pat_rbtree.c

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/*
 * Handle caching attributes in page tables (PAT)
 *
 * Authors: Venkatesh Pallipadi <[email protected]>
 *          Suresh B Siddha <[email protected]>
 *
 * Interval tree (augmented rbtree) used to store the PAT memory type
 * reservations.
 */

#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/rbtree_augmented.h>
#include <linux/sched.h>
#include <linux/gfp.h>

#include <asm/pgtable.h>
#include <asm/pat.h>

#include "pat_internal.h"

/*
 * The memtype tree keeps track of memory type for specific
 * physical memory areas. Without proper tracking, conflicting memory
 * types in different mappings can cause CPU cache corruption.
 *
 * The tree is an interval tree (augmented rbtree) with tree ordered
 * on starting address. Tree can contain multiple entries for
 * different regions which overlap. All the aliases have the same
 * cache attributes of course.
 *
 * memtype_lock protects the rbtree.
 */

static struct rb_root memtype_rbroot = RB_ROOT;

static int is_node_overlap(struct memtype *node, u64 start, u64 end)
{
    if (node->start >= end || node->end <= start)
        return 0;

    return 1;
}

static u64 get_subtree_max_end(struct rb_node *node)
{
    u64 ret = 0;
    if (node) {
        struct memtype *data = container_of(node, struct memtype, rb);
        ret = data->subtree_max_end;
    }
    return ret;
}

static u64 compute_subtree_max_end(struct memtype *data)
{
    u64 max_end = data->end, child_max_end;

    child_max_end = get_subtree_max_end(data->rb.rb_right);
    if (child_max_end > max_end)
        max_end = child_max_end;

    child_max_end = get_subtree_max_end(data->rb.rb_left);
    if (child_max_end > max_end)
        max_end = child_max_end;

    return max_end;
}

RB_DECLARE_CALLBACKS(static, memtype_rb_augment_cb, struct memtype, rb,
             u64, subtree_max_end, compute_subtree_max_end)

/* Find the first (lowest start addr) overlapping range from rb tree */
static struct memtype *memtype_rb_lowest_match(struct rb_root *root,
                u64 start, u64 end)
{
    struct rb_node *node = root->rb_node;
    struct memtype *last_lower = NULL;

    while (node) {
        struct memtype *data = container_of(node, struct memtype, rb);

        if (get_subtree_max_end(node->rb_left) > start) {
            /* Lowest overlap if any must be on left side */
            node = node->rb_left;
        } else if (is_node_overlap(data, start, end)) {
            last_lower = data;
            break;
        } else if (start >= data->start) {
            /* Lowest overlap if any must be on right side */
            node = node->rb_right;
        } else {
            break;
        }
    }
    return last_lower; /* Returns NULL if there is no overlap */
}

static struct memtype *memtype_rb_exact_match(struct rb_root *root,
                u64 start, u64 end)
{
    struct memtype *match;

    match = memtype_rb_lowest_match(root, start, end);
    while (match != NULL && match->start < end) {
        struct rb_node *node;

        if (match->start == start && match->end == end)
            return match;

        node = rb_next(&match->rb);
        if (node)
            match = container_of(node, struct memtype, rb);
        else
            match = NULL;
    }

    return NULL; /* Returns NULL if there is no exact match */
}

static int memtype_rb_check_conflict(struct rb_root *root,
                u64 start, u64 end,
                unsigned long reqtype, unsigned long *newtype)
{
    struct rb_node *node;
    struct memtype *match;
    int found_type = reqtype;

    match = memtype_rb_lowest_match(&memtype_rbroot, start, end);
    if (match == NULL)
        goto success;

    if (match->type != found_type && newtype == NULL)
        goto failure;

    dprintk("Overlap at 0x%Lx-0x%Lx\n", match->start, match->end);
    found_type = match->type;

    node = rb_next(&match->rb);
    while (node) {
        match = container_of(node, struct memtype, rb);

        if (match->start >= end) /* Checked all possible matches */
            goto success;

        if (is_node_overlap(match, start, end) &&
            match->type != found_type) {
            goto failure;
        }

        node = rb_next(&match->rb);
    }
success:
    if (newtype)
        *newtype = found_type;

    return 0;

failure:
    printk(KERN_INFO "%s:%d conflicting memory types "
        "%Lx-%Lx %s<->%s\n", current->comm, current->pid, start,
        end, cattr_name(found_type), cattr_name(match->type));
    return -EBUSY;
}

static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
{
    struct rb_node **node = &(root->rb_node);
    struct rb_node *parent = NULL;

    while (*node) {
        struct memtype *data = container_of(*node, struct memtype, rb);

        parent = *node;
        if (data->subtree_max_end < newdata->end)
            data->subtree_max_end = newdata->end;
        if (newdata->start <= data->start)
            node = &((*node)->rb_left);
        else if (newdata->start > data->start)
            node = &((*node)->rb_right);
    }

    newdata->subtree_max_end = newdata->end;
    rb_link_node(&newdata->rb, parent, node);
    rb_insert_augmented(&newdata->rb, root, &memtype_rb_augment_cb);
}

int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
{
    int err = 0;

    err = memtype_rb_check_conflict(&memtype_rbroot, new->start, new->end,
                        new->type, ret_type);

    if (!err) {
        if (ret_type)
            new->type = *ret_type;

        new->subtree_max_end = new->end;
        memtype_rb_insert(&memtype_rbroot, new);
    }
    return err;
}

struct memtype *rbt_memtype_erase(u64 start, u64 end)
{
    struct memtype *data;

    data = memtype_rb_exact_match(&memtype_rbroot, start, end);
    if (!data)
        goto out;

    rb_erase_augmented(&data->rb, &memtype_rbroot, &memtype_rb_augment_cb);
out:
    return data;
}

struct memtype *rbt_memtype_lookup(u64 addr)
{
    struct memtype *data;
    data = memtype_rb_lowest_match(&memtype_rbroot, addr, addr + PAGE_SIZE);
    return data;
}

#if defined(CONFIG_DEBUG_FS)
int rbt_memtype_copy_nth_element(struct memtype *out, loff_t pos)
{
    struct rb_node *node;
    int i = 1;

    node = rb_first(&memtype_rbroot);
    while (node && pos != i) {
        node = rb_next(node);
        i++;
    }

    if (node) { /* pos == i */
        struct memtype *this = container_of(node, struct memtype, rb);
        *out = *this;
        return 0;
    } else {
        return 1;
    }
}
#endif