Re: [Xen-devel] [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.06.16 at 12:15, <george.dunlap@xxxxxxxxxx> wrote:
> On 22/06/16 11:10, Jan Beulich wrote:
>>>>> On 22.06.16 at 11:47, <george.dunlap@xxxxxxxxxx> wrote:
>>> So you're afraid of this sequence of events?
>>> 1) Server A de-registered, triggering a ioreq_server -> ram_rw type change
>>> 2) gfn N is marked as misconfigured
>>> 3) Server B registers and marks gfn N as ioreq_server
>>> 4) When N is accessed, the misconfiguration is resolved incorrectly to
>>> ram_rw
>>>
>>> But that can't happen, because misconfigured entries are resolved before
>>> setting a p2m entry; so at step 3, gfn N will be first set to
>>> (non-misconfigured) ram_rw, then changed to (non-misconfigured)
>>> ioreq_server.
>>>
>>> Or is there another sequence of events that I'm missing?
>> 
>> 1) Server A marks GFN Y as ioreq_server
>> 2) Server A de-registered, triggering a ioreq_server -> ram_rw type
>>    change
>> 3) Server B registers and gfn Y still didn't become ram_rw again (as
>>    the misconfiguration didn't trickle down the tree far enough)
> 
> There are some missing steps here.  Gfn Y is still misconfigured, right?
>  What will happen when the misconfiguration is resolved?  Will it not
> become ram_rw?  If not, what would it change to and why?

Oh, right, of course.

Jan


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