Re: [Xen-devel] Xen-unstable-staging: Xen BUG at iommu_map.c:455

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Wednesday, April 1, 2015, 1:38:34 AM, you wrote:

> On 31/03/2015 22:11, Sander Eikelenboom wrote:
>> Hi all,
>>
>> I just tested xen-unstable staging (changeset: git:0522407-dirty) 
>>
>> with revert of commit 1aeb1156fa43fe2cd2b5003995b20466cd19a622
>> (due to an already reported but not yet resolved issue)
>>
>> and build with qemu xen from 
>> git://xenbits.xen.org/staging/qemu-upstream-unstable.git
>> (to include the pci command register patch from Jan)
>>
>>
>> and now came across this new splat when starting an HVM with PCI passtrhough:

> Wow - you are getting all the fun bugs at the moment!

> Nothing has changed in the AMD IOMMU driver for a while, but the
> BUG_ON() is particularly unhelpful at identifying what went wrong.

> As a first pass triage, can you rerun with

> diff --git a/xen/drivers/passthrough/amd/iommu_map.c
> b/xen/drivers/passthrough/amd/iommu_map.c
> index 495ff5c..f15c324 100644
> --- a/xen/drivers/passthrough/amd/iommu_map.c
> +++ b/xen/drivers/passthrough/amd/iommu_map.c
> @@ -451,8 +451,9 @@ static int iommu_pde_from_gfn(struct domain *d,
> unsigned long pfn,
>      table = hd->arch.root_table;
>      level = hd->arch.paging_mode;

> -    BUG_ON( table == NULL || level < IOMMU_PAGING_MODE_LEVEL_1 ||
-            level >> IOMMU_PAGING_MODE_LEVEL_6 );
> +    BUG_ON(table == NULL);
> +    BUG_ON(level < IOMMU_PAGING_MODE_LEVEL_1);
+    BUG_ON(level >> IOMMU_PAGING_MODE_LEVEL_6);

>      next_table_mfn = page_to_mfn(table);

> which will help identify which of the conditions is failing.

> Can you please also provide the full serial log, including iommu=debug?

> ~Andrew


Hmm this was very weird .. i tried to get back to a previously working config 
(kernel + xen version) but to no avail .. ran memtest .. removed the cmos 
battery .. warm boots .. cold boots .. nothing seemed to help, always this same
crash when starting the HVM guest with pci passthrough. PV guests with pci 
passthrough worked fine though .. 

Now finally it's working again .. by going back to 4.5.0 release .. and doing a 
baremetal linux boot in between. No idea what helped .. but it was a very 
strange day. But i need the box for the foreseeable future. 

Will see late next week if i have time (and the guts) to try again :-)

--
Sander


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