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 C46023876DE; Thu, 16 Jul 2026 13:56:14 +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=1784210175; cv=none; b=QfB2UAgWuOVF4eg6oqb+AXts/lGFAPuw66uLD2cIC4h6vjF9f6KBjfXGeEU+aA6fE7z/wYXlvdB+oVUQBTxgBmDyVqBsAdGFURV/3QGZld1FQf4QnFxI0olEjXibK3FwFl3TFUy+U9Ji8KcyOAon+dRnRlJ5kxcnYmYkF2yJiYE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784210175; c=relaxed/simple; bh=fnqD7OV6u4ykMerQiNsRnZjI4Zg6srVOsvMqMNFAlIs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jlzSl15So9gPl7hIdx+oe6TALFK6wRxvfUsfgoJrBrQh0yTaY2Bck3JfskopaMTgi8cXmuyfe3B0ZnZPjM//cGZREJ+S9zGlZR/yWsfrAoGW9CPQniAolFZESBBy5A9ZRzFUtrqI8I7wVLvgqjTCvGD3W5ZuIrkjP7DaKl910WY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RR5yQte1; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="RR5yQte1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 351251F00A3A; Thu, 16 Jul 2026 13:56:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784210174; bh=YLsYgJhz8V24M0aaJ3j+oaberEqzUeC6XoC6UjW20SU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RR5yQte1oeVQNDZoR0cLTU9TZoPBXQ0dmC9nHR8YUVGidbnb0VvWiU3bzmGgiVjNF eS56UdJQGg7vSybfw0M9VvESe2izHdwmU/Kqw3A+B+pNLOCs1pF4EmBMBK7qZbrD2t 3ui8fZjG/Ukpv+VBDSd/IadRHYklnzok/S341XEY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Mikhail Gavrilov , Vivek Kasireddy Subject: [PATCH 7.1 466/518] dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning Date: Thu, 16 Jul 2026 15:32:14 +0200 Message-ID: <20260716133058.041462048@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133047.772246337@linuxfoundation.org> References: <20260716133047.772246337@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mikhail Gavrilov commit 504e2b4ab97a51d56d966cd36d0997ad30b65b2d upstream. 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: Greg Kroah-Hartman --- drivers/dma-buf/udmabuf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -163,7 +163,7 @@ static struct sg_table *get_sg_table(str sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE, ubuf->offsets[i]); - 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; @@ -178,7 +178,7 @@ err_alloc: 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); }