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,URIBL_BLOCKED, 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 ACFD9C433E0 for ; Tue, 26 Jan 2021 11:50:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 819BD2311C for ; Tue, 26 Jan 2021 11:50:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405330AbhAZLti (ORCPT ); Tue, 26 Jan 2021 06:49:38 -0500 Received: from foss.arm.com ([217.140.110.172]:35260 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392424AbhAZLlt (ORCPT ); Tue, 26 Jan 2021 06:41:49 -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 6BE5F101E; Tue, 26 Jan 2021 03:41:00 -0800 (PST) Received: from [10.57.43.46] (unknown [10.57.43.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 231C13F66B; Tue, 26 Jan 2021 03:40:59 -0800 (PST) Subject: Re: [PATCH v2 1/3] iommu/arm-smmu: Add support for driver IOMMU fault handlers To: Will Deacon , linux-arm-msm@vger.kernel.org, iommu@lists.linux-foundation.org, Greg Kroah-Hartman , Joerg Roedel , Krishna Reddy , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20201124191600.2051751-1-jcrouse@codeaurora.org> <20201124191600.2051751-2-jcrouse@codeaurora.org> <20210122124125.GA24102@willie-the-truck> <8ba2f53d-abbf-af7f-07f6-48ad7f383a37@arm.com> <20210125215107.GB16374@jcrouse1-lnx.qualcomm.com> From: Robin Murphy Message-ID: Date: Tue, 26 Jan 2021 11:40:57 +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: <20210125215107.GB16374@jcrouse1-lnx.qualcomm.com> 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-arm-msm@vger.kernel.org On 2021-01-25 21:51, Jordan Crouse wrote: > On Fri, Jan 22, 2021 at 12:53:17PM +0000, Robin Murphy wrote: >> On 2021-01-22 12:41, Will Deacon wrote: >>> On Tue, Nov 24, 2020 at 12:15:58PM -0700, Jordan Crouse wrote: >>>> Call report_iommu_fault() to allow upper-level drivers to register their >>>> own fault handlers. >>>> >>>> Signed-off-by: Jordan Crouse >>>> --- >>>> >>>> drivers/iommu/arm/arm-smmu/arm-smmu.c | 16 +++++++++++++--- >>>> 1 file changed, 13 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c >>>> index 0f28a8614da3..7fd18bbda8f5 100644 >>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c >>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c >>>> @@ -427,6 +427,7 @@ static irqreturn_t arm_smmu_context_fault(int irq, void *dev) >>>> struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain); >>>> struct arm_smmu_device *smmu = smmu_domain->smmu; >>>> int idx = smmu_domain->cfg.cbndx; >>>> + int ret; >>>> fsr = arm_smmu_cb_read(smmu, idx, ARM_SMMU_CB_FSR); >>>> if (!(fsr & ARM_SMMU_FSR_FAULT)) >>>> @@ -436,11 +437,20 @@ static irqreturn_t arm_smmu_context_fault(int irq, void *dev) >>>> iova = arm_smmu_cb_readq(smmu, idx, ARM_SMMU_CB_FAR); >>>> cbfrsynra = arm_smmu_gr1_read(smmu, ARM_SMMU_GR1_CBFRSYNRA(idx)); >>>> - dev_err_ratelimited(smmu->dev, >>>> - "Unhandled context fault: fsr=0x%x, iova=0x%08lx, fsynr=0x%x, cbfrsynra=0x%x, cb=%d\n", >>>> + ret = report_iommu_fault(domain, dev, iova, >>>> + fsynr & ARM_SMMU_FSYNR0_WNR ? IOMMU_FAULT_WRITE : IOMMU_FAULT_READ); >>>> + >>>> + if (ret == -ENOSYS) >>>> + dev_err_ratelimited(smmu->dev, >>>> + "Unhandled context fault: fsr=0x%x, iova=0x%08lx, fsynr=0x%x, cbfrsynra=0x%x, cb=%d\n", >>>> fsr, iova, fsynr, cbfrsynra, idx); >>>> - arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_FSR, fsr); >>>> + /* >>>> + * If the iommu fault returns an error (except -ENOSYS) then assume that >>>> + * they will handle resuming on their own >>>> + */ >>>> + if (!ret || ret == -ENOSYS) >>>> + arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_FSR, fsr); >>> >>> Hmm, I don't grok this part. If the fault handler returned an error and >>> we don't clear the FSR, won't we just re-take the irq immediately? >> >> If we don't touch the FSR at all, yes. Even if we clear the fault indicator >> bits, the interrupt *might* remain asserted until a stalled transaction is >> actually resolved - that's that lovely IMP-DEF corner. >> >> Robin. >> > > This is for stall-on-fault. The idea is that if the developer chooses to do so > we would stall the GPU after a fault long enough to take a picture of it with > devcoredump and then release the FSR. Since we can't take the devcoredump from > the interrupt handler we schedule it in a worker and then return an error > to let the main handler know that we'll come back around clear the FSR later > when we are done. Sure, but clearing FSR is not writing to RESUME to resolve the stalled transaction(s). You can already snarf the FSR contents from your report_iommu_fault() handler if you want to, so either way I don't see what's gained by not clearing it as expected at the point where we've handled the *interrupt*, even if it will take longer to decide what to do with the underlying *fault* that it signalled. I'm particularly not keen on having unusual behaviour in the core interrupt handling which callers may unwittingly trigger, for the sake of one very-very-driver-specific flow having a slightly richer debugging experience. For actually *handling* faults, I thought we were going to need to hook up the new IOPF fault queue stuff anyway? Robin. > It is assumed that we'll have to turn off interrupts in our handler to allow > this to work. Its all very implementation specific, but then again we're > assuming that if you want to do this then you know what you are doing. > > In that spirit the error that skips the FSR should probably be something > specific instead of "all errors" - that way a well meaning handler that returns > a -EINVAL doesn't accidentally break itself. > > Jordan > >>> I think >>> it would be better to do this unconditionally, and print the "Unhandled >>> context fault" message for any non-zero value of ret. > >>> >>> Will >>> >