof(struct tsb);


	/* Handle multiple threads trying to grow the TSB at the same time.
	* One will get in here first, and bump the size and the RSS limit.
	* The others will get in here next and hit this check.
	*/
	if (unlikely(old_tsb && (rss < mm->context.tsb_rss_limit))) {
	spin_unlock_irqrestore(&mm->context.lock, flags);

	kmem_cache_free(tsb_caches[new_cache_index], new_tsb);
	return;
	}

	mm->context.tsb_rss_limit = new_rss_limit;

	if (old_tsb) {
	extern void copy_tsb(unsigned long old_tsb_base,
	unsigned long old_tsb_size,
	unsigned long new_tsb_base,
	unsigned long new_tsb_size);
	unsigned long old_tsb_base = (unsigned long) old_tsb;
	unsigned long new_tsb_base = (unsigned long) new_tsb;

	if (tlb_type == cheetah_plus \|\| tlb_type == hypervisor) {
	old_tsb_base = __pa(old_tsb_base);
	new_tsb_base = __pa(new_tsb_base);
	}
	copy_tsb(old_tsb_base, old_size, new_tsb_base, new_size);
	}

	mm->context.tsb = new_tsb;
	setup_tsb_params(mm, new_size);

	spin_unlock_irqrestore(&mm->context.lock, flags);

	/* If old_tsb is NULL, we're being invoked for the first time
	* from init_new_context().
	*/
	if (old_tsb) {
	/* Reload it on the local cpu. */
	tsb_context_switch(mm);

	/* Now force other processors to do the same. */
	smp_tsb_sync(mm);

	/* Now it is safe to free the old tsb. */
	kmem_cache_free(tsb_caches[old_cache_index], old_tsb);
	}
	}

	int init_new_context(struct task_struct tsk, struct mm_struct mm)
	{
	spin_lock_init(&mm->context.lock);

	mm->context.sparc64_ctx_val = 0UL;

	/* copy_mm() copies over the parent's mm_struct before calling
	* us, so we need to zero out the TSB pointer or else tsb_grow()
	* will be confused and think there is an older TSB to free up.
	*/
	mm->context.tsb = NULL;

	/* If this is fork, inherit the parent's TSB size. We would
	* grow it to that size on the first page fault anyways.
	*/
	tsb_grow(mm, get_mm_rss(mm));

	if (unlikely(!mm->context.tsb))
	return -ENOMEM;

	return 0;
	}

	void destroy_context(struct mm_struct *mm)
	{
	unsigned long flags, cache_index;

	cache_index = (mm->context.tsb_reg_val & 0x7UL);
	kmem_cache_free(tsb_caches[cache_index], mm->context.tsb);

	/* We can remove these later, but for now it's useful
	* to catch any bogus post-destroy_context() references
	* to the TSB.
	*/
	mm->context.tsb = NULL;
	mm->context.tsb_reg_val = 0UL;

	spin_lock_irqsave(&ctx_alloc_lock, flags);

	if (CTX_VALID(mm->context)) {
	unsigned long nr = CTX_NRBITS(mm->context);
	mmu_context_bmap[nr>>6] &= ~(1UL << (nr & 63));
	}

	spin_unlock_irqrestore(&ctx_alloc_lock, flags);
	}