Re: 4.19-rc3: IOMMU PT warnings: WARNING: CPU: 0 PID: 1 at mm/page_alloc.c:4065 __alloc_pages_slowpath+0xb7b/0xcd0

[Robin Murphy]

On 10/09/18 14:23, Christoph Hellwig wrote:
> On Mon, Sep 10, 2018 at 11:16:12AM +0300, Meelis Roos wrote:
> > In 4.19-rc1, I found that to keep Intel integrated graphics working when
> > VT-d is on, I need to have IOMMU passthough on or GPU init would fail
> > with DMAR error and the screen would display static gibberish. So I
> > turned IOMMU PT on by default in kernel config. It worked, also in rc2.
> >
> > Now with rc3, it still works but I get some warning splats in dmesg
> > about IOMMU passthrough:
>
> Any chance you could bisect this down to a specific commit?  For
> a start it might be worth if it is reproducable with:
>
>     git://git.infradead.org/users/hch/dma-mapping.git dma-mapping-4.19-2
>
> which were the only dma-mapping changes post -rc2.

Given the __alloc_pages_slowpath() warning, this looks like it's 
probably stemming from the oversized PASID table issue which a few other 
folks have hit too. I think this patch is the most up-to-date fix:

https://www.mail-archive.com/iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx/msg25639.html

Robin.