git-latest: kernel oops in IOMMU setup

[Dirk Hohndel <hohndel@infradead.org>]

latest git from Linus. On a Thinkpad x200s with VT-d enabled (if I
disable VT-d, this of course goes away). 

The oops happens very early during boot in device_to_iommu (called
from domain_context_mapping_one).

Looking at the code dump and the disassembled function here's where
the error happens:

static struct intel_iommu *device_to_iommu(u8 bus, u8 devfn)
{
        struct dmar_drhd_unit *drhd = NULL;
        int i;

        for_each_drhd_unit(drhd) {
                if (drhd->ignored)
                        continue;

                for (i = 0; i < drhd->devices_cnt; i++)
                        if (drhd->devices[i]->bus->number == bus &&
--> drhd->devices[0] is NULL
                            drhd->devices[i]->devfn == devfn)
                                return drhd->iommu;


Given how early this happens it's a little hard to provide logs, etc. I
literally used delay_boot=100 and wrote things down by hand (forgot my
digital camera) and then added printk's to verify).

please let me know what other data I should collect.

The system ran fine with the 2.6.28 release kernel.

/D

-- 
Dirk Hohndel
Intel Open Source Technology Center