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 51D4742F70B; Thu, 16 Jul 2026 14:33:49 +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=1784212430; cv=none; b=hUKTjCCju4Ffyb6WKsDf9Npc5SdgNGcTiAch3ziWZFCBN0bhYETpWyayobItrifR1pH3WMF37fYBmJ/3Rw4eYbp9pFzSMl/JPDj5Xc7lqMItAILUwDFHF+KRdtdK7m5HsHu1APutcxSP2T30Xccmkq+1kMKaIY14tRRKsVl6T2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784212430; c=relaxed/simple; bh=blfSaxpcnh5Z3fu3Bo0T8AwtROmSMsqTsWJoRZSB/uk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PIz9DGiJtSYcRjHrawdKwBTeB98tJfXxNwM/ZGlzNKzyZYxZZ9nQeCleDKDDTUzMi4JUv9xcShSIpcC3cMo5GcxqyvsoUCpPnwZ5S7+XyNfUGaRW96uqcSkGDlm4sRfrU5ay5ficp7v3akHdOfSJFDgwMMFMpzcYzPvLJMOZy7k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=p0FWHRvm; 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="p0FWHRvm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 634F51F000E9; Thu, 16 Jul 2026 14:33:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784212428; bh=btsu+W2hEttHsVfKeS1dwtPAPQNBp/lUzZxPCKTbch8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=p0FWHRvm6j3qIOSKZZujy11zHj0jCuP8L8cxaN8yatwAuooOmI9l2+vEuVABKyND9 o5SYcWwfbGEmaKFxnENGxHItDoMJBjYdgY9qcyMmmXrKZr2q+8RRilom3NeHeMqRuD B+Z8vypU7VpJKLgiueLPC5nuq5UJhd1UA5h6716g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Mikhail Gavrilov , Vivek Kasireddy Subject: [PATCH 6.12 322/349] dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning Date: Thu, 16 Jul 2026 15:34:16 +0200 Message-ID: <20260716133040.520933282@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133033.287196923@linuxfoundation.org> References: <20260716133033.287196923@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 6.12-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 @@ -127,7 +127,7 @@ 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; @@ -142,7 +142,7 @@ 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); }