From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 710D7CD5BBD for ; Thu, 13 Nov 2025 10:27:02 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CB7E810E123; Thu, 13 Nov 2025 10:27:00 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="a0FKEHiA"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) by gabe.freedesktop.org (Postfix) with ESMTPS id DBC5B10E179; Thu, 13 Nov 2025 10:26:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1763029619; x=1794565619; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=wgBi8c+U/98U2wSjzClD/VctfdhGL//tIxEiATrxW2Y=; b=a0FKEHiA0KHW1/aDHbFL/bEa0rwaDV7VE6FJZKDwOCd5w9JvHAVGzo/M jNGylFPGORzN2u7tqzVhDLvhH5NZthOK40abNTFJ0s2U8Hyq+slAlEOns 2CAQDJDfy99Y6LjkG6hsNEvnwB0u5OHl/jdK32lzLYtbTrmcGblQ66ZsC PBrivDXXjeOr5Wi5P3SfxKBiSm9LkXiDCB5UcDjUPQmysjv9ywbfLdQcG fVWbkzJe+QqEnD6Z2pF1SeNo5zLY6CpyUxlAoM5oHJ+xbl3LLqh5oHMg2 S/I3kOqLXAc8sqKEVNPYHaWH4SjU6DcXRr1QyR8oJMlLrQR9E7l8fxIK+ w==; X-CSE-ConnectionGUID: Dzjxh3JOQ5ukwFUu8yglwA== X-CSE-MsgGUID: k9yGSjsPTK2MCSH7qHXCJA== X-IronPort-AV: E=McAfee;i="6800,10657,11611"; a="68955990" X-IronPort-AV: E=Sophos;i="6.19,301,1754982000"; d="scan'208";a="68955990" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Nov 2025 02:26:59 -0800 X-CSE-ConnectionGUID: BPfAXXCzQkCUWHhGR9FgXw== X-CSE-MsgGUID: znLSp8QkRTCur4ez9wGpIg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,301,1754982000"; d="scan'208";a="189900667" Received: from aotchere-mobl1.ger.corp.intel.com (HELO localhost) ([10.245.246.135]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Nov 2025 02:26:55 -0800 From: Jani Nikula To: "Kandpal, Suraj" , "dri-devel@lists.freedesktop.org" , "intel-xe@lists.freedesktop.org" , "intel-gfx@lists.freedesktop.org" Cc: "Nautiyal, Ankit K" , "Murthy, Arun R" , "Deak, Imre" Subject: RE: [PATCH] drm/display/dp_mst: Add protection against 0 vcpi In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20251113043918.716367-1-suraj.kandpal@intel.com> Date: Thu, 13 Nov 2025 12:26:53 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" On Thu, 13 Nov 2025, "Kandpal, Suraj" wrote: > .deak@intel.com>; Kandpal, >> Suraj >> Subject: Re: [PATCH] drm/display/dp_mst: Add protection against 0 vcpi >> >> On Thu, 13 Nov 2025, Suraj Kandpal wrote: >> > When releasing a timeslot there is a slight chance we may end up with >> > the wrong payload mask due to overflow if the delayed_destroy_work >> > ends up coming into play after a DP 2.1 monitor gets disconnected >> > which causes vcpi to become 0 then we try to make the payload = >> > ~BIT(vcpi - 1) which is a negative shift. >> >> Is that a real scenario or a hypothetical one? >> > > This is a real scenario which ends up throwing the below error > <7> [515.287237] xe 0000:03:00.0: [drm:drm_dp_mst_get_port_malloc [drm_display_helper]] port ffff888126ce9000 (3) > <4> [515.287267] -----------[ cut here ]----------- > <3> [515.287268] UBSAN: shift-out-of-bounds in ../drivers/gpu/drm/display/drm_dp_mst_topology.c:4575:36 > <3> [515.287271] shift exponent -1 is negative > <4> [515.287275] CPU: 7 UID: 0 PID: 3108 Comm: kworker/u64:33 Tainted: G S U 6.17.0-rc6-lgci-xe-xe-3795-3e79699fa1b216e92+ #1 PREEMPT(voluntary) > <4> [515.287279] Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER > <4> [515.287279] Hardware name: ASUS System Product Name/PRIME Z790-P WIFI, BIOS 1645 03/15/2024 > <4> [515.287281] Workqueue: drm_dp_mst_wq drm_dp_delayed_destroy_work [drm_display_helper] > <4> [515.287303] Call Trace: > <4> [515.287304] > <4> [515.287306] dump_stack_lvl+0xc1/0xf0 > <4> [515.287313] dump_stack+0x10/0x20 > <4> [515.287316] __ubsan_handle_shift_out_of_bounds+0x133/0x2e0 > <4> [515.287324] ? drm_atomic_get_private_obj_state+0x186/0x1d0 > <4> [515.287333] drm_dp_atomic_release_time_slots.cold+0x17/0x3d [drm_display_helper] > <4> [515.287355] mst_connector_atomic_check+0x159/0x180 [xe] > <4> [515.287546] drm_atomic_helper_check_modeset+0x4d9/0xfa0 > <4> [515.287550] ? __ww_mutex_lock.constprop.0+0x6f/0x1a60 > <4> [515.287562] intel_atomic_check+0x119/0x2b80 [xe] > <4> [515.287740] ? find_held_lock+0x31/0x90 > <4> [515.287747] ? lock_release+0xce/0x2a0 > <4> [515.287754] drm_atomic_check_only+0x6a2/0xb40 > <4> [515.287758] ? drm_atomic_add_affected_connectors+0x12b/0x140 > <4> [515.287765] drm_atomic_commit+0x6e/0xf0 > <4> [515.287766] ? _pfx__drm_printfn_info+0x10/0x10 > <4> [515.287774] drm_client_modeset_commit_atomic+0x25c/0x2b0 > <4> [515.287794] drm_client_modeset_commit_locked+0x60/0x1b0 > <4> [515.287795] ? mutex_lock_nested+0x1b/0x30 > <4> [515.287801] drm_client_modeset_commit+0x26/0x50 > <4> [515.287804] __drm_fb_helper_restore_fbdev_mode_unlocked+0xdc/0x110 > <4> [515.287810] drm_fb_helper_hotplug_event+0x120/0x140 > <4> [515.287814] drm_fbdev_client_hotplug+0x28/0xd0 > <4> [515.287819] drm_client_hotplug+0x6c/0xf0 > <4> [515.287824] drm_client_dev_hotplug+0x9e/0xd0 > <4> [515.287829] drm_kms_helper_hotplug_event+0x1a/0x30 > <4> [515.287834] drm_dp_delayed_destroy_work+0x3df/0x410 [drm_display_helper] > <4> [515.287861] process_one_work+0x22b/0x6f0 > <4> [515.287874] worker_thread+0x1e8/0x3d0 > <4> [515.287879] ? __pfx_worker_thread+0x10/0x10 > <4> [515.287882] kthread+0x11c/0x250 > <4> [515.287886] ? __pfx_kthread+0x10/0x10 > <4> [515.287890] ret_from_fork+0x2d7/0x310 > <4> [515.287894] ? __pfx_kthread+0x10/0x10 > <4> [515.287897] ret_from_fork_asm+0x1a/0x30 > > Refer to gitlab xe issue: 6303 Both the backtrace and the gitlab reference should be part of the commit message... > > Regards, > Suraj Kandpal > >> > >> > Signed-off-by: Suraj Kandpal >> > --- >> > drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++- >> > 1 file changed, 3 insertions(+), 1 deletion(-) >> > >> > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c >> > b/drivers/gpu/drm/display/drm_dp_mst_topology.c >> > index 64e5c176d5cc..3cf1eafcfcb5 100644 >> > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c >> > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c >> > @@ -4531,6 +4531,7 @@ int drm_dp_atomic_release_time_slots(struct >> drm_atomic_state *state, >> > struct drm_dp_mst_atomic_payload *payload; >> > struct drm_connector_state *old_conn_state, *new_conn_state; >> > bool update_payload = true; >> > + int bit; >> > >> > old_conn_state = drm_atomic_get_old_connector_state(state, port- >> >connector); >> > if (!old_conn_state->crtc) >> > @@ -4572,7 +4573,8 @@ int drm_dp_atomic_release_time_slots(struct >> drm_atomic_state *state, >> > if (!payload->delete) { >> > payload->pbn = 0; >> > payload->delete = true; >> > - topology_state->payload_mask &= ~BIT(payload->vcpi - 1); >> > + bit = payload->vcpi ? payload->vcpi - 1 : 0; >> > + topology_state->payload_mask &= ~BIT(bit); >> > } >> > >> > return 0; >> >> -- >> Jani Nikula, Intel -- Jani Nikula, Intel