iommu must be enabled for PVH hardware domain

[Ruslan Makhmatkhanov]

Roger Pau Monné wrote on 05/12/15 18:50:
> Hello,
>
> El 12/05/15 a les 17.20, Ruslan Makhmatkhanov ha escrit:
>> Hello,
>>
>> we have machine with VT-d and EPT-capable CPU:
>> Intel(R) Xeon(R) CPU E5504 [1]
>>
>> The system is FreeBSD 11.0-CURRENT r282694 installed from
>> ftp.freebsd.org iso.
>>
>> But dom0 fails to boot at this hardware with "iommu must be enabled for
>> PVH hardware domain" [2]. VT-d support is indeed not detected at kernel
>> level. Here is dmesg with VT-d enabled in BIOS [3] and dmesg with VT-d
>> disabled in BIOS [4]. It's look like there is no difference on both
>> outputs. Here is the proofpic of that the system is VT-d capable and the
>> support is enabled in BIOS [5]. Here is acpidump -t output [6]
>
> My bet right now is be that Xen detects that your IOMMU contains erratas
> and disables it. Can you add "iommu=debug,force" to your xen_cmdline and
> try again?
>
> Also, can you paste the contents of your /boot/loader.conf?
>
> Roger.

You are right:

[VT-D] Disabling IOMMU due to Intel 5500/5520/X58 Chipset errata #47, #53

and after that:

----------------------------------------------
Panic on CPU 0:
Couldn't enable IOMMU and iommu=required/force
----------------------------------------------

Reboot in five seconds.

But what this means practically? Some chipset bugs preventing us to use 
this feature. Can this circumvented somehow? Thanks.

-- 
Regards,
Ruslan

T.O.S. Of Reality