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Re: [Xen-devel] (v2) Design proposal for RMRR fix

On 01/14/2015 02:42 PM, Jan Beulich wrote:
>>>> On 14.01.15 at 13:29, <george.dunlap@xxxxxxxxxxxxx> wrote:
>> On 01/14/2015 08:06 AM, Tian, Kevin wrote:
>>> We discussed earlier there are two reasons that some conflicts may not be 
>>> avoided:
>>>     - RMRRs conflicting with guest BIOS in <1MB area, as an example of 
>>> hard conflicts
>>>     - RMRRs conflicting with lowmem which is low enough then avoiding it
>>> will either break lowmem or make lowmem too low to impact guest (just
>>> an option being discussed)
>> So here you're assuming that we're going to keep the lowmem / mmio hole
>> / himem thing.  Is that necessary?  I was assuming that if we have
>> arbitrary RMRRs, that we would just have to accept that we'd need to be
>> able to punch an arbitrary number of holes in the p2m space.
> On the basis that the host would have placed the RMRRs in its MMIO
> hole, I think I agree with Kevin that if possible we should stick with
> the simpler lowmem / mmio-hole / highmem model if possible. If we
> really find this too limiting, switching to the more fine grained model
> later on will still be possible.

OK, sounds good.

One detail to work out in that case then is if / when we want to error
out or warn the user that the mmio hole is "too big" (or the RMRR is
"too low").

(I may think about it and post some thoughts tomorrow.)


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