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 X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1412C4320A for ; Fri, 20 Aug 2021 21:31:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A83B8610FF for ; Fri, 20 Aug 2021 21:31:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240823AbhHTVcT (ORCPT ); Fri, 20 Aug 2021 17:32:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48222 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231761AbhHTVcP (ORCPT ); Fri, 20 Aug 2021 17:32:15 -0400 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e3e3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A802C061575 for ; Fri, 20 Aug 2021 14:31:37 -0700 (PDT) Received: from localhost.localdomain (unknown [IPv6:2600:8800:8c06:1000::c8f3]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: alyssa) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id C7CEF1F44A8F; Fri, 20 Aug 2021 22:31:33 +0100 (BST) From: Alyssa Rosenzweig To: dri-devel@lists.freedesktop.org Cc: Rob Herring , Tomeu Vizoso , Steven Price , Alyssa Rosenzweig , David Airlie , Daniel Vetter , linux-kernel@vger.kernel.org Subject: [PATCH 0/3] drm/panfrost: Bug fixes for lock_region Date: Fri, 20 Aug 2021 17:31:14 -0400 Message-Id: <20210820213117.13050-1-alyssa.rosenzweig@collabora.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Chris Morgan reported UBSAN errors in panfrost and tracked them down to the size computation in lock_region. This calculation is overcomplicated (seemingly cargo culted from kbase) and can be simplified with kernel helpers and some mathematical identities. The first patch in the series rewrites the calculation in a form avoiding undefined behaviour; Chris confirms it placates UBSAN. While researching this function, I noticed a pair of other potential bugs: Bifrost can lock more than 4GiB at a time, but must lock at least 32KiB at a time. The latter patches in the series handle these cases. The size computation was unit-tested in userspace. Relevant code below, just missing some copypaste definitions for fls64/clamp/etc: #define MIN_LOCK (1ULL << 12) #define MAX_LOCK (1ULL << 48) struct { uint64_t size; uint8_t encoded; } tests[] = { /* Clamping */ { 0, 11 }, { 1, 11 }, { 2, 11 }, { 4095, 11 }, /* Power of two */ { 4096, 11 }, /* Round up */ { 4097, 12 }, { 8192, 12 }, { 16384, 13 }, { 16385, 14 }, /* Maximum */ { ~0ULL, 47 }, }; static uint8_t region_width(uint64_t size) { size = clamp(size, MIN_LOCK, MAX_LOCK); return fls64(size - 1) - 1; } int main(int argc, char **argv) { for (unsigned i = 0; i < ARRAY_SIZE(tests); ++i) { uint64_t test = tests[i].size; uint8_t expected = tests[i].encoded; uint8_t actual = region_width(test); assert(expected == actual); } } Alyssa Rosenzweig (3): drm/panfrost: Simplify lock_region calculation drm/panfrost: Use u64 for size in lock_region drm/panfrost: Clamp lock region to Bifrost minimum drivers/gpu/drm/panfrost/panfrost_mmu.c | 31 +++++++++--------------- drivers/gpu/drm/panfrost/panfrost_regs.h | 2 ++ 2 files changed, 13 insertions(+), 20 deletions(-) -- 2.30.2