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Date:   Thu, 23 Nov 2023 11:16:08 +0100
From:   Petr =?UTF-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Halil Pasic <pasic@linux.ibm.com>,
        Niklas Schnelle <schnelle@linux.ibm.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Petr Tesarik <petr.tesarik1@huawei-partners.com>,
        Ross Lagerwall <ross.lagerwall@citrix.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Jianxiong Gao <jxgao@google.com>
Subject: Re: Memory corruption with CONFIG_SWIOTLB_DYNAMIC=y
Message-ID: <20231123111608.17727968@meshulam.tesarici.cz>
In-Reply-To: <20231108101347.77cab795@meshulam.tesarici.cz>
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        <20231103214831.26d29f4d@meshulam.tesarici.cz>
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        <20231108101347.77cab795@meshulam.tesarici.cz>
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Hello everybody,

I don't think I have ever seen an answer to my question regarding
alignment constraints on swiotlb bounce buffers:

On Wed, 8 Nov 2023 10:13:47 +0100
Petr Tesa=C5=99=C3=ADk <petr@tesarici.cz> wrote:

>[...]
> To sum it up, there are two types of alignment:
>=20
> 1. specified by a device's min_align_mask; this says how many low
>    bits of a buffer's physical address must be preserved,
>=20
> 2. specified by allocation size and/or the alignment parameter;
>    this says how many low bits in the first IO TLB slot's physical
>    address must be zero.
>=20
> I hope somebody can confirm or correct this summary before I go
> and break something. You know, it's not like cleanups in SWIOTLB
> have never broken anything.  ;-)

If no answer means that nobody knows, then based on my understanding the
existing code (both implementation and users), I can assume that this
is the correct interpretation.

I'm giving it a few more days. If there's still no reaction, expect a
beautiful documentation patch and a less beautiful cleanup patch in the
next week.

Petr T