linux-kernel - Re: [PATCH v2] iommu/io-pgtable-arm: Add quirk to quiet WARN

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Message-ID: <20250507155717.GD33739@ziepe.ca>
Date: Wed, 7 May 2025 12:57:17 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Rob Clark <robdclark@...il.com>, iommu@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
	Rob Clark <robdclark@...omium.org>, Will Deacon <will@...nel.org>,
	Joerg Roedel <joro@...tes.org>, Kevin Tian <kevin.tian@...el.com>,
	Nicolin Chen <nicolinc@...dia.com>,
	Joao Martins <joao.m.martins@...cle.com>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()

On Wed, May 07, 2025 at 04:09:47PM +0100, Robin Murphy wrote:
> On 07/05/2025 3:40 pm, Jason Gunthorpe wrote:
> > On Wed, May 07, 2025 at 07:29:51AM -0700, Rob Clark wrote:
> > > From: Rob Clark <robdclark@...omium.org>
> > > 
> > > 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 <robdclark@...omium.org>
> > > ---
> > > Sending v2 stand-alone, since I'm not quite ready to send a new
> > > iteration of the full VM_BIND series.  And with selftest_running
> > > removed, I think this patch stands on it's own.  (And maybe there
> > > is still time to sneak this in for v6.16, removing an iommu dep
> > > for the VM_BIND series in v6.17?)
> > 
> > You should just remove the warn on completely, no other driver does this.
> 
> What do you mean "no other driver"?

The server drivers.
 
> From a quick look, these IOMMU drivers have some sort of visible warning
> related to the state of an existing PTE during map/unmap:

Many of them are just using this code.

> while these IOMMU drivers do not:
> 
> amd
> intel
> mtk_iommu_v1
> omap-iommu
> riscv
> sprd-iommu
> tegra-smmu
> virtio-iommu

Which I think proves we don't need it and shouldn't have it.

Jason