Re: [PATCH v3] VT-d: add iommu=igfx option to workaround graphics issues

From: Wei Liu <wei.liu2@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
	Ting-Wei Lan <lantw44@gmail.com>,
	xen-devel@lists.xen.org, Julien Grall <julien.grall@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Yang Zhang <yang.z.zhang@intel.com>
Subject: Re: [PATCH v3] VT-d: add iommu=igfx option to workaround graphics issues
Date: Wed, 5 Aug 2015 14:35:24 +0100	[thread overview]
Message-ID: <20150805133524.GN26074@zion.uk.xensource.com> (raw)
In-Reply-To: <55C1FEFD.4040205@citrix.com>

On Wed, Aug 05, 2015 at 01:18:05PM +0100, Andrew Cooper wrote:
> On 05/08/15 10:11, 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 option to control whether Intel graphics IOMMU is enabled.
> > Running Xen with iommu=no-igfx is similar to running Linux with
> > intel_iommu=igfx_off, which disables IOMMU for Intel GPU. This can be
> > used by users to manually workaround the problem before a fix is
> > available for i915 driver.
> >
> > Signed-off-by: Ting-Wei Lan <lantw44@gmail.com>
> > Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> Wei: I think this is a candidate for inclusion into 4.6
> 

This patch is straight-forward and it's basically risk free. So

Release-acked-by: Wei Liu <wei.liu2@citrix.com>

(subject to an ack from vt-d maintainers)

> ~Andrew
> 
> > ---
> > Changed since v2:
> >   * Make no-igfx available for all Intel devices, not just Calpella/Ironlake
> > Changed since v1:
> >   * Replace igfx_off with igfx
> >
> >  docs/misc/xen-command-line.markdown  | 11 ++++++++++-
> >  xen/drivers/passthrough/iommu.c      |  3 +++
> >  xen/drivers/passthrough/vtd/quirks.c |  3 +++
> >  xen/include/xen/iommu.h              |  2 +-
> >  4 files changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
> > index 13f03ad..486e53b 100644
> > --- a/docs/misc/xen-command-line.markdown
> > +++ b/docs/misc/xen-command-line.markdown
> > @@ -793,7 +793,7 @@ debug hypervisor only).
> >  > Default: `new` unless directed-EOI is supported
> >  
> >  ### iommu
> > -> `= List of [ <boolean> | force | required | intremap | qinval | snoop | sharept | dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug | verbose | debug ]`
> > +> `= List of [ <boolean> | force | required | intremap | qinval | snoop | sharept | dom0-passthrough | dom0-strict | amd-iommu-perdev-intremap | workaround_bios_bug | igfx | verbose | debug ]`
> >  
> >  > Sub-options:
> >  
> > @@ -867,6 +867,15 @@ debug hypervisor only).
> >  >> ignored (normally IOMMU setup fails if any of the devices listed by a DRHD
> >  >> entry aren't PCI discoverable).
> >  
> > +> `igfx` (VT-d)
> > +
> > +> Default: `true`
> > +
> > +>> Enable IOMMU for Intel graphics devices. The intended usage of this option
> > +>> is `no-igfx`, which is silimar to Linux `intel_iommu=igfx_off` option used
                               ^
                               similar

Wei.