Re: [Xen-devel] Xen 4.0.0-rc7 problem/hang with vt-d DMAR parsing

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Mar 24, 2010 at 09:52:45AM +0800, Cui, Dexuan wrote:
> Pasi K?rkk?inen wrote:
> > On Tue, Mar 23, 2010 at 07:54:33PM +0000, Keir Fraser wrote:
> >> On 23/03/2010 19:37, "Pasi Kärkkäinen" <pasik@xxxxxx> wrote:
> >> 
> >>>> It's not impossible that the BIOS VT-d support is just broken (I
> >>>> assume you've never tested VT-d on this particular type of system
> >>>> before). 
> >>> 
> >>> Yeah, I've never used VT-d on this system earlier, so it could just
> >>> be broken BIOS. I guess Xen still shouldn't hang on it?
> >> 
> >> We'd prefer to gracefully disable VT-d.
> >> 
> > 
> > 4.0.0-rc7 (without any extra cmdline options) does disable vt-d and
> > boot ok, after 'hanging' for 30 seconds while parsing the DMAR tables.
> > 
> > If I add "iommu=verbose" option for Xen, then it'll print huge amount
> > of stuff like I pasted earlier.. and it takes forever to print all
> > that. 
> > 
> > Hmm.. wondering if the patch Jan just sent will help with that.
> > Sounds like it might help :)
> I guess Jan's patch helps here in a very interesting way:
> I suspect your BIOS doesn't construct the DMAR properly, e.g., in 
> acpi_parse_dmar(),  entry_header->length is always 0, so xen'll hang in the 
> while loop and continue printing the "dmaru->address = 0" message when 
> iommu=verbose.
> Without verbose message outputing, the loop runs even faster and in 
> acpi_parse_one_drhd(),  xmalloc(struct acpi_drhd_unit) would NULL in a short 
> periof of time and hence VT-d is got disabled... :-)
> 
> Please dump your DMAR table using the 'acpudump' utility in *native Linux*:
> # wget 
> http://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools-20100123.tar.gz
> # tar zxf pmtools-20100123.tar.gz
> # cd pmtools-20100123/acpidump && make && ./acpidump --table DMAR -b > 
> dmar.bin
> Please attach the dmar.bin so we can double check.
> 

Thanks, I'll provide the dmar table later when I have access to the machine 
again.

-- Pasi


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