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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 10AC4C433DB for ; Thu, 21 Jan 2021 20:10:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D762C23A5C for ; Thu, 21 Jan 2021 20:10:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726282AbhAUUKZ (ORCPT ); Thu, 21 Jan 2021 15:10:25 -0500 Received: from foss.arm.com ([217.140.110.172]:45078 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726847AbhAUUJb (ORCPT ); Thu, 21 Jan 2021 15:09:31 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EF84511D4; Thu, 21 Jan 2021 12:08:45 -0800 (PST) Received: from [10.57.39.58] (unknown [10.57.39.58]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DF64C3F66E; Thu, 21 Jan 2021 12:08:43 -0800 (PST) Subject: Re: [PATCH] ACPI/IORT: Do not blindly trust DMA masks from firmware To: Moritz Fischer , lorenzo.pieralisi@arm.com Cc: guohanjun@huawei.com, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, moritzf@google.com, sudeep.holla@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org References: <20210121191612.90387-1-mdf@kernel.org> From: Robin Murphy Message-ID: Date: Thu, 21 Jan 2021 20:08:42 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210121191612.90387-1-mdf@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-01-21 19:16, Moritz Fischer wrote: > Address issue observed on real world system with suboptimal IORT table > where DMA masks of PCI devices would get set to 0 as result. > > iort_dma_setup() would query the root complex' IORT entry for a DMA > mask, and use that over the one the device has been configured with > earlier. > > Ideally we want to use the minimum mask of what the IORT contains for > the root complex and what the device was configured with, but never 0. > > Fixes: 5ac65e8c8941 ("ACPI/IORT: Support address size limit for root complexes") > Signed-off-by: Moritz Fischer > --- > Hi all, > > not sure I'm doing this right, but I think the current behavior (while a > corner case) seems to also fail for 32 bit devices if the IORT specifies > 64 bit. It works on my test system now with a 32 bit device. I suppose it could go wrong if it's an old driver that doesn't explicitly set its own masks and assumes they will always be 32-bit. Technically we'd consider that the driver's fault these days, but there's a lot of legacy around still. > Open to suggestions for better solutions (and maybe the > nc_dma_get_range() should have the same sanity check?) Honestly the more I come back to this, the more I think we should give up trying to be clever and just leave the default masks alone beyond the initial "is anything set up at all?" sanity checks. Setting the bus limit is what really matters these days, and should be sufficient to encode any genuine restriction. There's certainly no real need to widen the default masks above 32 bits just because firmware suggests so, since the driver should definitely be calling dma_set_mask() and friends later if it's >32-bit capable anyway. > Thanks, > Moritz > > --- > drivers/acpi/arm64/iort.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c > index d4eac6d7e9fb..c48eabf8c121 100644 > --- a/drivers/acpi/arm64/iort.c > +++ b/drivers/acpi/arm64/iort.c > @@ -1126,6 +1126,11 @@ static int rc_dma_get_range(struct device *dev, u64 *size) > > rc = (struct acpi_iort_root_complex *)node->node_data; > > + if (!rc->memory_address_limit) { > + dev_warn(dev, "Root complex has broken memory_address_limit\n"); Probably warrants a FW_BUG in there. > + return -EINVAL; > + } > + > *size = rc->memory_address_limit >= 64 ? U64_MAX : > 1ULL<memory_address_limit; > > @@ -1172,9 +1177,9 @@ void iort_dma_setup(struct device *dev, u64 *dma_addr, u64 *dma_size) > */ > end = dmaaddr + size - 1; > mask = DMA_BIT_MASK(ilog2(end) + 1); > - dev->bus_dma_limit = end; > - dev->coherent_dma_mask = mask; > - *dev->dma_mask = mask; > + dev->bus_dma_limit = min_not_zero(dev->bus_dma_limit, end); This doesn't need to change, since the default bus limit is 0 anyway (and that means "no limit"). > + dev->coherent_dma_mask = min_not_zero(dev->coherent_dma_mask, mask); > + *dev->dma_mask = min_not_zero(*dev->dma_mask, mask); AFAICS the only way an empty mask could get here now is from nc_dma_get_range(), so I'd rather see a consistent warning there than just silently start working around that too. Of course IORT doesn't say these fields are optional (other than the lack of a root complex limit in older table versions), so we're giving bad firmware a pass to never be fixed, ho hum... Thanks, Robin. > } > > *dma_addr = dmaaddr; >