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

To: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
From: Andrew Lyon <andrew.lyon@xxxxxxxxx>
Date: Thu, 21 Jan 2010 15:28:42 +0000
Cc: Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, Weidong Han <weidong.han@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "keir.fraser@xxxxxxxxxxxxx" <keir.fraser@xxxxxxxxxxxxx>
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On Thu, Jan 21, 2010 at 2:17 PM, Sander Eikelenboom
<linux@xxxxxxxxxxxxxx> wrote:
> Hello Weidong,
> The problem is most vendor's just don't fix it and ignore the problem 
> completely.
> Most often hiding them selves behind: come back when it's a problem with 
> Microsoft Windows, that the only single thing we support (and no other 
> software, so no vmware, no xen, no linux, perhaps even no hypervisor)

Supermicro were fairly cooperative but they wanted to know *exactly*
what was wrong, i.e. wanted me to show them the incorrect values and
how to fix them, I tried to work it out but failed :(.

I had the same problem on a Dell system, who went down the "we dont
support xen" route, but again they would have been willing to take it
further if I could show them which values were incorrect.

If we had a diagnostic tool that could verify the settings and output
detailed explanations of any problems that would really help to give
manufacturers the info they need to fix the bios.


> Well I don't know if the virtual pc in windows 7 supports an iommu now, but 
> it didn't in the past as far as i know, so any complain bounces off, and 
> there it all seems to end for them.
> Besides that i don't know if they do know what the problems with there 
> implementation in BIOS is when someone reports it.
> I think some behind the scenes pressure from Intel to vendors might help to 
> solve some of them.
> (my Q35 chipset, "Intel V-PRO" marketed motherboard (so much for that) also 
> suffers RMRR problem when another graphics card is inserted which switches 
> off the IGD).
> Although i think in my case your patch will work around that for me. Perhaps 
> a third option is needed, which does all the workarounds possible and warns 
> about potential security problem when requested ?
> --
> Sander
> Thursday, January 21, 2010, 1:46:39 PM, you wrote:
>> Noboru Iwamatsu wrote:
>>> Hi Weidong,
>>> I re-send the DRHD-fix patch.
>>> If DRHD does not have existent devices, ignore it.
>>> If DRHD has both existent and non-existent devices, consider it invalid
>>> and not register.
>> Although you patch workarounds your buggy BIOS, but we still need to
>> enable it for security purpose as I mentioned in previous mail. We
>> needn't workaround / fix all BIOS issues in software. I think security
>> is more important for this specific BIOS issue. Did you report the BIOS
>> issue to your OEM vendor? maybe it's better to get it fixed in BIOS.
>> Regards,
>> Weidong
>>> According to this patch and yours, my machine successfully booted
>>> with vt-d enabled.
>>> Signed-off-by: Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>
>>>> Keir Fraser wrote:
>>>>> On 21/01/2010 10:19, "Weidong Han" <weidong.han@xxxxxxxxx> wrote:
>>>>>>> Sorry this is typo.
>>>>>>> I mean:
>>>>>>> So, I think RMRR that has no-existent device is "invalid"
>>>>>>> and whole RMRR should be ignored.
>>>>>> looks reasonable.
>>>>>> Keir, I Acks Noboru's rmrr patch. Or do you want us to merge them to one
>>>>>> patch?
>>>>> Merge them up, re-send with both sign-off and acked-by all in one email.
>>>>> Thanks,
>>>>> Keir
>>>> Sorry, I disagree with Noboru after thinking it again. If the RMRR has
>>>> both no-existent device and also has existent devices in its scope, we
>>>> should not ignore it because the existent devices under its scope will
>>>> be impacted without the RMRR. so I suggest to print a warning instead of
>>>> ignore it. Attached a patch for it.
>>>> Signed-off-by: Weidong Han <weidong.han@xxxxxxxxx>
> --
> Best regards,
>  Sander                            mailto:linux@xxxxxxxxxxxxxx
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