| Message ID | 20250212092552.1779679-1-linyunsheng@huawei.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | fix the DMA API misuse problem for page_pool | expand |
On Wed, Feb 12, 2025 at 05:25:47PM +0800, Yunsheng Lin wrote: > This patchset fix the dma API misuse problem as mentioned in [1]. > > 1. https://lore.kernel.org/lkml/8067f204-1380-4d37-8ffd-007fc6f26738@kernel.org/T/ That's a very long and complicated thread. I gave up. You need to provide a proper description of the problem.
On 2025/2/13 2:53, Matthew Wilcox wrote: > On Wed, Feb 12, 2025 at 05:25:47PM +0800, Yunsheng Lin wrote: >> This patchset fix the dma API misuse problem as mentioned in [1]. >> >> 1. https://lore.kernel.org/lkml/8067f204-1380-4d37-8ffd-007fc6f26738@kernel.org/T/ > > That's a very long and complicated thread. I gave up. You need to > provide a proper description of the problem. The description of the problem is in the commit log of patch 2 as something below: "Networking driver with page_pool support may hand over page still with dma mapping to network stack and try to reuse that page after network stack is done with it and passes it back to page_pool to avoid the penalty of dma mapping/unmapping. With all the caching in the network stack, some pages may be held in the network stack without returning to the page_pool soon enough, and with VF disable causing the driver unbound, the page_pool does not stop the driver from doing it's unbounding work, instead page_pool uses workqueue to check if there is some pages coming back from the network stack periodically, if there is any, it will do the dma unmmapping related cleanup work. As mentioned in [1], attempting DMA unmaps after the driver has already unbound may leak resources or at worst corrupt memory. Fundamentally, the page pool code cannot allow DMA mappings to outlive the driver they belong to." The description of the fixing is also in the commit log of patch 2 as below: "By using the 'struct page_pool_item' referenced by page->pp_item, page_pool is not only able to keep track of the inflight page to do dma unmmaping if some pages are still handled in networking stack when page_pool_destroy() is called, and networking stack is also able to find the page_pool owning the page when returning pages back into page_pool: 1. When a page is added to the page_pool, an item is deleted from pool->hold_items and set the 'pp_netmem' pointing to that page and set item->state and item->pp_netmem accordingly in order to keep track of that page, refill from pool->release_items when pool->hold_items is empty or use the item from pool->slow_items when fast items run out. 2. When a page is released from the page_pool, it is able to tell which page_pool this page belongs to by masking off the lower bits of the pointer to page_pool_item *item, as the 'struct page_pool_item_block' is stored in the top of a struct page. And after clearing the pp_item->state', the item for the released page is added back to pool->release_items so that it can be reused for new pages or just free it when it is from the pool->slow_items. 3. When page_pool_destroy() is called, item->state is used to tell if a specific item is being used/dma mapped or not by scanning all the item blocks in pool->item_blocks, then item->netmem can be used to do the dma unmmaping if the corresponding inflight page is dma mapped." it is worth to mention that the changing of page->pp to page->pp_item for the above fix may be able to enable the decoupling page_pool from using the metadata of 'struct page' if folios only provide a memdesc pointer to the page_pool subsystem in the future as pp_item may be used as the metadata replacement of existing 'struct page'. >
This patchset fix the dma API misuse problem as mentioned in [1]. From the below performance data, the overhead is not so obvious due to performance variations in arm64 server and less than 1 ns in x86 server for time_bench_page_pool01_fast_path() and time_bench_page_pool02_ptr_ring, and there is about 10~20ns overhead for time_bench_page_pool03_slow(), see more detail in [2]. arm64 server: Before this patchset: fast_path ptr_ring slow 1. 31.171 ns 60.980 ns 164.917 ns 2. 28.824 ns 60.891 ns 170.241 ns 3. 14.236 ns 60.583 ns 164.355 ns With patchset: 6. 26.163 ns 53.781 ns 189.450 ns 7. 26.189 ns 53.798 ns 189.466 ns X86 server: | Test name |Cycles | 1-5 | | Nanosec | 1-5 | | % | | (tasklet_*)|Before | After |diff| Before | After | diff | change | |------------+-------+-------+----+---------+--------+--------+--------| | fast_path | 19 | 19 | 0| 5.399 | 5.492 | 0.093 | 1.7 | | ptr_ring | 54 | 57 | 3| 15.090 | 15.849 | 0.759 | 5.0 | | slow | 238 | 284 | 46| 66.134 | 78.909 | 12.775 | 19.3 | And about 16 bytes of memory is also needed for each page_pool owned page to fix the dma API misuse problem 1. https://lore.kernel.org/lkml/8067f204-1380-4d37-8ffd-007fc6f26738@kernel.org/T/ 2. https://lore.kernel.org/all/f558df7a-d983-4fc5-8358-faf251994d23@kernel.org/ CC: Alexander Lobakin <aleksander.lobakin@intel.com> CC: Robin Murphy <robin.murphy@arm.com> CC: Alexander Duyck <alexander.duyck@gmail.com> CC: Andrew Morton <akpm@linux-foundation.org> CC: IOMMU <iommu@lists.linux.dev> CC: MM <linux-mm@kvack.org> Change log: V9. 1. Drop the fix of a possible time window problem for NPAI recycling. 2. Add design description for the fix in patch 2. V8: 1. Drop last 3 patch as it causes observable performance degradation for x86 system. 2. Remove rcu read lock in page_pool_napi_local(). 3. Renaming item function more consistently. V7: 1. Fix a used-after-free bug reported by KASAN as mentioned by Jakub. 2. Fix the 'netmem' variable not setting up correctly bug as mentioned by Simon. V6: 1. Repost based on latest net-next. 2. Rename page_pool_to_pp() to page_pool_get_pp(). V5: 1. Support unlimit inflight pages. 2. Add some optimization to avoid the overhead of fixing bug. V4: 1. use scanning to do the unmapping 2. spilt dma sync skipping into separate patch V3: 1. Target net-next tree instead of net tree. 2. Narrow the rcu lock as the discussion in v2. 3. Check the ummapping cnt against the inflight cnt. V2: 1. Add a item_full stat. 2. Use container_of() for page_pool_to_pp(). Yunsheng Lin (4): page_pool: introduce page_pool_get_pp() API page_pool: fix IOMMU crash when driver has already unbound page_pool: support unlimited number of inflight pages page_pool: skip dma sync operation for inflight pages drivers/net/ethernet/freescale/fec_main.c | 8 +- .../ethernet/google/gve/gve_buffer_mgmt_dqo.c | 2 +- drivers/net/ethernet/intel/iavf/iavf_txrx.c | 6 +- drivers/net/ethernet/intel/idpf/idpf_txrx.c | 14 +- drivers/net/ethernet/intel/libeth/rx.c | 2 +- .../net/ethernet/mellanox/mlx5/core/en/xdp.c | 3 +- drivers/net/netdevsim/netdev.c | 6 +- drivers/net/wireless/mediatek/mt76/mt76.h | 2 +- include/linux/mm_types.h | 2 +- include/linux/skbuff.h | 1 + include/net/libeth/rx.h | 3 +- include/net/netmem.h | 31 +- include/net/page_pool/helpers.h | 15 + include/net/page_pool/memory_provider.h | 2 +- include/net/page_pool/types.h | 46 +- net/core/devmem.c | 6 +- net/core/netmem_priv.h | 5 +- net/core/page_pool.c | 423 ++++++++++++++++-- net/core/page_pool_priv.h | 10 +- 19 files changed, 504 insertions(+), 83 deletions(-)