Re: [PATCH] VT-d: improve RMRR validity checking

[Weidong Han <weidong.han@intel.com>]

Noboru Iwamatsu wrote:
> Hi Weidong,
>
>   
>> I implemented a patch for it. Noboru, pls have a try on your machine.
>> If you use default iommu=1, VT-d will be disabled with warning messages.
>> If you use iommu=workaround_bios_bug, it should enable VT-d and works
>> for you.
>> If you use iommu=force, it panics.
>>     
>
> On my machine, each options have worked as described.
>   

Thanks Noboru.
> I tried:
> xen-unstable c/s 20844 + drhd-ignore.patch + workaround-bios.patch
>   
drhd-ignore.patch was already checked in as c/s 20846. Keir, pls check 
in the workaround-bios.patch. Thanks.

Regards,
Weidong
> Thanks,
> Noboru.
>
>   
>> patch title: VT-d: add "iommu=workaround_bios_bug" option
>> patch description:
>> Add this option to workaround BIOS bugs. Currently it ignores DRHD if
>> "all" devices under its scope are not pci discoverable. This workarounds
>> a BIOS bug in some platforms to make VT-d work. But note that this
>> option doesn't guarantee security, because it might ignore DRHD.
>> So there are 3 options which handle BIOS bugs differently:
>> iommu=1 (default): If detect non-existent device under a DRHD's scope,
>> or find incorrect RMRR setting (base_address > end_address), disable
>> VT-d completely in Xen with warning messages. This guarantees security
>> when VT-d enabled, or just disable VT-d to let Xen work without VT-d.
>> iommu=force: it enforces to enable VT-d in Xen. If VT-d cannot be
>> enabled, it will crashes Xen. This is mainly for users who must need VT-d.
>> iommu=workaround_bogus_bios: it workarounds some BIOS bugs to make VT-d
>> still work. This might be insecure because there might be a device not
>> protected by any DRHD if the device is re-enabled by malicious s/w. This
>> is for users who want to use VT-d regardless of security.
>>
>> Signed-off-by: Weidong Han <weidong.han@intel.com>
>>
>> Regards,
>> Weidong
>>
>> Noboru Iwamatsu wrote:
>>     
>>> Weidong, Keir,
>>>
>>> I agree your suggestions.
>>>
>>> Noboru.
>>>
>>>       
>>>> Keir Fraser wrote:
>>>>         
>>>>> On 25/01/2010 10:45, "Sander Eikelenboom" <linux@eikelenboom.it> wrote:
>>>>>
>>>>>           
>>>>>> a) Could be discussed if panic should be default instead of disabling
>>>>>> iommu or
>>>>>> not, although there seem to be a lot of broken bioses, so that would
>>>>>> lead to a
>>>>>> lot of machines not booting.
>>>>>>             
>>>>> Absolutely not acceptable. Warn and completely disable IOMMU is the
>>>>> correct
>>>>> default causing least pain to the most end users.
>>>>>
>>>>> -- Keir
>>>>>
>>>>>           
>>>> Agree. It should not crash Xen by default due to BIOS issues.
>>>> warn-and-disable is better. It won't impact common Xen users, and if a
>>>> user really wants to use VT-d, he can try iommu=workaround_bogus_bios,
>>>> or directly report to OEM vendor to get it fixed in BIOS. As VT-d is
>>>> used more and more widely, I think the BIOS issues will be found and
>>>> fixed more quickly than before, thus the situation should be better.
>>>>
>>>> Regards,
>>>> Weidong
>>>>
>>>>
>>>>
>>>>         
>>>       
>
>
>