page_alloc.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2020 Google LLC
 * Author: Quentin Perret <qperret@google.com>
 */
 
#include <asm/kvm_hyp.h>
#include <nvhe/gfp.h>
 
u64 __hyp_vmemmap;
 
/*
 * Index the hyp_vmemmap to find a potential buddy page, but make no assumption
 * about its current state.
 *
 * Example buddy-tree for a 4-pages physically contiguous pool:
 *
 *                 o : Page 3
 *                /
 *               o-o : Page 2
 *              /
 *             /   o : Page 1
 *            /   /
 *           o---o-o : Page 0
 *    Order  2   1 0
 *
 * Example of requests on this pool:
 *   __find_buddy_nocheck(pool, page 0, order 0) => page 1
 *   __find_buddy_nocheck(pool, page 0, order 1) => page 2
 *   __find_buddy_nocheck(pool, page 1, order 0) => page 0
 *   __find_buddy_nocheck(pool, page 2, order 0) => page 3
 */
static struct hyp_page *__find_buddy_nocheck(struct hyp_pool *pool,
                         struct hyp_page *p,
                         unsigned short order)
{
    phys_addr_t addr = hyp_page_to_phys(p);
 
    addr ^= (PAGE_SIZE << order);
 
    /*
     * Don't return a page outside the pool range -- it belongs to
     * something else and may not be mapped in hyp_vmemmap.
     */
    if (addr < pool->range_start || addr >= pool->range_end)
        return NULL;
 
    return hyp_phys_to_page(addr);
}
 
/* Find a buddy page currently available for allocation */
static struct hyp_page *__find_buddy_avail(struct hyp_pool *pool,
                       struct hyp_page *p,
                       unsigned short order)
{
    struct hyp_page *buddy = __find_buddy_nocheck(pool, p, order);
 
    if (!buddy || buddy->order != order || buddy->refcount)
        return NULL;
 
    return buddy;
 
}
 
/*
 * Pages that are available for allocation are tracked in free-lists, so we use
 * the pages themselves to store the list nodes to avoid wasting space. As the
 * allocator always returns zeroed pages (which are zeroed on the hyp_put_page()
 * path to optimize allocation speed), we also need to clean-up the list node in
 * each page when we take it out of the list.
 */
static inline void page_remove_from_list(struct hyp_page *p)
{
    struct list_head *node = hyp_page_to_virt(p);
 
    __list_del_entry(node);
    memset(node, 0, sizeof(*node));
}
 
static inline void page_add_to_list(struct hyp_page *p, struct list_head *head)
{
    struct list_head *node = hyp_page_to_virt(p);
 
    INIT_LIST_HEAD(node);
    list_add_tail(node, head);
}
 
static inline struct hyp_page *node_to_page(struct list_head *node)
{
    return hyp_virt_to_page(node);
}
 
static void __hyp_attach_page(struct hyp_pool *pool,
                  struct hyp_page *p)
{
    phys_addr_t phys = hyp_page_to_phys(p);
    unsigned short order = p->order;
    struct hyp_page *buddy;
 
    memset(hyp_page_to_virt(p), 0, PAGE_SIZE << p->order);
 
    /* Skip coalescing for 'external' pages being freed into the pool. */
    if (phys < pool->range_start || phys >= pool->range_end)
        goto insert;
 
    /*
     * Only the first struct hyp_page of a high-order page (otherwise known
     * as the 'head') should have p->order set. The non-head pages should
     * have p->order = HYP_NO_ORDER. Here @p may no longer be the head
     * after coalescing, so make sure to mark it HYP_NO_ORDER proactively.
     */
    p->order = HYP_NO_ORDER;
    for (; (order + 1) <= pool->max_order; order++) {
        buddy = __find_buddy_avail(pool, p, order);
        if (!buddy)
            break;
 
        /* Take the buddy out of its list, and coalesce with @p */
        page_remove_from_list(buddy);
        buddy->order = HYP_NO_ORDER;
        p = min(p, buddy);
    }
 
insert:
    /* Mark the new head, and insert it */
    p->order = order;
    page_add_to_list(p, &pool->free_area[order]);
}
 
static struct hyp_page *__hyp_extract_page(struct hyp_pool *pool,
                       struct hyp_page *p,
                       unsigned short order)
{
    struct hyp_page *buddy;
 
    page_remove_from_list(p);
    while (p->order > order) {
        /*
         * The buddy of order n - 1 currently has HYP_NO_ORDER as it
         * is covered by a higher-level page (whose head is @p). Use
         * __find_buddy_nocheck() to find it and inject it in the
         * free_list[n - 1], effectively splitting @p in half.
         */
        p->order--;
        buddy = __find_buddy_nocheck(pool, p, p->order);
        buddy->order = p->order;
        page_add_to_list(buddy, &pool->free_area[buddy->order]);
    }
 
    return p;
}
 
static void __hyp_put_page(struct hyp_pool *pool, struct hyp_page *p)
{
    if (hyp_page_ref_dec_and_test(p))
        __hyp_attach_page(pool, p);
}
 
/*
 * Changes to the buddy tree and page refcounts must be done with the hyp_pool
 * lock held. If a refcount change requires an update to the buddy tree (e.g.
 * hyp_put_page()), both operations must be done within the same critical
 * section to guarantee transient states (e.g. a page with null refcount but
 * not yet attached to a free list) can't be observed by well-behaved readers.
 */
void hyp_put_page(struct hyp_pool *pool, void *addr)
{
    struct hyp_page *p = hyp_virt_to_page(addr);
 
    hyp_spin_lock(&pool->lock);
    __hyp_put_page(pool, p);
    hyp_spin_unlock(&pool->lock);
}
 
void hyp_get_page(struct hyp_pool *pool, void *addr)
{
    struct hyp_page *p = hyp_virt_to_page(addr);
 
    hyp_spin_lock(&pool->lock);
    hyp_page_ref_inc(p);
    hyp_spin_unlock(&pool->lock);
}
 
void hyp_split_page(struct hyp_page *p)
{
    unsigned short order = p->order;
    unsigned int i;
 
    p->order = 0;
    for (i = 1; i < (1 << order); i++) {
        struct hyp_page *tail = p + i;
 
        tail->order = 0;
        hyp_set_page_refcounted(tail);
    }
}
 
void *hyp_alloc_pages(struct hyp_pool *pool, unsigned short order)
{
    unsigned short i = order;
    struct hyp_page *p;
 
    hyp_spin_lock(&pool->lock);
 
    /* Look for a high-enough-order page */
    while (i <= pool->max_order && list_empty(&pool->free_area[i]))
        i++;
    if (i > pool->max_order) {
        hyp_spin_unlock(&pool->lock);
        return NULL;
    }
 
    /* Extract it from the tree at the right order */
    p = node_to_page(pool->free_area[i].next);
    p = __hyp_extract_page(pool, p, order);
 
    hyp_set_page_refcounted(p);
    hyp_spin_unlock(&pool->lock);
 
    return hyp_page_to_virt(p);
}
 
int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
          unsigned int reserved_pages)
{
    phys_addr_t phys = hyp_pfn_to_phys(pfn);
    struct hyp_page *p;
    int i;
 
    hyp_spin_lock_init(&pool->lock);
    pool->max_order = min(MAX_PAGE_ORDER,
                  get_order(nr_pages << PAGE_SHIFT));
    for (i = 0; i <= pool->max_order; i++)
        INIT_LIST_HEAD(&pool->free_area[i]);
    pool->range_start = phys;
    pool->range_end = phys + (nr_pages << PAGE_SHIFT);
 
    /* Init the vmemmap portion */
    p = hyp_phys_to_page(phys);
    for (i = 0; i < nr_pages; i++)
        hyp_set_page_refcounted(&p[i]);
 
    /* Attach the unused pages to the buddy tree */
    for (i = reserved_pages; i < nr_pages; i++)
        __hyp_put_page(pool, &p[i]);
 
    return 0;
}