linux-kernel - Re: Memory corruption with CONFIG_SWIOTLB

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Message-ID: <20231123111608.17727968@meshulam.tesarici.cz>
Date:   Thu, 23 Nov 2023 11:16:08 +0100
From:   Petr Tesařík <petr@...arici.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     Halil Pasic <pasic@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Petr Tesarik <petr.tesarik1@...wei-partners.com>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Jianxiong Gao <jxgao@...gle.com>
Subject: Re: Memory corruption with CONFIG_SWIOTLB_DYNAMIC=y

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 Tesařík <petr@...arici.cz> wrote:

>[...]
> To sum it up, there are two types of alignment:
> 
> 1. specified by a device's min_align_mask; this says how many low
>    bits of a buffer's physical address must be preserved,
> 
> 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.
> 
> 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