Re: [Xen-devel] feature suggestion: DMAR table emulation for Xen

[Barde Kaushik 00901718 <kbarde@xxxxxxxxxx>]

<< So, if we took a DMAR from a platform, say PM45+ICH9M w/ Intel BIOS, it
should also work fine on any other laptop with this chipset (and
probably other variants too), just minus the potential
BIOS-specific-dirty-tricks...?
>>

Bringing-up mobile variants with same base BIOS may not work, at least in my 
experience, as OEMs tend to add various custom features (GPIO). These features 
may to over-ride RMRR assumptions from base BIOS. This tends to be the most 
prominant cause behind RMRR issues.

-Kaushik



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----- Original Message -----
From: Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
Date: Friday, May 14, 2010 2:20 am
Subject: Re: [Xen-devel] feature suggestion: DMAR table emulation for Xen
To: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
Cc: "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" 
<xen-devel@xxxxxxxxxxxxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>

> On 05/14/2010 07:41 AM, Kay, Allen M wrote:
> > Joanna,
> > 
> > RMRR memory ranges specified memory ranges that might be used for
> > BIOS initiated DMA's for USB and integrated graphics devices.  These
> > ranges are set by the BIOS.
> > 
> > Do they stay the same across different platforms?
> > 
> 
> To be frank, those RMRR ranges have always been a bit of a mystery for
> me. Do you actually know any OS drivers for USB devices that would
> depend on them? Aren't they only used by the BIOS to implement various
> dirty tricks they like to implement?
> 
> The Intel VT-d spec says that: "USB controllers and UMA integrated
> graphics devices are the only legacy device usages identified
> that depend on DMA to reserved system memory".
> 
> I think we can safely ignore the legacy integrated graphics devices,
> because I would expect any VT-d enabled platform to have a modern
> graphics device and modern OS drivers that works well with VT-d (you
> even provide a dedicated DMA Remapping Unit for your integrated 
> graphicsdevice, so I would expect it doesn't require any RMMR 
> exceptions).
> So USB devices seem to be the only potential problem. But USB devices
> are implemented by the ICH, which in most cases is Intel ICH9, or 10.
> So, if we took a DMAR from a platform, say PM45+ICH9M w/ Intel 
> BIOS, it
> should also work fine on any other laptop with this chipset (and
> probably other variants too), just minus the potential
> BIOS-specific-dirty-tricks...?
> 
> joanna.
> 
> 

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