tlb.c

Go to the documentation of this file.

#include <linux/init.h>

#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/cpu.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/cache.h>
#include <asm/apic.h>
#include <asm/uv/uv.h>
#include <linux/debugfs.h>

DEFINE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate)
            = { &init_mm, 0, };

/*
 *  Smarter SMP flushing macros.
 *      c/o Linus Torvalds.
 *
 *  These mean you can really definitely utterly forget about
 *  writing to user space from interrupts. (Its not allowed anyway).
 *
 *  Optimizations Manfred Spraul <[email protected]>
 *
 *  More scalable flush, from Andi Kleen
 *
 *  Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
 */

struct flush_tlb_info {
    struct mm_struct *flush_mm;
    unsigned long flush_start;
    unsigned long flush_end;
};

/*
 * We cannot call mmdrop() because we are in interrupt context,
 * instead update mm->cpu_vm_mask.
 */
void leave_mm(int cpu)
{
    struct mm_struct *active_mm = this_cpu_read(cpu_tlbstate.active_mm);
    if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
        BUG();
    if (cpumask_test_cpu(cpu, mm_cpumask(active_mm))) {
        cpumask_clear_cpu(cpu, mm_cpumask(active_mm));
        load_cr3(swapper_pg_dir);
    }
}
EXPORT_SYMBOL_GPL(leave_mm);

/*
 * The flush IPI assumes that a thread switch happens in this order:
 * [cpu0: the cpu that switches]
 * 1) switch_mm() either 1a) or 1b)
 * 1a) thread switch to a different mm
 * 1a1) set cpu_tlbstate to TLBSTATE_OK
 *  Now the tlb flush NMI handler flush_tlb_func won't call leave_mm
 *  if cpu0 was in lazy tlb mode.
 * 1a2) update cpu active_mm
 *  Now cpu0 accepts tlb flushes for the new mm.
 * 1a3) cpu_set(cpu, new_mm->cpu_vm_mask);
 *  Now the other cpus will send tlb flush ipis.
 * 1a4) change cr3.
 * 1a5) cpu_clear(cpu, old_mm->cpu_vm_mask);
 *  Stop ipi delivery for the old mm. This is not synchronized with
 *  the other cpus, but flush_tlb_func ignore flush ipis for the wrong
 *  mm, and in the worst case we perform a superfluous tlb flush.
 * 1b) thread switch without mm change
 *  cpu active_mm is correct, cpu0 already handles flush ipis.
 * 1b1) set cpu_tlbstate to TLBSTATE_OK
 * 1b2) test_and_set the cpu bit in cpu_vm_mask.
 *  Atomically set the bit [other cpus will start sending flush ipis],
 *  and test the bit.
 * 1b3) if the bit was 0: leave_mm was called, flush the tlb.
 * 2) switch %%esp, ie current
 *
 * The interrupt must handle 2 special cases:
 * - cr3 is changed before %%esp, ie. it cannot use current->{active_,}mm.
 * - the cpu performs speculative tlb reads, i.e. even if the cpu only
 *   runs in kernel space, the cpu could load tlb entries for user space
 *   pages.
 *
 * The good news is that cpu_tlbstate is local to each cpu, no
 * write/read ordering problems.
 */

/*
 * TLB flush funcation:
 * 1) Flush the tlb entries if the cpu uses the mm that's being flushed.
 * 2) Leave the mm if we are in the lazy tlb mode.
 */
static void flush_tlb_func(void *info)
{
    struct flush_tlb_info *f = info;

    inc_irq_stat(irq_tlb_count);

    if (f->flush_mm != this_cpu_read(cpu_tlbstate.active_mm))
        return;

    if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
        if (f->flush_end == TLB_FLUSH_ALL || !cpu_has_invlpg)
            local_flush_tlb();
        else if (!f->flush_end)
            __flush_tlb_single(f->flush_start);
        else {
            unsigned long addr;
            addr = f->flush_start;
            while (addr < f->flush_end) {
                __flush_tlb_single(addr);
                addr += PAGE_SIZE;
            }
        }
    } else
        leave_mm(smp_processor_id());

}

void native_flush_tlb_others(const struct cpumask *cpumask,
                 struct mm_struct *mm, unsigned long start,
                 unsigned long end)
{
    struct flush_tlb_info info;
    info.flush_mm = mm;
    info.flush_start = start;
    info.flush_end = end;

    if (is_uv_system()) {
        unsigned int cpu;

        cpu = smp_processor_id();
        cpumask = uv_flush_tlb_others(cpumask, mm, start, end, cpu);
        if (cpumask)
            smp_call_function_many(cpumask, flush_tlb_func,
                                &info, 1);
        return;
    }
    smp_call_function_many(cpumask, flush_tlb_func, &info, 1);
}

void flush_tlb_current_task(void)
{
    struct mm_struct *mm = current->mm;

    preempt_disable();

    local_flush_tlb();
    if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
        flush_tlb_others(mm_cpumask(mm), mm, 0UL, TLB_FLUSH_ALL);
    preempt_enable();
}

/*
 * It can find out the THP large page, or
 * HUGETLB page in tlb_flush when THP disabled
 */
static inline unsigned long has_large_page(struct mm_struct *mm,
                 unsigned long start, unsigned long end)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    unsigned long addr = ALIGN(start, HPAGE_SIZE);
    for (; addr < end; addr += HPAGE_SIZE) {
        pgd = pgd_offset(mm, addr);
        if (likely(!pgd_none(*pgd))) {
            pud = pud_offset(pgd, addr);
            if (likely(!pud_none(*pud))) {
                pmd = pmd_offset(pud, addr);
                if (likely(!pmd_none(*pmd)))
                    if (pmd_large(*pmd))
                        return addr;
            }
        }
    }
    return 0;
}

void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
                unsigned long end, unsigned long vmflag)
{
    unsigned long addr;
    unsigned act_entries, tlb_entries = 0;

    preempt_disable();
    if (current->active_mm != mm)
        goto flush_all;

    if (!current->mm) {
        leave_mm(smp_processor_id());
        goto flush_all;
    }

    if (end == TLB_FLUSH_ALL || tlb_flushall_shift == -1
                    || vmflag & VM_HUGETLB) {
        local_flush_tlb();
        goto flush_all;
    }

    /* In modern CPU, last level tlb used for both data/ins */
    if (vmflag & VM_EXEC)
        tlb_entries = tlb_lli_4k[ENTRIES];
    else
        tlb_entries = tlb_lld_4k[ENTRIES];
    /* Assume all of TLB entries was occupied by this task */
    act_entries = mm->total_vm > tlb_entries ? tlb_entries : mm->total_vm;

    /* tlb_flushall_shift is on balance point, details in commit log */
    if ((end - start) >> PAGE_SHIFT > act_entries >> tlb_flushall_shift)
        local_flush_tlb();
    else {
        if (has_large_page(mm, start, end)) {
            local_flush_tlb();
            goto flush_all;
        }
        /* flush range by one by one 'invlpg' */
        for (addr = start; addr < end;  addr += PAGE_SIZE)
            __flush_tlb_single(addr);

        if (cpumask_any_but(mm_cpumask(mm),
                smp_processor_id()) < nr_cpu_ids)
            flush_tlb_others(mm_cpumask(mm), mm, start, end);
        preempt_enable();
        return;
    }

flush_all:
    if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
        flush_tlb_others(mm_cpumask(mm), mm, 0UL, TLB_FLUSH_ALL);
    preempt_enable();
}

void flush_tlb_page(struct vm_area_struct *vma, unsigned long start)
{
    struct mm_struct *mm = vma->vm_mm;

    preempt_disable();

    if (current->active_mm == mm) {
        if (current->mm)
            __flush_tlb_one(start);
        else
            leave_mm(smp_processor_id());
    }

    if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
        flush_tlb_others(mm_cpumask(mm), mm, start, 0UL);

    preempt_enable();
}

static void do_flush_tlb_all(void *info)
{
    __flush_tlb_all();
    if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
        leave_mm(smp_processor_id());
}

void flush_tlb_all(void)
{
    on_each_cpu(do_flush_tlb_all, NULL, 1);
}

static void do_kernel_range_flush(void *info)
{
    struct flush_tlb_info *f = info;
    unsigned long addr;

    /* flush range by one by one 'invlpg' */
    for (addr = f->flush_start; addr < f->flush_end; addr += PAGE_SIZE)
        __flush_tlb_single(addr);
}

void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{
    unsigned act_entries;
    struct flush_tlb_info info;

    /* In modern CPU, last level tlb used for both data/ins */
    act_entries = tlb_lld_4k[ENTRIES];

    /* Balance as user space task's flush, a bit conservative */
    if (end == TLB_FLUSH_ALL || tlb_flushall_shift == -1 ||
        (end - start) >> PAGE_SHIFT > act_entries >> tlb_flushall_shift)

        on_each_cpu(do_flush_tlb_all, NULL, 1);
    else {
        info.flush_start = start;
        info.flush_end = end;
        on_each_cpu(do_kernel_range_flush, &info, 1);
    }
}

#ifdef CONFIG_DEBUG_TLBFLUSH
static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
                 size_t count, loff_t *ppos)
{
    char buf[32];
    unsigned int len;

    len = sprintf(buf, "%hd\n", tlb_flushall_shift);
    return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

static ssize_t tlbflush_write_file(struct file *file,
         const char __user *user_buf, size_t count, loff_t *ppos)
{
    char buf[32];
    ssize_t len;
    s8 shift;

    len = min(count, sizeof(buf) - 1);
    if (copy_from_user(buf, user_buf, len))
        return -EFAULT;

    buf[len] = '\0';
    if (kstrtos8(buf, 0, &shift))
        return -EINVAL;

    if (shift < -1 || shift >= BITS_PER_LONG)
        return -EINVAL;

    tlb_flushall_shift = shift;
    return count;
}

static const struct file_operations fops_tlbflush = {
    .read = tlbflush_read_file,
    .write = tlbflush_write_file,
    .llseek = default_llseek,
};

static int __cpuinit create_tlb_flushall_shift(void)
{
    if (cpu_has_invlpg) {
        debugfs_create_file("tlb_flushall_shift", S_IRUSR | S_IWUSR,
            arch_debugfs_dir, NULL, &fops_tlbflush);
    }
    return 0;
}
late_initcall(create_tlb_flushall_shift);
#endif