Re: [Xen-devel] [v8][PATCH 06/16] hvmloader/pci: disable all pci devices conflicting with rdm

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 07/16/2015 04:20 PM, Chen, Tiejun wrote:
>>> What about this?
>>
>> Looks reasonable (but don't forget that I continue to be unconvinced
>> that the patch as a whole makes sense).
> 
> Yes, I always keep this in my mind as I mentioned in patch #00. Any risk
> you're still concerning? Is it that case if guest OS force enabling
> these devices again? IMO, at this point there are two cases:
> 
> #1. Without passing through a RMRR device
> 
> Those emulated devices don't create 1:1 mapping so its safe, right?
> 
> #2. With passing through a RMRR device
> 
> This just probably cause these associated devices not to work well, but
> still don't bring any impact to other Domains, right? I mean this isn't
> going to worsen the preexisting situation.
> 
> If I'm wrong please correct me.

But I think the issue is, without doing *something* about MMIO
collisions, the feature as a whole is sort of pointless.  You can
carefully specify rdm="strategy=host,reserved=strict", but you might
still get devices whose MMIO regions conflict with RMMRs, and there's
nothing you can really do about it.

And although I personally think it might be possible / reasonable to
check in a newly-written, partial MMIO collision avoidance patch, not
everyone might agree.  Even if I were to rewrite and post a patch
myself, they may argue that doing such a complicated re-design after the
feature freeze shouldn't be allowed.

 -George

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