From: Toke Høiland-Jørgensen <toke@redhat.com> mainline inclusion from mainline-v6.16-rc1 commit ee62ce7a1d909ccba0399680a03c2dee83bcae95 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/ICPKD5 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... ------------------------------------------ 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: - 23 bits on 32-bit architectures - 21 bits on PPC64 (because of the definition of ILLEGAL_POINTER_VALUE) - 32 bits on other 64-bit architectures Stashing a value into the unused bits of pp_magic does have the effect that it can make the value stored there lie outside the unmappable range (as governed by the mmap_min_addr sysctl), for architectures that don't define ILLEGAL_POINTER_VALUE. This means that if one of the pointers that is aliased to the pp_magic field (such as page->lru.next) is dereferenced while the page is owned by page_pool, that could lead to a dereference into userspace, which is a security concern. The risk of this is mitigated by the fact that (a) we always clear pp_magic before releasing a page from page_pool, and (b) this would need a use-after-free bug for struct page, which can have many other risks since page->lru.next is used as a generic list pointer in multiple places in the kernel. As such, with this patch we take the position that this risk is negligible in practice. For more discussion, see[1]. Since all the tracking added in this patch is performed on DMA map/unmap, no additional code is needed in the fast path, meaning the performance overhead of this tracking is negligible there. A micro-benchmark shows that the total overhead of the tracking itself is about 400 ns (39 cycles(tsc) 395.218 ns; sum for both map and unmap[2]). 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_YRbk3Sd6Y4rX7KBG9DcVJc... [1] https://lore.kernel.org/r/20250320023202.GA25514@openwall.com [2] 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> Tested-by: Yonglong Liu <liuyonglong@huawei.com> Acked-by: Jesper Dangaard Brouer <hawk@kernel.org> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Link: https://patch.msgid.link/20250409-page-pool-track-dma-v9-2-6a9ef2e0cba8@redh... Signed-off-by: Jakub Kicinski <kuba@kernel.org> Conflicts: include/linux/mm.h include/net/page_pool/types.h include/linux/poison.h net/core/netmem_priv.h net/core/page_pool.c [commit 5796d3967c09, 239e9a90c887 and 1a251f52cfdc are not backport lead to conflicts in mm.h. commit 8ab79ed50cf1, 57afb4830157, 4dec64c52e24 (use netmem) and 403f11ac9ab7(add dma_sync) are not backport lead to conflicts in other files] Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> --- include/linux/mm.h | 52 +++++++++++++++++++-- include/linux/poison.h | 4 ++ include/net/page_pool/types.h | 6 +++ net/core/page_pool.c | 86 +++++++++++++++++++++++++++++++---- 4 files changed, 135 insertions(+), 13 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index cdf1c47c872b..346a19e9749d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -4355,13 +4355,57 @@ static inline bool vma_is_peer_shared(struct vm_area_struct *vma) } #endif +/* + * DMA mapping IDs for page_pool + * + * When DMA-mapping a page, page_pool allocates an ID (from an xarray) and + * stashes it in the upper bits of page->pp_magic. We always want to be able to + * unambiguously identify page pool pages (using page_pool_page_is_pp()). Non-PP + * pages can have arbitrary kernel pointers stored in the same field as pp_magic + * (since it overlaps with page->lru.next), so we must ensure that we cannot + * mistake a valid kernel pointer with any of the values we write into this + * field. + * + * On architectures that set POISON_POINTER_DELTA, this is already ensured, + * since this value becomes part of PP_SIGNATURE; meaning we can just use the + * space between the PP_SIGNATURE value (without POISON_POINTER_DELTA), and the + * lowest bits of POISON_POINTER_DELTA. On arches where POISON_POINTER_DELTA is + * 0, we make sure that we leave the two topmost bits empty, as that guarantees + * we won't mistake a valid kernel pointer for a value we set, regardless of the + * VMSPLIT setting. + * + * Altogether, this means that the number of bits available is constrained by + * the size of an unsigned long (at the upper end, subtracting two bits per the + * above), and the definition of PP_SIGNATURE (with or without + * POISON_POINTER_DELTA). + */ +#define PP_DMA_INDEX_SHIFT (1 + __fls(PP_SIGNATURE - POISON_POINTER_DELTA)) + +/* Hardcode the MIN macro in the below commit: + * 1a251f52cfdc ("minmax: make generic MIN() and MAX() macros available everywhere") + */ +#define PP_MIN(x, y) ((x) < (y) ? (x) : (y)) + +#if POISON_POINTER_DELTA > 0 +/* PP_SIGNATURE includes POISON_POINTER_DELTA, so limit the size of the DMA + * index to not overlap with that if set + */ +#define PP_DMA_INDEX_BITS PP_MIN(32, __ffs(POISON_POINTER_DELTA) - PP_DMA_INDEX_SHIFT) +#else +/* Always leave out the topmost two; see above. */ +#define PP_DMA_INDEX_BITS PP_MIN(32, BITS_PER_LONG - PP_DMA_INDEX_SHIFT - 2) +#endif + +#define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \ + PP_DMA_INDEX_SHIFT) + /* 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) #ifdef CONFIG_PAGE_POOL static inline bool page_pool_page_is_pp(struct page *page) diff --git a/include/linux/poison.h b/include/linux/poison.h index 851a855d3868..96f09b600af2 100644 --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -79,6 +79,10 @@ #define KEY_DESTROY 0xbd /********** net/core/page_pool.c **********/ +/* + * page_pool uses additional free bits within this value to store data, see the + * definition of PP_DMA_INDEX_MASK in mm.h + */ #define PP_SIGNATURE (0x40 + POISON_POINTER_DELTA) /********** net/core/skbuff.c **********/ diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h index b5b6d0438c38..8c796de47b21 100644 --- a/include/net/page_pool/types.h +++ b/include/net/page_pool/types.h @@ -6,6 +6,7 @@ #include <linux/dma-direction.h> #include <linux/ptr_ring.h> #include <linux/kabi.h> +#include <linux/xarray.h> #define PP_FLAG_DMA_MAP BIT(0) /* Should page_pool do the DMA * map/unmap @@ -23,6 +24,9 @@ PP_FLAG_DMA_SYNC_DEV |\ PP_FLAG_PAGE_FRAG) +/* Index limit to stay within PP_DMA_INDEX_BITS for DMA indices */ +#define PP_DMA_INDEX_LIMIT XA_LIMIT(1, BIT(PP_DMA_INDEX_BITS) - 1) + /* * Fast allocation side cache array/stack * @@ -168,6 +172,8 @@ struct page_pool { */ struct ptr_ring ring; + 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; diff --git a/net/core/page_pool.c b/net/core/page_pool.c index 7e3404ee40d9..f55aa48f528b 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -233,8 +233,7 @@ 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->p.flags & PP_FLAG_DMA_MAP) - get_device(pool->p.dev); + xa_init_flags(&pool->dma_mapped, XA_FLAGS_ALLOC1); return 0; } @@ -347,9 +346,24 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool, pool->p.dma_dir); } -static bool page_pool_dma_map(struct page_pool *pool, struct page *page) +static unsigned long page_get_dma_index(struct page *page) +{ + return (page->pp_magic & PP_DMA_INDEX_MASK) >> PP_DMA_INDEX_SHIFT; +} + +static void page_set_dma_index(struct page *page, unsigned long id) +{ + unsigned long magic; + + magic = page->pp_magic | (id << PP_DMA_INDEX_SHIFT); + page->pp_magic = magic; +} + +static bool page_pool_dma_map(struct page_pool *pool, struct page *page, 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 @@ -363,7 +377,23 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page) if (dma_mapping_error(pool->p.dev, dma)) return false; + if (in_softirq()) + err = xa_alloc(&pool->dma_mapped, &id, page, PP_DMA_INDEX_LIMIT, + gfp); + else + err = xa_alloc_bh(&pool->dma_mapped, &id, page, + PP_DMA_INDEX_LIMIT, gfp); + + if (err) { + WARN_ONCE(err != -ENOMEM, "couldn't track DMA mapping, 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); + return false; + } + page_pool_set_dma_addr(page, dma); + page_set_dma_index(page, id); if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) page_pool_dma_sync_for_device(pool, page, pool->p.max_len); @@ -397,7 +427,7 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool, return NULL; if ((pool->p.flags & PP_FLAG_DMA_MAP) && - unlikely(!page_pool_dma_map(pool, page))) { + unlikely(!page_pool_dma_map(pool, page, gfp))) { put_page(page); return NULL; } @@ -444,7 +474,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool, for (i = 0; i < nr_pages; i++) { page = pool->alloc.cache[i]; if ((pp_flags & PP_FLAG_DMA_MAP) && - unlikely(!page_pool_dma_map(pool, page))) { + unlikely(!page_pool_dma_map(pool, page, gfp))) { put_page(page); continue; } @@ -509,6 +539,8 @@ static s32 page_pool_inflight(struct page_pool *pool) static __always_inline void __page_pool_release_page_dma(struct page_pool *pool, struct page *page) { + struct page *old; + unsigned long id; dma_addr_t dma; if (!(pool->p.flags & PP_FLAG_DMA_MAP)) @@ -517,6 +549,18 @@ void __page_pool_release_page_dma(struct page_pool *pool, struct page *page) */ return; + id = page_get_dma_index(page); + 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(page); /* When page is unmapped, it cannot be returned to our pool */ @@ -524,6 +568,7 @@ void __page_pool_release_page_dma(struct page_pool *pool, struct page *page) PAGE_SIZE << pool->p.order, pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING); page_pool_set_dma_addr(page, 0); + page_set_dma_index(page, 0); } /* Disconnects a page (from a page_pool). API users can have a need @@ -609,9 +654,13 @@ __page_pool_put_page(struct page_pool *pool, struct page *page, if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page))) { /* Read barrier done in page_ref_count / READ_ONCE */ - if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) + if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) { + /* re-check under rcu_read_lock() to sync with page_pool_scrub() */ + rcu_read_lock(); page_pool_dma_sync_for_device(pool, page, dma_sync_size); + rcu_read_unlock(); + } if (allow_direct && in_softirq() && page_pool_recycle_in_cache(page, pool)) @@ -813,8 +862,7 @@ static void page_pool_free(struct page_pool *pool) ptr_ring_cleanup(&pool->ring, NULL); - if (pool->p.flags & PP_FLAG_DMA_MAP) - put_device(pool->p.dev); + xa_destroy(&pool->dma_mapped); #ifdef CONFIG_PAGE_POOL_STATS free_percpu(pool->recycle_stats); @@ -841,8 +889,28 @@ 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->p.flags & PP_FLAG_DMA_MAP) { + if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) { + /* Disable page_pool_dma_sync_for_device() */ + pool->p.flags &= ~PP_FLAG_DMA_SYNC_DEV; + + /* 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 (!xa_empty(&pool->dma_mapped)) + synchronize_net(); + } + + xa_for_each(&pool->dma_mapped, id, ptr) + __page_pool_release_page_dma(pool, ptr); + } /* No more consumers should exist, but producers could still * be in-flight. -- 2.25.1