6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Larysa Zaremba larysa.zaremba@intel.com
[ Upstream commit ac9a48a6f1610b094072b815e884e1668aea4401 ]
When the umem is shared, the DMA mapping is also shared between the xsk pools, therefore it should stay valid as long as at least 1 user remains. However, the pool also keeps the copies of DMA-related information that are initialized in the same way in xp_init_dma_info(), but cleared by xp_dma_unmap() only for the last remaining pool, this causes the problems below.
The first one is that the commit adbf5a42341f ("ice: remove af_xdp_zc_qps bitmap") relies on pool->dev to determine the presence of a ZC pool on a given queue, avoiding internal bookkeeping. This works perfectly fine if the UMEM is not shared, but reliably fails otherwise as stated in the linked report.
The second one is pool->dma_pages which is dynamically allocated and only freed in xp_dma_unmap(), this leads to a small memory leak. kmemleak does not catch it, but by printing the allocation results after terminating the userspace program it is possible to see that all addresses except the one belonging to the last detached pool are still accessible through the kmemleak dump functionality.
Always clear the DMA mapping information from the pool and free pool->dma_pages when unmapping the pool, so that the only difference between results of the last remaining user's call and the ones before would be the destruction of the DMA mapping.
Fixes: adbf5a42341f ("ice: remove af_xdp_zc_qps bitmap") Fixes: 921b68692abb ("xsk: Enable sharing of dma mappings") Reported-by: Alasdair McWilliam alasdair.mcwilliam@outlook.com Closes: https://lore.kernel.org/PA4P194MB10056F208AF221D043F57A3D86512@PA4P194MB1005... Acked-by: Maciej Fijalkowski maciej.fijalkowski@intel.com Signed-off-by: Larysa Zaremba larysa.zaremba@intel.com Link: https://lore.kernel.org/r/20241122112912.89881-1-larysa.zaremba@intel.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/xdp/xsk_buff_pool.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c index b0a611677865d..f38388b6b62c2 100644 --- a/net/xdp/xsk_buff_pool.c +++ b/net/xdp/xsk_buff_pool.c @@ -369,10 +369,9 @@ void xp_dma_unmap(struct xsk_buff_pool *pool, unsigned long attrs) return; }
- if (!refcount_dec_and_test(&dma_map->users)) - return; + if (refcount_dec_and_test(&dma_map->users)) + __xp_dma_unmap(dma_map, attrs);
- __xp_dma_unmap(dma_map, attrs); kvfree(pool->dma_pages); pool->dma_pages = NULL; pool->dma_pages_cnt = 0;