Re: Fwd: SWIOTLB on 32-bit PAE.

[Christian Melki <christian.melki-VBSoEI6PWPXQT0dZR+AlfA@public.gmane.org>]

Hi.

I think I rang the bell a bit early. The corruption is in grub legacy (I 
assumed that would be in Linux too, but it wasn't). The on disk format 
of ext4 apparently stores byte ordering somehow? I thought the on disk 
format of ext4 was a specific endian (little). Since only that file is 
unreadable in grub, but readable in Linux.. I am guessing endian issues 
somehow.. which still is strange.

Regards,
Christian

On 10/03/2015 08:00 PM, Konrad Rzeszutek Wilk wrote:
> On Sat, Oct 03, 2015 at 09:36:30AM -0500, Bjorn Helgaas wrote:
>> [+cc Konrad, Joerg, iommu list]
>>
>> On Fri, Oct 02, 2015 at 04:20:16PM +0200, Christian Melki wrote:
>>> I discovered a strange error on my machine. 32-bit PAE 4.2.0 without
>>> IOMMU code (yeah, I know).
>>> When writing to an ext4 filesystem on a USB disk my kernel would hang
>>> and not return control to userspace. It would spew kernel messages to
>>> syslog as fast as it could without giving userspace any time, ie "hang"
>>> as far as a user sees it. The device itself is ok and the filesystem is
>>> clean.
>>> I get messages like this, millions of them.
>>>
>>> Oct  2 14:33:06 voodoochild kernel: [  223.287447] nommu_map_sg:
>>> overflow 25dcac000+1024 of device mask ffffffff
>>> Oct  2 14:33:06 voodoochild kernel: [  223.287448] nommu_map_sg:
>>> overflow 25dcac000+1024 of device mask ffffffff
>>> Oct  2 14:33:06 voodoochild kernel: [  223.287449] nommu_map_sg:
>>> overflow 25dcac000+1024 of device mask ffffffff
>>>
>>> I disovered that SWIOTLB was not on. It is only provided for 64-bit
>>> machines where it is default. On 32-bit SWIOTLB seems disabled
>>> unless you are running with some IOMMU/AGPGART code.
>>>
>>> But what about 32-bit PAE? Would that not qualify for SWIOTLB without IOMMU?
>
> It most certainly would!
>>>
>>> I am a novice in this area. Maybe this is a Kconfig "bug" for us
>>> that like to hang ourselves with CONFIG_* rope? :) I'd like to think
>>> that SWIOTLB should be default for 32-bit PAE too?
>
> Aye. I presume that you had done a small change already for this?
> Would you be willing to post it on lkml and CC me ?
>
> Thank you.
>>>
>>> Best regards,
>>> Christian
>>>
>>>
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