Re: Fwd: SWIOTLB on 32-bit PAE

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Oct 05, 2015 at 12:44:55PM +0200, Christian Melki wrote:
> Joerg,
> 
> I already sent the patch for Kconfig change to the list.
> But I discovered something even more disturbing which I mailed Konrad about.
> With the change my machine does not hang any more, but instead corrupts data
> which is written. The data however is readable on the machine which
> corrupted it, unreadable on the other machine without the patch. I don't
> understand what is going on. I have never encountered "selective" file
> corruption of fs on different machines. The fs itself checks out cleanly
> with badblock control (ext4). I fail to understand what is happening.

And I believe this ended up being an operator error?

With the patch you sent, you didn't include your SoB 
(Signed-off-By). I would like to include your patch but I cannot
with your SoB. It is matter of reading to Documentation/SubmittingPatches
and just consenting to the Certificate in there.

If you are uncomfortable with that - that is OK, I can make this
patch myself (a one liner :-)) but I figured it owuld be nice
for you to have all the credit.
> 
> Regards,
> Christian
> 
> -------- Forwarded Message --------
> Subject: SWIOTLB on 32-bit PAE
> Date: Mon, 5 Oct 2015 10:31:39 +0200
> From: Christian Melki <christian.melki@t2data.com>
> To: linux-kernel@vger.kernel.org
> CC: konrad.wilk@oracle.com
> 
> Hi,
> 
> I discovered that my 32-bit PAE 4.2.0 kernel (no IOMMU code) would hang
> when writing to my USB disk. The kernel spews million(-ish messages per
> sec) to syslog, effectively "hanging" userspace with my kernel.
> 
> 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
> ... etc ...
> 
> In my kernel config I noticed that SWIOTLB was not on. It seems SWIOTLB
> is provided for 64-bit and 32-bit with IOMMU/AGPGART code. But if I
> compiled the kernel with PAE and no IOMMU and no other GART code, I
> would not get SWIOTLB. I'd like to think that SWIOTLB should be selected
> for 32-bit PAE as default.
> 
> I have attached a oneliner patch which does that.
> The patch works for me. The issue where the kernel more or less runs
> endless bashing of (nommu_?)map_sg when failing is another problem I
> guess. I expected the kernel/drivers to have some more graceful
> handling, but I know to little about this area to have a proper opinion.
> 
> Regards,
> Christian
> 
> 
> 

> diff -urN linux-4.2.orig/arch/x86/Kconfig linux-4.2/arch/x86/Kconfig
> --- linux-4.2.orig/arch/x86/Kconfig	2015-10-05 08:56:58.933313678 +0200
> +++ linux-4.2/arch/x86/Kconfig	2015-10-05 09:00:00.916306025 +0200
> @@ -1282,6 +1282,7 @@
>  config X86_PAE
>  	bool "PAE (Physical Address Extension) Support"
>  	depends on X86_32 && !HIGHMEM4G
> +	select SWIOTLB
>  	---help---
>  	  PAE is required for NX support, and furthermore enables
>  	  larger swapspace support for non-overcommit purposes. It
>