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

From: Robin Murphy
Date: Mon Sep 10 2018 - 09:26:35 EST

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:// 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: