linux-kernel - Re: [PATCH 2/2] swiotlb: Enforce page alignment in swiotlb

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Message-ID: <20240129075043.GA22019@lst.de>
Date: Mon, 29 Jan 2024 08:50:43 +0100
From: Christoph Hellwig <hch@....de>
To: Petr Tesařík <petr@...arici.cz>
Cc: Christoph Hellwig <hch@....de>, Will Deacon <will@...nel.org>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	iommu@...ts.linux.dev, Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Petr Tesarik <petr.tesarik1@...wei-partners.com>,
	Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH 2/2] swiotlb: Enforce page alignment in swiotlb_alloc()

On Mon, Jan 29, 2024 at 08:43:26AM +0100, Petr Tesařík wrote:
> > So PFN_DOWN aligns the address and thus per se converting the unaligned
> > address isn't a problem.  That being said swiotlb obviously should never
> > allocate unaligned addresses, but the placement of this check feels
> > odd to me.  Also because it only catches swiotlb_alloc and not the
> > map side.
> 
> We may have to rethink how alignment constraints are interpreted. See
> also my reply to PATCH 1/2.
> 
> > Maybe just throw a WARN_ON_ONCE into slot_addr() ?
> 
> Yes.
> 
> Or, what if I write a KUnit test suite for swiotlb to combat this
> constant stream of various regressions?

Both sounds good to me.