linux-kernel - Re: [PATCH v3 03/33] iommu/io-pgtable-arm: Add quirk to quiet WARN

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Message-ID: <20250429122834.GA2260621@ziepe.ca>
Date: Tue, 29 Apr 2025 09:28:34 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org, Connor Abbott <cwabbott0@...il.com>,
	Rob Clark <robdclark@...omium.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Nicolin Chen <nicolinc@...dia.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Joao Martins <joao.m.martins@...cle.com>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU SUBSYSTEM" <iommu@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 03/33] iommu/io-pgtable-arm: Add quirk to quiet
 WARN_ON()

On Mon, Apr 28, 2025 at 01:54:10PM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> In situations where mapping/unmapping squence 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.

I think if you want to do something like that using the iommu API the
expectation is for the caller to do a iova_to_phys to check what is
mapped first? That seems kind of lame..

Maybe page table driver should not not be doing these WARNs at all. If
we want to check for that the core iommu code should have the WARN_ON?

eg iommufd already has a WARN_ON around iommu_unmap failures so having
one in the ARM page table is a double WARN.

Don't really like using a quirk to change the API contract.

Jason