tegrakernel/kernel/kernel-4.9/arch/tile/include/asm/mmu_context.h

/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#ifndef _ASM_TILE_MMU_CONTEXT_H
#define _ASM_TILE_MMU_CONTEXT_H

#include <linux/smp.h>
#include <asm/setup.h>
#include <asm/page.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/homecache.h>
#include <asm-generic/mm_hooks.h>

static inline int
init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
	return 0;
}

/*
 * Note that arch/tile/kernel/head_NN.S and arch/tile/mm/migrate_NN.S
 * also call hv_install_context().
 */
static inline void __install_page_table(pgd_t *pgdir, int asid, pgprot_t prot)
{
	/* FIXME: DIRECTIO should not always be set. FIXME. */
	int rc = hv_install_context(__pa(pgdir), prot, asid,
				    HV_CTX_DIRECTIO | CTX_PAGE_FLAG);
	if (rc < 0)
		panic("hv_install_context failed: %d", rc);
}

static inline void install_page_table(pgd_t *pgdir, int asid)
{
	pte_t *ptep = virt_to_kpte((unsigned long)pgdir);
	__install_page_table(pgdir, asid, *ptep);
}

/*
 * "Lazy" TLB mode is entered when we are switching to a kernel task,
 * which borrows the mm of the previous task.  The goal of this
 * optimization is to avoid having to install a new page table.  On
 * early x86 machines (where the concept originated) you couldn't do
 * anything short of a full page table install for invalidation, so
 * handling a remote TLB invalidate required doing a page table
 * re-install.  Someone clearly decided that it was silly to keep
 * doing this while in "lazy" TLB mode, so the optimization involves
 * installing the swapper page table instead the first time one
 * occurs, and clearing the cpu out of cpu_vm_mask, so the cpu running
 * the kernel task doesn't need to take any more interrupts.  At that
 * point it's then necessary to explicitly reinstall it when context
 * switching back to the original mm.
 *
 * On Tile, we have to do a page-table install whenever DMA is enabled,
 * so in that case lazy mode doesn't help anyway.  And more generally,
 * we have efficient per-page TLB shootdown, and don't expect to spend
 * that much time in kernel tasks in general, so just leaving the
 * kernel task borrowing the old page table, but handling TLB
 * shootdowns, is a reasonable thing to do.  And importantly, this
 * lets us use the hypervisor's internal APIs for TLB shootdown, which
 * means we don't have to worry about having TLB shootdowns blocked
 * when Linux is disabling interrupts; see the page migration code for
 * an example of where it's important for TLB shootdowns to complete
 * even when interrupts are disabled at the Linux level.
 */
static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *t)
{
#if CHIP_HAS_TILE_DMA()
	/*
	 * We have to do an "identity" page table switch in order to
	 * clear any pending DMA interrupts.
	 */
	if (current->thread.tile_dma_state.enabled)
		install_page_table(mm->pgd, __this_cpu_read(current_asid));
#endif
}

static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
			     struct task_struct *tsk)
{
	if (likely(prev != next)) {

		int cpu = smp_processor_id();

		/* Pick new ASID. */
		int asid = __this_cpu_read(current_asid) + 1;
		if (asid > max_asid) {
			asid = min_asid;
			local_flush_tlb();
		}
		__this_cpu_write(current_asid, asid);

		/* Clear cpu from the old mm, and set it in the new one. */
		cpumask_clear_cpu(cpu, mm_cpumask(prev));
		cpumask_set_cpu(cpu, mm_cpumask(next));

		/* Re-load page tables */
		install_page_table(next->pgd, asid);

		/* See how we should set the red/black cache info */
		check_mm_caching(prev, next);

		/*
		 * Since we're changing to a new mm, we have to flush
		 * the icache in case some physical page now being mapped
		 * has subsequently been repurposed and has new code.
		 */
		__flush_icache();

	}
}

static inline void activate_mm(struct mm_struct *prev_mm,
			       struct mm_struct *next_mm)
{
	switch_mm(prev_mm, next_mm, NULL);
}

#define destroy_context(mm)		do { } while (0)
#define deactivate_mm(tsk, mm)          do { } while (0)

#endif /* _ASM_TILE_MMU_CONTEXT_H */