From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] VT-d: add iommu=igfx_off option to
 workaround graphics issues
Date: Fri, 17 Jul 2015 20:36:22 +0100
Message-ID: <55A95936.608@citrix.com>
References: <1437159952-4134-1-git-send-email-lantw44@gmail.com>
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To: Ting-Wei Lan <lantw44@gmail.com>, xen-devel@lists.xen.org
Cc: Yang Zhang <yang.z.zhang@intel.com>, Kevin Tian <kevin.tian@intel.com>, Jan Beulich <jbeulich@suse.com>
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On 17/07/15 20:05, Ting-Wei Lan wrote:
> When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake
> devices, It is possible to encounter graphics issues that make screen
> unreadable or crash the system. It was reported in freedesktop bugzilla:
>
> https://bugs.freedesktop.org/show_bug.cgi?id=90037
>
> As we still cannot find a proper fix for this problem, this patch adds
> iommu=igfx_off option that is similar to Linux intel_iommu=igfx_off for
> users to manually workaround the problem.
>
> Signed-off-by: Ting-Wei Lan <lantw44@gmail.com>

If the identified Linux change is correct, then the problems is almost
certainly the i915 driver not using appropriate cache flushing
operations on memory of weakened caching type.

Are there any details available on if/how/what snoop features the IGD
and its IOMMU have?

~Andrew