linux-kernel - Re: 4.19-rc3: IOMMU PT warnings: WARNING: CPU: 0 PID: 1 at mm/page_alloc.c:4065 __alloc_pages

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Date:   Mon, 10 Sep 2018 14:26:30 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, Meelis Roos <mroos@...ux.ee>
Cc:     iommu@...ts.linux-foundation.org,
        Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: 4.19-rc3: IOMMU PT warnings: WARNING: CPU: 0 PID: 1 at
 mm/page_alloc.c:4065 __alloc_pages_slowpath+0xb7b/0xcd0

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@lists.linux-foundation.org/msg25639.html

Robin.