linux-kernel - Re: [PATCH v1 2/2] swiotlb: Fix slot alignment checks

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Date:   Wed, 5 Apr 2023 06:40:19 +0200
From:   Petr Tesařík <petr@...arici.cz>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     Dexuan-Linux Cui <dexuan.linux@...il.com>,
        Petr Tesarik <petrtesarik@...weicloud.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jianxiong Gao <jxgao@...gle.com>,
        David Stevens <stevensd@...omium.org>,
        Joerg Roedel <jroedel@...e.de>,
        "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
        open list <linux-kernel@...r.kernel.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] swiotlb: Fix slot alignment checks

Hi Dexuan,

On Tue, 4 Apr 2023 20:11:18 +0000
Dexuan Cui <decui@...rosoft.com> wrote:

> > From: Dexuan-Linux Cui <dexuan.linux@...il.com>
> > Sent: Tuesday, April 4, 2023 12:55 PM
> > 
> > On Tue, Mar 21, 2023 at 1:37 AM Petr Tesarik
> > <petrtesarik@...weicloud.com> wrote:
> > ...
> > 
> > Hi Petr, this patch has gone into the mainline:
> > 0eee5ae10256 ("swiotlb: fix slot alignment checks")
> > 
> > Somehow it breaks Linux VMs on Hyper-V: a regular VM with
> > swiotlb=force or a confidential VM (which uses swiotlb) fails to boot.
> > If I revert this patch, everything works fine.  
> 
> The log is pasted below. Looks like the SCSI driver hv_storvsc fails to
> detect the disk capacity:

The first thing I can imagine is that there are in fact no (free) slots
in the SWIOTLB which match the alignment constraints, so the map
operation fails. However, this would result in a "swiotlb buffer is
full" message in the log, and I can see no such message in the log
excerpt you have posted.

Please, can you check if there are any "swiotlb" messages preceding the
first error message?

Petr T