/* SPDX-License-Identifier: GPL-2.0
 *
 * page_pool.c
 *      Author: Jesper Dangaard Brouer <netoptimizer@brouer.com>
 *      Copyright (C) 2016 Red Hat, Inc.
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/slab.h>

#include <net/page_pool.h>
#include <linux/dma-direction.h>
#include <linux/dma-mapping.h>
#include <linux/page-flags.h>
#include <linux/mm.h> /* for __put_page() */

static int page_pool_init(struct page_pool *pool,
                          const struct page_pool_params *params)
{
        unsigned int ring_qsize = 1024; /* Default */

        memcpy(&pool->p, params, sizeof(pool->p));

        /* Validate only known flags were used */
        if (pool->p.flags & ~(PP_FLAG_ALL))
                return -EINVAL;

        if (pool->p.pool_size)
                ring_qsize = pool->p.pool_size;

        /* Sanity limit mem that can be pinned down */
        if (ring_qsize > 32768)
                return -E2BIG;

        /* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
         * DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
         * which is the XDP_TX use-case.
         */
        if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
            (pool->p.dma_dir != DMA_BIDIRECTIONAL))
                return -EINVAL;

        if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
                return -ENOMEM;

        return 0;
}

struct page_pool *page_pool_create(const struct page_pool_params *params)
{
        struct page_pool *pool;
        int err = 0;

        pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
        if (!pool)
                return ERR_PTR(-ENOMEM);

        err = page_pool_init(pool, params);
        if (err < 0) {
                pr_warn("%s() gave up with errno %d\n", __func__, err);
                kfree(pool);
                return ERR_PTR(err);
        }
        return pool;
}
EXPORT_SYMBOL(page_pool_create);

/* fast path */
static struct page *__page_pool_get_cached(struct page_pool *pool)
{
        struct ptr_ring *r = &pool->ring;
        struct page *page;

        /* Quicker fallback, avoid locks when ring is empty */
        if (__ptr_ring_empty(r))
                return NULL;

        /* Test for safe-context, caller should provide this guarantee */
        if (likely(in_serving_softirq())) {
                if (likely(pool->alloc.count)) {
                        /* Fast-path */
                        page = pool->alloc.cache[--pool->alloc.count];
                        return page;
                }
                /* Slower-path: Alloc array empty, time to refill
                 *
                 * Open-coded bulk ptr_ring consumer.
                 *
                 * Discussion: the ring consumer lock is not really
                 * needed due to the softirq/NAPI protection, but
                 * later need the ability to reclaim pages on the
                 * ring. Thus, keeping the locks.
                 */
                spin_lock(&r->consumer_lock);
                while ((page = __ptr_ring_consume(r))) {
                        if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
                                break;
                        pool->alloc.cache[pool->alloc.count++] = page;
                }
                spin_unlock(&r->consumer_lock);
                return page;
        }

        /* Slow-path: Get page from locked ring queue */
        page = ptr_ring_consume(&pool->ring);
        return page;
}

/* slow path */
noinline
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
                                                 gfp_t _gfp)
{
        struct page *page;
        gfp_t gfp = _gfp;
        dma_addr_t dma;

        /* We could always set __GFP_COMP, and avoid this branch, as
         * prep_new_page() can handle order-0 with __GFP_COMP.
         */
        if (pool->p.order)
                gfp |= __GFP_COMP;

        /* FUTURE development:
         *
         * Current slow-path essentially falls back to single page
         * allocations, which doesn't improve performance.  This code
         * need bulk allocation support from the page allocator code.
         */

        /* Cache was empty, do real allocation */
        page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
        if (!page)
                return NULL;

        if (!(pool->p.flags & PP_FLAG_DMA_MAP))
                goto skip_dma_map;

        /* Setup DMA mapping: use 'struct page' area for storing DMA-addr
         * since dma_addr_t can be either 32 or 64 bits and does not always fit
         * into page private data (i.e 32bit cpu with 64bit DMA caps)
         * This mapping is kept for lifetime of page, until leaving pool.
         */
        dma = dma_map_page_attrs(pool->p.dev, page, 0,
                                 (PAGE_SIZE << pool->p.order),
                                 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
        if (dma_mapping_error(pool->p.dev, dma)) {
                put_page(page);
                return NULL;
        }
        page->dma_addr = dma;

skip_dma_map:
        /* When page just alloc'ed is should/must have refcnt 1. */
        return page;
}

/* For using page_pool replace: alloc_pages() API calls, but provide
 * synchronization guarantee for allocation side.
 */
struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
{
        struct page *page;

        /* Fast-path: Get a page from cache */
        page = __page_pool_get_cached(pool);
        if (page)
                return page;

        /* Slow-path: cache empty, do real allocation */
        page = __page_pool_alloc_pages_slow(pool, gfp);
        return page;
}
EXPORT_SYMBOL(page_pool_alloc_pages);

/* Cleanup page_pool state from page */
static void __page_pool_clean_page(struct page_pool *pool,
                                   struct page *page)
{
        dma_addr_t dma;

        if (!(pool->p.flags & PP_FLAG_DMA_MAP))
                return;

        dma = page->dma_addr;
        /* DMA unmap */
        dma_unmap_page_attrs(pool->p.dev, dma,
                             PAGE_SIZE << pool->p.order, pool->p.dma_dir,
                             DMA_ATTR_SKIP_CPU_SYNC);
        page->dma_addr = 0;
}

/* Return a page to the page allocator, cleaning up our state */
static void __page_pool_return_page(struct page_pool *pool, struct page *page)
{
        __page_pool_clean_page(pool, page);
        put_page(page);
        /* An optimization would be to call __free_pages(page, pool->p.order)
         * knowing page is not part of page-cache (thus avoiding a
         * __page_cache_release() call).
         */
}

static bool __page_pool_recycle_into_ring(struct page_pool *pool,
                                   struct page *page)
{
        int ret;
        /* BH protection not needed if current is serving softirq */
        if (in_serving_softirq())
                ret = ptr_ring_produce(&pool->ring, page);
        else
                ret = ptr_ring_produce_bh(&pool->ring, page);

        return (ret == 0) ? true : false;
}

/* Only allow direct recycling in special circumstances, into the
 * alloc side cache.  E.g. during RX-NAPI processing for XDP_DROP use-case.
 *
 * Caller must provide appropriate safe context.
 */
static bool __page_pool_recycle_direct(struct page *page,
                                       struct page_pool *pool)
{
        if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
                return false;

        /* Caller MUST have verified/know (page_ref_count(page) == 1) */
        pool->alloc.cache[pool->alloc.count++] = page;
        return true;
}

void __page_pool_put_page(struct page_pool *pool,
                          struct page *page, bool allow_direct)
{
        /* This allocator is optimized for the XDP mode that uses
         * one-frame-per-page, but have fallbacks that act like the
         * regular page allocator APIs.
         *
         * refcnt == 1 means page_pool owns page, and can recycle it.
         */
        if (likely(page_ref_count(page) == 1)) {
                /* Read barrier done in page_ref_count / READ_ONCE */

                if (allow_direct && in_serving_softirq())
                        if (__page_pool_recycle_direct(page, pool))
                                return;

                if (!__page_pool_recycle_into_ring(pool, page)) {
                        /* Cache full, fallback to free pages */
                        __page_pool_return_page(pool, page);
                }
                return;
        }
        /* Fallback/non-XDP mode: API user have elevated refcnt.
         *
         * Many drivers split up the page into fragments, and some
         * want to keep doing this to save memory and do refcnt based
         * recycling. Support this use case too, to ease drivers
         * switching between XDP/non-XDP.
         *
         * In-case page_pool maintains the DMA mapping, API user must
         * call page_pool_put_page once.  In this elevated refcnt
         * case, the DMA is unmapped/released, as driver is likely
         * doing refcnt based recycle tricks, meaning another process
         * will be invoking put_page.
         */
        __page_pool_clean_page(pool, page);
        put_page(page);
}
EXPORT_SYMBOL(__page_pool_put_page);

static void __page_pool_empty_ring(struct page_pool *pool)
{
        struct page *page;

        /* Empty recycle ring */
        while ((page = ptr_ring_consume_bh(&pool->ring))) {
                /* Verify the refcnt invariant of cached pages */
                if (!(page_ref_count(page) == 1))
                        pr_crit("%s() page_pool refcnt %d violation\n",
                                __func__, page_ref_count(page));

                __page_pool_return_page(pool, page);
        }
}

static void __page_pool_destroy_rcu(struct rcu_head *rcu)
{
        struct page_pool *pool;

        pool = container_of(rcu, struct page_pool, rcu);

        WARN(pool->alloc.count, "API usage violation");

        __page_pool_empty_ring(pool);
        ptr_ring_cleanup(&pool->ring, NULL);
        kfree(pool);
}

/* Cleanup and release resources */
void page_pool_destroy(struct page_pool *pool)
{
        struct page *page;

        /* Empty alloc cache, assume caller made sure this is
         * no-longer in use, and page_pool_alloc_pages() cannot be
         * call concurrently.
         */
        while (pool->alloc.count) {
                page = pool->alloc.cache[--pool->alloc.count];
                __page_pool_return_page(pool, page);
        }

        /* No more consumers should exist, but producers could still
         * be in-flight.
         */
        __page_pool_empty_ring(pool);

        /* An xdp_mem_allocator can still ref page_pool pointer */
        call_rcu(&pool->rcu, __page_pool_destroy_rcu);
}
EXPORT_SYMBOL(page_pool_destroy);