@@ -6,6 +6,7 @@
#include <linux/dma-direction.h>
#include <linux/ptr_ring.h>
#include <linux/types.h>
+#include <linux/xarray.h>
#include <net/netmem.h>
#define PP_FLAG_DMA_MAP BIT(0) /* Should page_pool do the DMA
@@ -58,13 +59,38 @@ struct pp_alloc_cache {
netmem_ref cache[PP_ALLOC_CACHE_SIZE];
};
+/*
+ * DMA mapping IDs
+ *
+ * When DMA-mapping a page, we allocate an ID (from an xarray) and stash this in
+ * the upper bits of page->pp_magic. The number of bits available here is
+ * constrained by the size of an unsigned long, and the definition of
+ * PP_SIGNATURE.
+ */
+#define PP_DMA_INDEX_SHIFT (1 + __fls(PP_SIGNATURE - POISON_POINTER_DELTA))
+#define _PP_DMA_INDEX_BITS MIN(32, BITS_PER_LONG - PP_DMA_INDEX_SHIFT - 1)
+
+/* PP_SIGNATURE includes POISON_POINTER_DELTA, so limit the size of the DMA
+ * index to not overlap with that if set
+ */
+#if POISON_POINTER_DELTA > 0
+#define PP_DMA_INDEX_BITS MIN(_PP_DMA_INDEX_BITS, \
+ __ffs(POISON_POINTER_DELTA) - PP_DMA_INDEX_SHIFT)
+#else
+#define PP_DMA_INDEX_BITS _PP_DMA_INDEX_BITS
+#endif
+
+#define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \
+ PP_DMA_INDEX_SHIFT)
+#define PP_DMA_INDEX_LIMIT XA_LIMIT(1, BIT(PP_DMA_INDEX_BITS) - 1)
+
/* Mask used for checking in page_pool_page_is_pp() below. page->pp_magic is
* OR'ed with PP_SIGNATURE after the allocation in order to preserve bit 0 for
- * the head page of compound page and bit 1 for pfmemalloc page.
- * page_is_pfmemalloc() is checked in __page_pool_put_page() to avoid recycling
- * the pfmemalloc page.
+ * the head page of compound page and bit 1 for pfmemalloc page, as well as the
+ * bits used for the DMA index. page_is_pfmemalloc() is checked in
+ * __page_pool_put_page() to avoid recycling the pfmemalloc page.
*/
-#define PP_MAGIC_MASK ~0x3UL
+#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
/**
* struct page_pool_params - page pool parameters
@@ -233,6 +259,8 @@ struct page_pool {
void *mp_priv;
const struct memory_provider_ops *mp_ops;
+ struct xarray dma_mapped;
+
#ifdef CONFIG_PAGE_POOL_STATS
/* recycle stats are per-cpu to avoid locking */
struct page_pool_recycle_stats __percpu *recycle_stats;
@@ -5,7 +5,7 @@
static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
{
- return __netmem_clear_lsb(netmem)->pp_magic;
+ return __netmem_clear_lsb(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
}
static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
@@ -15,6 +15,8 @@ static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
static inline void netmem_clear_pp_magic(netmem_ref netmem)
{
+ WARN_ON_ONCE(__netmem_clear_lsb(netmem)->pp_magic & PP_DMA_INDEX_MASK);
+
__netmem_clear_lsb(netmem)->pp_magic = 0;
}
@@ -33,4 +35,28 @@ static inline void netmem_set_dma_addr(netmem_ref netmem,
{
__netmem_clear_lsb(netmem)->dma_addr = dma_addr;
}
+
+static inline unsigned long netmem_get_dma_index(netmem_ref netmem)
+{
+ unsigned long magic;
+
+ if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
+ return 0;
+
+ magic = __netmem_clear_lsb(netmem)->pp_magic;
+
+ return (magic & PP_DMA_INDEX_MASK) >> PP_DMA_INDEX_SHIFT;
+}
+
+static inline void netmem_set_dma_index(netmem_ref netmem,
+ unsigned long id)
+{
+ unsigned long magic;
+
+ if (WARN_ON_ONCE(netmem_is_net_iov(netmem)))
+ return;
+
+ magic = netmem_get_pp_magic(netmem) | (id << PP_DMA_INDEX_SHIFT);
+ __netmem_clear_lsb(netmem)->pp_magic = magic;
+}
#endif
@@ -226,6 +226,8 @@ static int page_pool_init(struct page_pool *pool,
return -EINVAL;
pool->dma_map = true;
+
+ xa_init_flags(&pool->dma_mapped, XA_FLAGS_ALLOC1);
}
if (pool->slow.flags & PP_FLAG_DMA_SYNC_DEV) {
@@ -275,9 +277,6 @@ static int page_pool_init(struct page_pool *pool,
/* Driver calling page_pool_create() also call page_pool_destroy() */
refcount_set(&pool->user_cnt, 1);
- if (pool->dma_map)
- get_device(pool->p.dev);
-
if (pool->slow.flags & PP_FLAG_ALLOW_UNREADABLE_NETMEM) {
/* We rely on rtnl_lock()ing to make sure netdev_rx_queue
* configuration doesn't change while we're initializing
@@ -325,7 +324,7 @@ static void page_pool_uninit(struct page_pool *pool)
ptr_ring_cleanup(&pool->ring, NULL);
if (pool->dma_map)
- put_device(pool->p.dev);
+ xa_destroy(&pool->dma_mapped);
#ifdef CONFIG_PAGE_POOL_STATS
if (!pool->system)
@@ -471,9 +470,11 @@ page_pool_dma_sync_for_device(const struct page_pool *pool,
__page_pool_dma_sync_for_device(pool, netmem, dma_sync_size);
}
-static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem)
+static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem, gfp_t gfp)
{
dma_addr_t dma;
+ int err;
+ u32 id;
/* 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
@@ -487,15 +488,28 @@ static bool page_pool_dma_map(struct page_pool *pool, netmem_ref netmem)
if (dma_mapping_error(pool->p.dev, dma))
return false;
- if (page_pool_set_dma_addr_netmem(netmem, dma))
+ if (in_softirq())
+ err = xa_alloc(&pool->dma_mapped, &id, netmem_to_page(netmem),
+ PP_DMA_INDEX_LIMIT, gfp);
+ else
+ err = xa_alloc_bh(&pool->dma_mapped, &id, netmem_to_page(netmem),
+ PP_DMA_INDEX_LIMIT, gfp);
+ if (err) {
+ WARN_ONCE(1, "couldn't track DMA mapping, please report to netdev@");
goto unmap_failed;
+ }
+ if (page_pool_set_dma_addr_netmem(netmem, dma)) {
+ WARN_ONCE(1, "unexpected DMA address, please report to netdev@");
+ goto unmap_failed;
+ }
+
+ netmem_set_dma_index(netmem, id);
page_pool_dma_sync_for_device(pool, netmem, pool->p.max_len);
return true;
unmap_failed:
- WARN_ONCE(1, "unexpected DMA address, please report to netdev@");
dma_unmap_page_attrs(pool->p.dev, dma,
PAGE_SIZE << pool->p.order, pool->p.dma_dir,
DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
@@ -512,7 +526,7 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
if (unlikely(!page))
return NULL;
- if (pool->dma_map && unlikely(!page_pool_dma_map(pool, page_to_netmem(page)))) {
+ if (pool->dma_map && unlikely(!page_pool_dma_map(pool, page_to_netmem(page), gfp))) {
put_page(page);
return NULL;
}
@@ -558,7 +572,7 @@ static noinline netmem_ref __page_pool_alloc_pages_slow(struct page_pool *pool,
*/
for (i = 0; i < nr_pages; i++) {
netmem = pool->alloc.cache[i];
- if (dma_map && unlikely(!page_pool_dma_map(pool, netmem))) {
+ if (dma_map && unlikely(!page_pool_dma_map(pool, netmem, gfp))) {
put_page(netmem_to_page(netmem));
continue;
}
@@ -660,6 +674,8 @@ void page_pool_clear_pp_info(netmem_ref netmem)
static __always_inline void __page_pool_release_page_dma(struct page_pool *pool,
netmem_ref netmem)
{
+ struct page *old, *page = netmem_to_page(netmem);
+ unsigned long id;
dma_addr_t dma;
if (!pool->dma_map)
@@ -668,6 +684,17 @@ static __always_inline void __page_pool_release_page_dma(struct page_pool *pool,
*/
return;
+ id = netmem_get_dma_index(netmem);
+ if (!id)
+ return;
+
+ if (in_softirq())
+ old = xa_cmpxchg(&pool->dma_mapped, id, page, NULL, 0);
+ else
+ old = xa_cmpxchg_bh(&pool->dma_mapped, id, page, NULL, 0);
+ if (old != page)
+ return;
+
dma = page_pool_get_dma_addr_netmem(netmem);
/* When page is unmapped, it cannot be returned to our pool */
@@ -675,6 +702,7 @@ static __always_inline void __page_pool_release_page_dma(struct page_pool *pool,
PAGE_SIZE << pool->p.order, pool->p.dma_dir,
DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
page_pool_set_dma_addr_netmem(netmem, 0);
+ netmem_set_dma_index(netmem, 0);
}
/* Disconnects a page (from a page_pool). API users can have a need
@@ -1084,8 +1112,32 @@ static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
static void page_pool_scrub(struct page_pool *pool)
{
+ unsigned long id;
+ void *ptr;
+
page_pool_empty_alloc_cache_once(pool);
- pool->destroy_cnt++;
+ if (!pool->destroy_cnt++ && pool->dma_map) {
+ if (pool->dma_sync) {
+ /* paired with READ_ONCE in
+ * page_pool_dma_sync_for_device() and
+ * __page_pool_dma_sync_for_cpu()
+ */
+ WRITE_ONCE(pool->dma_sync, false);
+
+ /* Make sure all concurrent returns that may see the old
+ * value of dma_sync (and thus perform a sync) have
+ * finished before doing the unmapping below. Skip the
+ * wait if the device doesn't actually need syncing, or
+ * if there are no outstanding mapped pages.
+ */
+ if (dma_dev_need_sync(pool->p.dev) &&
+ !xa_empty(&pool->dma_mapped))
+ synchronize_net();
+ }
+
+ xa_for_each(&pool->dma_mapped, id, ptr)
+ __page_pool_release_page_dma(pool, page_to_netmem(ptr));
+ }
/* No more consumers should exist, but producers could still
* be in-flight.
When enabling DMA mapping in page_pool, pages are kept DMA mapped until they are released from the pool, to avoid the overhead of re-mapping the pages every time they are used. This causes resource leaks and/or crashes when there are pages still outstanding while the device is torn down, because page_pool will attempt an unmap through a non-existent DMA device on the subsequent page return. To fix this, implement a simple tracking of outstanding DMA-mapped pages in page pool using an xarray. This was first suggested by Mina[0], and turns out to be fairly straight forward: We simply store pointers to pages directly in the xarray with xa_alloc() when they are first DMA mapped, and remove them from the array on unmap. Then, when a page pool is torn down, it can simply walk the xarray and unmap all pages still present there before returning, which also allows us to get rid of the get/put_device() calls in page_pool. Using xa_cmpxchg(), no additional synchronisation is needed, as a page will only ever be unmapped once. To avoid having to walk the entire xarray on unmap to find the page reference, we stash the ID assigned by xa_alloc() into the page structure itself, using the upper bits of the pp_magic field. This requires a couple of defines to avoid conflicting with the POINTER_POISON_DELTA define, but this is all evaluated at compile-time, so does not affect run-time performance. The bitmap calculations in this patch gives the following number of bits for different architectures: - 24 bits on 32-bit architectures - 21 bits on PPC64 (because of the definition of ILLEGAL_POINTER_VALUE) - 32 bits on other 64-bit architectures Since all the tracking is performed on DMA map/unmap, no additional code is needed in the fast path, meaning the performance overhead of this tracking is negligible. A micro-benchmark shows that the total overhead of using xarray for this purpose is about 400 ns (39 cycles(tsc) 395.218 ns; sum for both map and unmap[1]). Since this cost is only paid on DMA map and unmap, it seems like an acceptable cost to fix the late unmap issue. Further optimisation can narrow the cases where this cost is paid (for instance by eliding the tracking when DMA map/unmap is a no-op). The extra memory needed to track the pages is neatly encapsulated inside xarray, which uses the 'struct xa_node' structure to track items. This structure is 576 bytes long, with slots for 64 items, meaning that a full node occurs only 9 bytes of overhead per slot it tracks (in practice, it probably won't be this efficient, but in any case it should be an acceptable overhead). [0] https://lore.kernel.org/all/CAHS8izPg7B5DwKfSuzz-iOop_YRbk3Sd6Y4rX7KBG9DcVJcyWg@mail.gmail.com/ [1] https://lore.kernel.org/r/ae07144c-9295-4c9d-a400-153bb689fe9e@huawei.com Reported-by: Yonglong Liu <liuyonglong@huawei.com> Closes: https://lore.kernel.org/r/8743264a-9700-4227-a556-5f931c720211@huawei.com Fixes: ff7d6b27f894 ("page_pool: refurbish version of page_pool code") Suggested-by: Mina Almasry <almasrymina@google.com> Reviewed-by: Mina Almasry <almasrymina@google.com> Reviewed-by: Jesper Dangaard Brouer <hawk@kernel.org> Tested-by: Jesper Dangaard Brouer <hawk@kernel.org> Tested-by: Qiuling Ren <qren@redhat.com> Tested-by: Yuying Ma <yuma@redhat.com> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> --- include/net/page_pool/types.h | 36 +++++++++++++++++++--- net/core/netmem_priv.h | 28 ++++++++++++++++- net/core/page_pool.c | 72 +++++++++++++++++++++++++++++++++++++------ 3 files changed, 121 insertions(+), 15 deletions(-)