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Tue, 31 Mar 2026 00:50:12 -0700 (PDT) Received: from rock-3b.tailb81abf.ts.net ([213.152.28.84]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4887c91f0casm9873015e9.35.2026.03.31.00.50.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2026 00:50:11 -0700 (PDT) From: Midgy BALON To: iommu@lists.linux.dev Cc: joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, heiko@sntech.de, jonas@kwiboo.se, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Midgy BALON Subject: [PATCH] iommu/rockchip: fix page table allocation flags for v2 IOMMU Date: Tue, 31 Mar 2026 09:50:10 +0200 Message-Id: <20260331075010.1463-1-midgy971@gmail.com> X-Mailer: git-send-email 2.30.2 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit commit 2a7e6400f72b ("iommu: rockchip: Allocate tables from all available memory for IOMMU v2") removed GFP_DMA32 from iommu_data_ops_v2, reasoning that RK356x and RK3588 IOMMU v2 hardware supports up to 40-bit physical addresses for page tables. However, the RK3568 IOMMU page-table walker uses a 32-bit AXI bus: it cannot access physical addresses above 4 GB regardless of the address encoding range. On boards with more than 4 GB of RAM (e.g. 8 GB LPDDR4X), removing GFP_DMA32 causes two distinct failure modes: 1. Direct allocation above 4 GB: iommu_alloc_pages_sz() may return memory above 0x100000000. The hardware page-table walker issues a bus error trying to dereference those addresses, causing an IOMMU fault on the first DMA transaction. 2. SWIOTLB bounce-buffer poisoning: without GFP_DMA32, page tables land above the SWIOTLB window. dma_map_single() with DMA_BIT_MASK(32) then bounces them into a buffer below 4 GB. rk_dte_get_page_table() returns phys_to_virt() of the bounce buffer address; PTEs are written there; the next dma_sync_single_for_device(DMA_TO_DEVICE) copies the original (zero) data back over the bounce buffer, silently erasing the freshly written PTEs. The IOMMU faults because every PTE reads as zero. Restore GFP_DMA32 (and DMA_BIT_MASK(32)) for iommu_data_ops_v2, which currently only serves "rockchip,rk3568-iommu" in mainline. Tested on Radxa ROCK 3B (RK3568, 8 GB LPDDR4X): - MobileNetV1 via RKNN: 5.8 ms/inference (IOMMU mode) - YOLOv5s 640x640 via RKNN: ~57 ms/inference (IOMMU mode) - No IOMMU faults, correct inference results Fixes: 2a7e6400f72b ("iommu: rockchip: Allocate tables from all available memory for IOMMU v2") Cc: stable@vger.kernel.org Cc: Jonas Karlman Signed-off-by: Midgy BALON --- drivers/iommu/rockchip-iommu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c index 85f3667e797..8b45db29471 100644 --- a/drivers/iommu/rockchip-iommu.c +++ b/drivers/iommu/rockchip-iommu.c @@ -1358,8 +1358,8 @@ static struct rk_iommu_ops iommu_data_ops_v2 = { .pt_address = &rk_dte_pt_address_v2, .mk_dtentries = &rk_mk_dte_v2, .mk_ptentries = &rk_mk_pte_v2, - .dma_bit_mask = DMA_BIT_MASK(40), - .gfp_flags = 0, + .dma_bit_mask = DMA_BIT_MASK(32), + .gfp_flags = GFP_DMA32, }; static const struct of_device_id rk_iommu_dt_ids[] = { -- 2.30.2