Re: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Juergen Gross <jgross@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Roman Shaposhnik <roman@zededa.com>,
	Paul Durrant <Paul.Durrant@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>
Subject: Re: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx
Date: Wed, 7 Aug 2019 12:17:20 +0200	[thread overview]
Message-ID: <20190807101720.cgzaqv23yhexwzov@Air-de-Roger> (raw)
In-Reply-To: <8a68c4c0-4f50-4e04-786c-7426fdc10db9@suse.com>

On Wed, Aug 07, 2019 at 10:31:40AM +0200, Jan Beulich wrote:
> On 07.08.2019 09:35, Roger Pau Monné  wrote:
> > On Tue, Aug 06, 2019 at 02:48:51PM -0700, Roman Shaposhnik wrote:
> > > On Tue, Aug 6, 2019 at 9:18 AM Roger Pau Monné <roger.pau@citrix.com> wrote:
> > > > 
> > > > On Fri, Aug 02, 2019 at 10:05:40AM +0200, Roger Pau Monné wrote:
> > > > > On Thu, Aug 01, 2019 at 11:25:04AM -0700, Roman Shaposhnik wrote:
> > > > > > This patch completely fixes the problem for me!
> > > > > > 
> > > > > > Thanks Roger! I'd love to see this in Xen 4.13
> > > > > 
> > > > > Thanks for testing!
> > > > > 
> > > > > It's still not clear to me why the previous approach didn't work, but
> > > > > I think this patch is better because it removes the usage of
> > > > > {set/clear}_identity_p2m_entry from PV domains. I will submit this
> > > > > formally now.
> > > > 
> > > > Sorry to bother again, but since we still don't understand why the
> > > > previous fix didn't work for you, and I can't reproduce this with my
> > > > hardware, could you give the attached patch a try?
> > > 
> > > No worries -- and thanks for helping to get it over the finish line --
> > > this is much appreciated!
> > > 
> > > I'm happy to say that this latest patch is also working just fine. So
> > > I guess this is the one that's going to land in Xen 4.13?
> > 
> > No, not really, sorry this was still a debug patch.
> > 
> > So I think the behaviour you are seeing can only be explained if the
> > IOMMU is already enabled by the firmware when booting into Xen, can
> > this be the case?
> 
> Even then - why would the existing flush not suffice in this case?

It should indeed, I'm just trying to figure out what's different in
his setup.

Also I'm not sure the iommu init code was designed taking into account
that the iommu DMA translation might already be enabled by the
firmware.

Roger.

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