From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EEF246C4BC for ; Tue, 21 Jul 2026 18:59:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784660353; cv=none; b=ctSfIbN1CIoYZZ9msR3RzvHRG7VAxv+YvC+Oo1BIrpIPkUwDGERwclbhKTNFg//hKx16bnl8fozrxF8KH+EwnmqZZYUehbhuji4hb8w3iO/+KEzp5O8NAIo5c/V4RG5YT0mqwpIU+aCAbMIgEKYJIW+souGnkiB8FJtXfw3zsSM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784660353; c=relaxed/simple; bh=EzPj6s+LOwBuzumgfTubt2qQor3yQZI5LBfK5uIBntA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hXXzEQTJ5+tFx4cHeT29UjHGru/pieXnCQ6Peb9Fmq7JFrEV/Dh5Serw6ETFLMbF9O+5rCQ4h9KM655XIKkL0NPUOCx6TkaCGigPZarSd1FG1yXnXOpVTJTzxk7EFLkKTryYUlrMsh9qQX5VcHO/6KYk99m3d5B4ZZbhROySP/E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bmNlCCwn; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bmNlCCwn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC0001F00A3A; Tue, 21 Jul 2026 18:59:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784660349; bh=2TCqFz5uQmSI9a1R6ZrsEia6/ThTF0g48t814vf69fs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bmNlCCwnyfYBCK3zVjSmeowWr9z2vPYFX6Hyq/+cSeR5RmtqkTITY28di2aj7Ts2c rkfCNCK7iHjek19C82DseHmC/h2iiyqAHPyl0OU69xangYCrm60SMifZ50tpB9Q0ig pT4gGaSTAMMUBvdtD9jFeie7vNRR9DRX5KyTCf70KLgjX4dCcfIGvNWhzelqRnNMjn aS1czIg23uMtPsUL2dGYE05ZamdoFwFV1/gS/5voUKYhkfc40+eLUQa+oBLnCvTMQ4 YrLfyLTRQULX2W9qtcbS1UBe9DF81Ygg/oBiG+GPYp7eQ9XHaFlmFu+tXs8nmrTeeb Ay3bymtu/GAiw== From: Sasha Levin To: stable@vger.kernel.org Cc: Mikhail Gavrilov , Vivek Kasireddy , Sasha Levin Subject: [PATCH 5.15.y 2/2] dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning Date: Tue, 21 Jul 2026 14:59:06 -0400 Message-ID: <20260721185906.397615-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260721185906.397615-1-sashal@kernel.org> References: <2026071652-dandelion-handbook-8d52@gregkh> <20260721185906.397615-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Mikhail Gavrilov [ Upstream commit 504e2b4ab97a51d56d966cd36d0997ad30b65b2d ] When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM driver (e.g. amdgpu for video playback in GNOME Videos / Showtime) triggers a spurious warning: DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \ overlapping mappings aren't supported WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0 The call chain is: amdgpu_cs_ioctl -> amdgpu_ttm_backend_bind -> dma_buf_map_attachment -> [udmabuf] map_udmabuf -> get_sg_table -> dma_map_sgtable(dev, sg, direction, 0) // attrs=0 -> debug_dma_map_sg -> add_dma_entry -> EEXIST This happens because udmabuf builds a per-page scatter-gather list via sg_set_folio(). When begin_cpu_udmabuf() has already created an sg table mapped for the misc device, and an importer such as amdgpu maps the same pages for its own device via map_udmabuf(), the DMA debug infrastructure sees two active mappings whose physical addresses share cacheline boundaries and warns about the overlap. The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in add_dma_entry() because it signals that no CPU cache maintenance is performed at map/unmap time, making the cacheline overlap harmless. All other major dma-buf exporters already pass this flag: - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC The CPU sync at map/unmap time is also redundant for udmabuf: begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU access is requested through the dma-buf interface. Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and dma_unmap_sgtable() in udmabuf to suppress the spurious warning and skip the redundant sync. Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access hooks") Cc: stable@vger.kernel.org Signed-off-by: Mikhail Gavrilov Acked-by: Vivek Kasireddy Signed-off-by: Vivek Kasireddy Link: https://patch.msgid.link/20260331061657.79983-1-mikhail.v.gavrilov@gmail.com Signed-off-by: Sasha Levin --- drivers/dma-buf/udmabuf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 3cd9c4a84e76fb..68ffa01ced63db 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -73,7 +73,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, if (ret < 0) goto err_alloc; - ret = dma_map_sgtable(dev, sg, direction, 0); + ret = dma_map_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC); if (ret < 0) goto err_map; return sg; @@ -88,7 +88,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, static void put_sg_table(struct device *dev, struct sg_table *sg, enum dma_data_direction direction) { - dma_unmap_sgtable(dev, sg, direction, 0); + dma_unmap_sgtable(dev, sg, direction, DMA_ATTR_SKIP_CPU_SYNC); sg_free_table(sg); kfree(sg); } -- 2.53.0