linux-kernel - Re: 5.13 i915/PAT regression on Brasswell, adding nopat to the kernel commandline worksaround this

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Message-ID: <3b178f66-fde6-888a-9a49-ab0d13e944b3@redhat.com>
Date:   Wed, 12 May 2021 14:36:30 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Christoph Hellwig <hch@....de>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     intel-gfx@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        x86@...nel.org
Subject: Re: 5.13 i915/PAT regression on Brasswell, adding nopat to the kernel
 commandline worksaround this

Hi,

On 5/12/21 1:57 PM, Christoph Hellwig wrote:
> On Wed, May 12, 2021 at 01:15:03PM +0200, Peter Zijlstra wrote:
>> IIRC it's because of 74ffa5a3e685 ("mm: add remap_pfn_range_notrack"),
>> which added a sanity check to make sure expectations were met. It turns
>> out they were not.
>>
>> The bug is not new, the warning is. AFAIK the i915 team is aware, but
>> other than that I've not followed.
> 
> 
> The actual culprit is b12d691ea5e0 ("i915: fix remap_io_sg to verify the
> pgprot"), but otherwise agreed.  Someone the i915 maintainers all seem
> to be on vacation as the previous report did not manage to trigger any
> kind of reply.

I can confirm that reverting that commit restores i915 functionality with
5.13-rc1 on the Braswell machine on which I have been testing this.

Regards,

Hans