From: Jason Gunthorpe <jgg@ziepe.ca>
To: Tudor Ambarus <tudor.ambarus@linaro.org>
Cc: Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Lorenzo Pieralisi <lpieralisi@kernel.org>,
"Rob Herring (Arm)" <robh@kernel.org>,
Joerg Roedel <jroedel@suse.de>,
Bjorn Helgaas <bhelgaas@google.com>,
iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
peter.griffin@linaro.org, andre.draszik@linaro.org,
willmcvicker@google.com, jyescas@google.com,
kernel-team@android.com, stable@vger.kernel.org
Subject: Re: [PATCH] iommu: Fix bypass of IOMMU readiness check for multi-IOMMU devices
Date: Mon, 23 Mar 2026 10:54:14 -0300 [thread overview]
Message-ID: <20260323135414.GA8437@ziepe.ca> (raw)
In-Reply-To: <20260323-iommu-ready-check-v1-1-5f6fef8f9f59@linaro.org>
On Mon, Mar 23, 2026 at 01:09:27PM +0000, Tudor Ambarus wrote:
> Commit da33e87bd2bf ("iommu: Handle yet another race around
> registration") introduced a readiness check in `iommu_fwspec_init()` to
> prevent client drivers from configuring their IOMMUs before
> `bus_iommu_probe()` has completed.
>
> To optimize the replay path, the readiness check was conditionally
> gated behind `!dev->iommu`:
> if (!dev->iommu && !READ_ONCE(iommu->ready))
> return -EPROBE_DEFER;
>
> However, this assumption breaks down for devices that map to multiple
> IOMMU instances.
?? We don't directly support "multiple IOMMU instances". There is only
one dev->iommu.
AFAIK if some drivers need to support multiple different instances of
the same IOMMU driver they must deal with this fully internally and
present to the core a "single instance" view.
So, your explanation doesn't make sense to me. If dev->iommu is set
then the driver must be ready, including any multi-instances it has.
If it is not ready then this is really an iommu driver bug, not a core
bug?
Jason
next prev parent reply other threads:[~2026-03-23 13:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-23 13:09 [PATCH] iommu: Fix bypass of IOMMU readiness check for multi-IOMMU devices Tudor Ambarus
2026-03-23 13:54 ` Jason Gunthorpe [this message]
2026-03-23 16:46 ` Tudor Ambarus
2026-03-23 17:31 ` Jason Gunthorpe
2026-03-24 11:40 ` Robin Murphy
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