Re: [Xen-devel] [RFC][PATCH 4/5] tools:firmware:hvmloader: reserve RMRR mappings in e820

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.08.14 at 12:59, <tiejun.chen@xxxxxxxxx> wrote:
> On 2014/8/12 0:00, Tian, Kevin wrote:
>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>>> Sent: Sunday, August 10, 2014 11:53 PM
>>>>>> On 08.08.14 at 23:47, <kevin.tian@xxxxxxxxx> wrote:
>>>> strictly speaking besides reserving in e820, you should also poke later
>>>> MMIO BAR allocations to avoid confliction too. Currently it's relative
>>>> to low_mem_pgend, which is likely to be different from host layout
>>>> so it's still possible to see a virtual MMIO bar base conflicting to the
>>>> RMRR ranges which are supposed to be sparse.
>>>
>>> Correct. And what's worse: Possible collisions between RMRRs and
>>> the BIOS we place into the VM need to be taken care of, which may
>>> turn out rather tricky.
>>>
>>
>> right that becomes tricky. We can provide another hypercall to allow a
>> VM tell Xen which RMRR can't be assigned due to confliction with gust
>> BIOS or other hvmloader allocation (if confliction can't be resolved).
>>
>> If Xen detects a device owning RMRR is already assigned to the VM,
>> then fail the hypercall and hvmloader just panic with information to
>> indicate confliction.
>>
>> Otherwise Xen records the information and future dynamic device
>> assignment like hotplug will be failed if associated RMRR will be in
>> the confliction list.
> 
>  From my point of view its becoming over complicated.
> 
> In HVM case, theoretically any devices involving RMRR may be assigned to 
> any given VM. So it may not be necessary to introduce such complex 
> mechanism. Therefore, I think we can reserve all RMRR maps simply in 
> e820, and check if MMIO is overlapping with RMRR for every VM. It should 
> be acceptable.

Then you didn't understand what Kevin and I said above. Just
keep in mind that the RMRRs can conflict not just with MMIO
ranges inside the guest, but also RAM ranges (which include, as
mentioned above, the range where the BIOS for the guest gets
put).

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel