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 CA805C3ABDD for ; Tue, 20 May 2025 13:06:20 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 47BC310E527; Tue, 20 May 2025 13:06:20 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id BA8DE10E4F7; Tue, 20 May 2025 13:06:18 +0000 (UTC) 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 BD1FB1516; Tue, 20 May 2025 06:06:04 -0700 (PDT) Received: from [10.57.79.215] (unknown [10.57.79.215]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C0CB13F5A1; Tue, 20 May 2025 06:06:15 -0700 (PDT) Message-ID: Date: Tue, 20 May 2025 14:06:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 05/40] iommu/io-pgtable-arm: Add quirk to quiet WARN_ON() To: Will Deacon , Rob Clark Cc: dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, Connor Abbott , Rob Clark , Joerg Roedel , Jason Gunthorpe , Nicolin Chen , Kevin Tian , Joao Martins , "moderated list:ARM SMMU DRIVERS" , "open list:IOMMU SUBSYSTEM" , open list References: <20250514175527.42488-1-robdclark@gmail.com> <20250514175527.42488-6-robdclark@gmail.com> <20250515143309.GA12165@willie-the-truck> <20250520113146.GA18435@willie-the-truck> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20250520113146.GA18435@willie-the-truck> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 2025-05-20 12:31 pm, Will Deacon wrote: > On Thu, May 15, 2025 at 07:48:39AM -0700, Rob Clark wrote: >> On Thu, May 15, 2025 at 7:33 AM Will Deacon wrote: >>> >>> On Wed, May 14, 2025 at 10:53:19AM -0700, Rob Clark wrote: >>>> From: Rob Clark >>>> >>>> In situations where mapping/unmapping sequence can be controlled by >>>> userspace, attempting to map over a region that has not yet been >>>> unmapped is an error. But not something that should spam dmesg. >>>> >>>> Now that there is a quirk, we can also drop the selftest_running >>>> flag, and use the quirk instead for selftests. >>>> >>>> Signed-off-by: Rob Clark >>>> Acked-by: Robin Murphy >>>> Signed-off-by: Rob Clark >>>> --- >>>> drivers/iommu/io-pgtable-arm.c | 27 ++++++++++++++------------- >>>> include/linux/io-pgtable.h | 8 ++++++++ >>>> 2 files changed, 22 insertions(+), 13 deletions(-) >>> >>> [...] >>> >>>> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h >>>> index bba2a51c87d2..639b8f4fb87d 100644 >>>> --- a/include/linux/io-pgtable.h >>>> +++ b/include/linux/io-pgtable.h >>>> @@ -88,6 +88,13 @@ struct io_pgtable_cfg { >>>> * >>>> * IO_PGTABLE_QUIRK_ARM_HD: Enables dirty tracking in stage 1 pagetable. >>>> * IO_PGTABLE_QUIRK_ARM_S2FWB: Use the FWB format for the MemAttrs bits >>>> + * >>>> + * IO_PGTABLE_QUIRK_NO_WARN_ON: Do not WARN_ON() on conflicting >>>> + * mappings, but silently return -EEXISTS. Normally an attempt >>>> + * to map over an existing mapping would indicate some sort of >>>> + * kernel bug, which would justify the WARN_ON(). But for GPU >>>> + * drivers, this could be under control of userspace. Which >>>> + * deserves an error return, but not to spam dmesg. >>>> */ >>>> #define IO_PGTABLE_QUIRK_ARM_NS BIT(0) >>>> #define IO_PGTABLE_QUIRK_NO_PERMS BIT(1) >>>> @@ -97,6 +104,7 @@ struct io_pgtable_cfg { >>>> #define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA BIT(6) >>>> #define IO_PGTABLE_QUIRK_ARM_HD BIT(7) >>>> #define IO_PGTABLE_QUIRK_ARM_S2FWB BIT(8) >>>> + #define IO_PGTABLE_QUIRK_NO_WARN_ON BIT(9) >>> >>> This feels a bit fragile to me: >>> * IOMMU-API users of io-pgtable shouldn't be passing this quirk >>> but might end up doing so to paper over driver bugs. >>> >>> * Low-level users of io-pgtable who expose page-table operations to >>> userspace need to pass the quirk, but might well not bother because >>> well-behaved userspace doesn't trigger the warning. >>> >>> So overall, it's all a bit unsatisfactory. Is there a way we could have >>> the warnings only when invoked via the IOMMU API? >> >> iommu drivers _not_ setting this flag seems like a good way to achieve that ;-) >> >> The alternative is to move the warns to the iommu driver... but they >> could just as easily remove the WARN_ON()s as they could set the >> NO_WARN_ON quirk, so :shrug:? > > Bah, I also don't have a good idea to improve this, so I guess I'll take > what you have for now. Hmm, just a nit on reflection, how about fixing up the name to just IO_PGTABLE_QUIRK_NO_WARN? Given that it's already quite long, and we have a well-established DMA_ATTR_NO_WARN with equivalent semantics over in the DMA API. Cheers, Robin.