mmu_context.h
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/*
* 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 */