x86/mm/pat_rbtree.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Handle caching attributes in page tables (PAT)
 *
 * Authors: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *          Suresh B Siddha <suresh.b.siddha@intel.com>
 *
 * 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/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 = rb_entry(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 = rb_entry(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 */
}

enum {
	MEMTYPE_EXACT_MATCH	= 0,
	MEMTYPE_END_MATCH	= 1
};

static struct memtype *memtype_rb_match(struct rb_root *root,
				u64 start, u64 end, int match_type)
{
	struct memtype *match;

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

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

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

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

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

static int memtype_rb_check_conflict(struct rb_root *root,
				u64 start, u64 end,
				enum page_cache_mode reqtype,
				enum page_cache_mode *newtype)
{
	struct rb_node *node;
	struct memtype *match;
	enum page_cache_mode 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 = rb_entry(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:
	pr_info("x86/PAT: %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 = rb_entry(*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,
			     enum page_cache_mode *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;

	/*
	 * Since the memtype_rbroot tree allows overlapping ranges,
	 * rbt_memtype_erase() checks with EXACT_MATCH first, i.e. free
	 * a whole node for the munmap case.  If no such entry is found,
	 * it then checks with END_MATCH, i.e. shrink the size of a node
	 * from the end for the mremap case.
	 */
	data = memtype_rb_match(&memtype_rbroot, start, end,
				MEMTYPE_EXACT_MATCH);
	if (!data) {
		data = memtype_rb_match(&memtype_rbroot, start, end,
					MEMTYPE_END_MATCH);
		if (!data)
			return ERR_PTR(-EINVAL);
	}

	if (data->start == start) {
		/* munmap: erase this node */
		rb_erase_augmented(&data->rb, &memtype_rbroot,
					&memtype_rb_augment_cb);
	} else {
		/* mremap: update the end value of this node */
		rb_erase_augmented(&data->rb, &memtype_rbroot,
					&memtype_rb_augment_cb);
		data->end = start;
		data->subtree_max_end = data->end;
		memtype_rb_insert(&memtype_rbroot, data);
		return NULL;
	}

	return data;
}

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

#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 = rb_entry(node, struct memtype, rb);
		*out = *this;
		return 0;
	} else {
		return 1;
	}
}
#endif