From: Robin Murphy <robin.murphy@arm.com>
To: Aleksandr Fedorov <sanekf@nxt.ru>, Joerg Roedel <joro@8bytes.org>,
Will Deacon <will@kernel.org>,
iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu: explicitly check for NULL in iommu_dma_get_resv_regions()
Date: Thu, 10 Feb 2022 10:43:17 +0000 [thread overview]
Message-ID: <b090141f-0822-609f-429d-ea790d7fc828@arm.com> (raw)
In-Reply-To: <5481021644415780@myt5-a5512e99e394.qloud-c.yandex.net>
On 2022-02-09 14:09, Aleksandr Fedorov wrote:
> iommu_dma_get_resv_regions() assumes that iommu_fwspec field for
> corresponding device is set which is not always true. Since
> iommu_dma_get_resv_regions() seems to be a future-proof generic API
> that can be used by any iommu driver, add an explicit check for NULL.
Except it's not a "generic" interface for drivers to call at random,
it's a helper for retrieving common firmware-based information
specifically for drivers already using the fwspec mechanism for common
firmware bindings. If any driver calls this with a device *without* a
valid fwnode, it deserves to crash because it's done something
fundamentally wrong.
I concur that it's not exactly obvious that "non-IOMMU-specific" means
"based on common firmware bindings, thus implying fwspec".
Robin.
> Currently it can work by accident since compiler can eliminate
> the 'iommu_fwspec' check altogether when CONFIG_ACPI_IORT=n, but
> code elimination from optimizations is not reliable.
>
> Signed-off-by: Aleksandr Fedorov <halcien@gmail.com>
> ---
> A compilation failure has been observed on a gcc-compatible compiler based on EDG.
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index d85d54f2b549..474b1b7211d7 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -382,10 +382,10 @@ void iommu_put_dma_cookie(struct iommu_domain *domain)
> */
> void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list)
> {
> + struct iommu_fwspec *iommu_fwspec = dev_iommu_fwspec_get(dev);
>
> - if (!is_of_node(dev_iommu_fwspec_get(dev)->iommu_fwnode))
> + if (iommu_fwspec && !is_of_node(iommu_fwspec->iommu_fwnode))
> iort_iommu_msi_get_resv_regions(dev, list);
> -
> }
> EXPORT_SYMBOL(iommu_dma_get_resv_regions);
>
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
_______________________________________________
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next prev parent reply other threads:[~2022-02-10 10:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-09 14:09 [PATCH] iommu: explicitly check for NULL in iommu_dma_get_resv_regions() Aleksandr Fedorov
2022-02-10 10:43 ` Robin Murphy [this message]
2022-02-11 10:18 ` Aleksandr Fedorov
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