linux-kernel - Re: [PATCH v4 5/5] iommu/dma: Force swiotlb_max_mapping

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Message-ID: <Zd4CcL3Nnvybw2xF@infradead.org>
Date: Tue, 27 Feb 2024 07:40:32 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	iommu@...ts.linux.dev, Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Petr Tesarik <petr.tesarik1@...wei-partners.com>,
	Dexuan Cui <decui@...rosoft.com>,
	Nicolin Chen <nicolinc@...dia.com>,
	Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v4 5/5] iommu/dma: Force swiotlb_max_mapping_size on an
 untrusted device

On Wed, Feb 21, 2024 at 11:35:04AM +0000, Will Deacon wrote:
> +static size_t iommu_dma_max_mapping_size(struct device *dev)
> +{
> +	if (is_swiotlb_active(dev) && dev_is_untrusted(dev))
> +		return swiotlb_max_mapping_size(dev);

Curious: do we really need both checks here?  If swiotlb is active
for a device (for whatever reason), aren't we then always bound
by the max size?  If not please add a comment explaining it.