Re: Unable to boot Xen 4.8 with iommu=0

[Venu Busireddy <venu.busireddy@oracle.com>]

On Fri, Feb 17, 2017 at 02:29:32PM -0500, Konrad Rzeszutek Wilk wrote:
> On Fri, Feb 17, 2017 at 12:27:25PM -0700, Tamas K Lengyel wrote:
> > On Fri, Feb 17, 2017 at 11:56 AM, Konrad Rzeszutek Wilk
> > <konrad.wilk@oracle.com> wrote:
> > > . snip..
> > >> >> > Given this commit is pretty old, I'm also curious why it's only reported
> > >> >> > on 4.8. Tamas, did you succeed with iommu=0 pre 4.8, or 4.8 happens
> > >> >> > to be the one upon which you first tried iommu=0 on a platform supporting
> > >> >> > interrupt remapping?
> > >> >>
> > >> >> It just happens to be the one I tried. VT-d was spamming my console
> > >> >> with faults like this:
> > >> >>
> > >> >> (XEN) [VT-D]DMAR:[DMA Write] Request device [0000:00:02.0] fault addr
> > >> >> 277e28000, iommu reg = ffff82c000201000
> > ffff82c000201000
> > >> >> (XEN) [VT-D]DMAR: reason 05 - PTE Write access is not set
> > >> >>
> > >> >> So I figured I can just turn it off to clean up my console. I still
> > >> >> don't know what these VT-d faults are about..
> > >> >
> > >> > What is the 0:02.0 device? Is it being passed in to your guest?
> > >>
> > >> Nope, there is no pass-through to any guests. The device is:
> > >>
> > >> 00:02.0 Display controller: Intel Corporation 2nd Generation Core
> > >> Processor Family Integrated Graphics Controller (rev 09)
> > >
> > > Let me guess, you have an SandyBridge motherboard and were using
> > > Intel AMT?
> > 
> > Correct.
> > 
> > >
> > > I see those all the time on that box (and I think my Haswell
> > > one too). The best I could narrow it down was that the card decided that
> > > certain area should be in the RMRR regions. With Venu/Elen's patch
> > > in (see 431685e8deb660976d8e986c41a647944e410c6c) you should be able
> > > to provide an rmrr paramater to include these addresses.
> > 
> > Some more information on how to use that flag would be valuable.. I
> > tried "rmrr=270000000-280000000=00:02.0" to no avail and I really have
> > no idea what I'm doing here =)
> 
> CC-ing Elena and Venu who I hope can help you with this.
> 
> You may want to provide the full 'xl dmesg' as the 'rmrr' should have
> outputted some details..

Tamas,

While 'xl dmesg' and the output from the serial console will certainly
help, it appears that you may have already provided the info needed. There
may be other devices than 0:02.0 that have problems, but let us assume
that it is the only device.

Your change to xen command line is incorrect. The correct option to add
to the xen command line is:

rmrr=0x277e28=0:00:02.0

For the RMRR specification to work, apart from changing the Xen command
line appropriately, you will also need the corresponding patch applied to
your Xen image. The patch has been pushed upstream, but is only available
in 4.9. Did you backport that change and rebuilt your Xen image with
it? Unless you do that, the Xen command line changes won't work.

Good luck!

Venu


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