1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2020 Google LLC
4 * Author: Quentin Perret <qperret@google.com>
5 */
6
7#include <asm/kvm_hyp.h>
8#include <nvhe/gfp.h>
9
10u64 __hyp_vmemmap;
11
12/*
13 * Index the hyp_vmemmap to find a potential buddy page, but make no assumption
14 * about its current state.
15 *
16 * Example buddy-tree for a 4-pages physically contiguous pool:
17 *
18 *                 o : Page 3
19 *                /
20 *               o-o : Page 2
21 *              /
22 *             /   o : Page 1
23 *            /   /
24 *           o---o-o : Page 0
25 *    Order  2   1 0
26 *
27 * Example of requests on this pool:
28 *   __find_buddy_nocheck(pool, page 0, order 0) => page 1
29 *   __find_buddy_nocheck(pool, page 0, order 1) => page 2
30 *   __find_buddy_nocheck(pool, page 1, order 0) => page 0
31 *   __find_buddy_nocheck(pool, page 2, order 0) => page 3
32 */
33static struct hyp_page *__find_buddy_nocheck(struct hyp_pool *pool,
34					     struct hyp_page *p,
35					     unsigned short order)
36{
37	phys_addr_t addr = hyp_page_to_phys(p);
38
39	addr ^= (PAGE_SIZE << order);
40
41	/*
42	 * Don't return a page outside the pool range -- it belongs to
43	 * something else and may not be mapped in hyp_vmemmap.
44	 */
45	if (addr < pool->range_start || addr >= pool->range_end)
46		return NULL;
47
48	return hyp_phys_to_page(addr);
49}
50
51/* Find a buddy page currently available for allocation */
52static struct hyp_page *__find_buddy_avail(struct hyp_pool *pool,
53					   struct hyp_page *p,
54					   unsigned short order)
55{
56	struct hyp_page *buddy = __find_buddy_nocheck(pool, p, order);
57
58	if (!buddy || buddy->order != order || buddy->refcount)
59		return NULL;
60
61	return buddy;
62
63}
64
65/*
66 * Pages that are available for allocation are tracked in free-lists, so we use
67 * the pages themselves to store the list nodes to avoid wasting space. As the
68 * allocator always returns zeroed pages (which are zeroed on the hyp_put_page()
69 * path to optimize allocation speed), we also need to clean-up the list node in
70 * each page when we take it out of the list.
71 */
72static inline void page_remove_from_list(struct hyp_page *p)
73{
74	struct list_head *node = hyp_page_to_virt(p);
75
76	__list_del_entry(node);
77	memset(node, 0, sizeof(*node));
78}
79
80static inline void page_add_to_list(struct hyp_page *p, struct list_head *head)
81{
82	struct list_head *node = hyp_page_to_virt(p);
83
84	INIT_LIST_HEAD(node);
85	list_add_tail(node, head);
86}
87
88static inline struct hyp_page *node_to_page(struct list_head *node)
89{
90	return hyp_virt_to_page(node);
91}
92
93static void __hyp_attach_page(struct hyp_pool *pool,
94			      struct hyp_page *p)
95{
96	phys_addr_t phys = hyp_page_to_phys(p);
97	unsigned short order = p->order;
98	struct hyp_page *buddy;
99
100	memset(hyp_page_to_virt(p), 0, PAGE_SIZE << p->order);
101
102	/* Skip coalescing for 'external' pages being freed into the pool. */
103	if (phys < pool->range_start || phys >= pool->range_end)
104		goto insert;
105
106	/*
107	 * Only the first struct hyp_page of a high-order page (otherwise known
108	 * as the 'head') should have p->order set. The non-head pages should
109	 * have p->order = HYP_NO_ORDER. Here @p may no longer be the head
110	 * after coalescing, so make sure to mark it HYP_NO_ORDER proactively.
111	 */
112	p->order = HYP_NO_ORDER;
113	for (; (order + 1) <= pool->max_order; order++) {
114		buddy = __find_buddy_avail(pool, p, order);
115		if (!buddy)
116			break;
117
118		/* Take the buddy out of its list, and coalesce with @p */
119		page_remove_from_list(buddy);
120		buddy->order = HYP_NO_ORDER;
121		p = min(p, buddy);
122	}
123
124insert:
125	/* Mark the new head, and insert it */
126	p->order = order;
127	page_add_to_list(p, &pool->free_area[order]);
128}
129
130static struct hyp_page *__hyp_extract_page(struct hyp_pool *pool,
131					   struct hyp_page *p,
132					   unsigned short order)
133{
134	struct hyp_page *buddy;
135
136	page_remove_from_list(p);
137	while (p->order > order) {
138		/*
139		 * The buddy of order n - 1 currently has HYP_NO_ORDER as it
140		 * is covered by a higher-level page (whose head is @p). Use
141		 * __find_buddy_nocheck() to find it and inject it in the
142		 * free_list[n - 1], effectively splitting @p in half.
143		 */
144		p->order--;
145		buddy = __find_buddy_nocheck(pool, p, p->order);
146		buddy->order = p->order;
147		page_add_to_list(buddy, &pool->free_area[buddy->order]);
148	}
149
150	return p;
151}
152
153static void __hyp_put_page(struct hyp_pool *pool, struct hyp_page *p)
154{
155	if (hyp_page_ref_dec_and_test(p))
156		__hyp_attach_page(pool, p);
157}
158
159/*
160 * Changes to the buddy tree and page refcounts must be done with the hyp_pool
161 * lock held. If a refcount change requires an update to the buddy tree (e.g.
162 * hyp_put_page()), both operations must be done within the same critical
163 * section to guarantee transient states (e.g. a page with null refcount but
164 * not yet attached to a free list) can't be observed by well-behaved readers.
165 */
166void hyp_put_page(struct hyp_pool *pool, void *addr)
167{
168	struct hyp_page *p = hyp_virt_to_page(addr);
169
170	hyp_spin_lock(&pool->lock);
171	__hyp_put_page(pool, p);
172	hyp_spin_unlock(&pool->lock);
173}
174
175void hyp_get_page(struct hyp_pool *pool, void *addr)
176{
177	struct hyp_page *p = hyp_virt_to_page(addr);
178
179	hyp_spin_lock(&pool->lock);
180	hyp_page_ref_inc(p);
181	hyp_spin_unlock(&pool->lock);
182}
183
184void hyp_split_page(struct hyp_page *p)
185{
186	unsigned short order = p->order;
187	unsigned int i;
188
189	p->order = 0;
190	for (i = 1; i < (1 << order); i++) {
191		struct hyp_page *tail = p + i;
192
193		tail->order = 0;
194		hyp_set_page_refcounted(tail);
195	}
196}
197
198void *hyp_alloc_pages(struct hyp_pool *pool, unsigned short order)
199{
200	unsigned short i = order;
201	struct hyp_page *p;
202
203	hyp_spin_lock(&pool->lock);
204
205	/* Look for a high-enough-order page */
206	while (i <= pool->max_order && list_empty(&pool->free_area[i]))
207		i++;
208	if (i > pool->max_order) {
209		hyp_spin_unlock(&pool->lock);
210		return NULL;
211	}
212
213	/* Extract it from the tree at the right order */
214	p = node_to_page(pool->free_area[i].next);
215	p = __hyp_extract_page(pool, p, order);
216
217	hyp_set_page_refcounted(p);
218	hyp_spin_unlock(&pool->lock);
219
220	return hyp_page_to_virt(p);
221}
222
223int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
224		  unsigned int reserved_pages)
225{
226	phys_addr_t phys = hyp_pfn_to_phys(pfn);
227	struct hyp_page *p;
228	int i;
229
230	hyp_spin_lock_init(&pool->lock);
231	pool->max_order = min(MAX_ORDER, get_order(nr_pages << PAGE_SHIFT));
232	for (i = 0; i <= pool->max_order; i++)
233		INIT_LIST_HEAD(&pool->free_area[i]);
234	pool->range_start = phys;
235	pool->range_end = phys + (nr_pages << PAGE_SHIFT);
236
237	/* Init the vmemmap portion */
238	p = hyp_phys_to_page(phys);
239	for (i = 0; i < nr_pages; i++)
240		hyp_set_page_refcounted(&p[i]);
241
242	/* Attach the unused pages to the buddy tree */
243	for (i = reserved_pages; i < nr_pages; i++)
244		__hyp_put_page(pool, &p[i]);
245
246	return 0;
247}
248