linux-kernel - Re: [PATCH 1/2] iommu: Handle race with default domain setup

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Message-ID: <20250214194343.GE3696814@ziepe.ca>
Date: Fri, 14 Feb 2025 15:43:43 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, Russell King <linux@...linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Stuart Yoder <stuyoder@...il.com>,
	Laurentiu Tudor <laurentiu.tudor@....com>,
	Nipun Gupta <nipun.gupta@....com>,
	Nikhil Agarwal <nikhil.agarwal@....com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Charan Teja Kalla <quic_charante@...cinc.com>
Subject: Re: [PATCH 1/2] iommu: Handle race with default domain setup

On Thu, Feb 13, 2025 at 11:48:59PM +0000, Robin Murphy wrote:
> It turns out that deferred default domain creation leaves a subtle
> race window during iommu_device_register() wherein a client driver may
> asynchronously probe in parallel and get as far as performing DMA API
> operations with dma-direct, only to be switched to iommu-dma underfoot
> once the default domain attachment finally happens, with obviously
> disastrous consequences. Even the wonky of_iommu_configure() path is at
> risk, since iommu_fwspec_init() will no longer defer client probe as the
> instance ops are (necessarily) already registered, and the "replay"
> iommu_probe_device() call can see dev->iommu_group already set and so
> think there's nothing to do either.
> 
> Fortunately we already have the right tool in the right place in the
> form of iommu_device_use_default_domain(), which just needs to ensure
> that said default domain is actually ready to *be* used. Deferring the
> client probe shouldn't have too much impact, given that this only
> happens while the IOMMU driver is probing, and thus due to kick the
> deferred probe list again once it finishes.
> 
> Reported-by: Charan Teja Kalla <quic_charante@...cinc.com>
> Fixes: 98ac73f99bc4 ("iommu: Require a default_domain for all iommu drivers")
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/iommu.c | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason