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

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Message-ID: <8965ec0a-97d4-423b-97b9-7848454045d0@arm.com>
Date: Wed, 7 May 2025 16:09:47 +0100
From: Robin Murphy <robin.murphy@....com>
To: Jason Gunthorpe <jgg@...pe.ca>, Rob Clark <robdclark@...il.com>
Cc: 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 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"?

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

apple-dart
arm-smmu
arm-smmu-v3
arm-smmu-qcom
exynos-iommu
ipmmu_vmsa
msm_iommu
mtk_iommu
rockchip-iommu
s390-iommu
sun50i-iommu
qcom_iommu

while these IOMMU drivers do not:

amd
intel
mtk_iommu_v1
omap-iommu
riscv
sprd-iommu
tegra-smmu
virtio-iommu

By driver count, warning is literally the majority behaviour :/

Thanks,
Robin.