Re: [Xen-devel] [PATCH v4 5/8] ioreq-server: add support for multiple servers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.14 at 14:49, <Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2014-04-09 at 13:43 +0100, Jan Beulich wrote:
>> >>> On 02.04.14 at 17:11, <paul.durrant@xxxxxxxxxx> wrote:
>> > Secondary servers use guest pages to communicate with emulators, in
>> > the same way as the default server. These pages need to be in the
>> > guest physmap otherwise there is no suitable reference that can be
>> > queried by an emulator in order to map them. Therefore a pool of
>> > pages in the current E820 reserved region, just below the special
>> > pages is used. Secondary servers allocate from and free to this pool
>> > as they are created and destroyed.
>> 
>> Ah, here is the answer to the question I raised on patch 6 - somehow
>> I managed to look at them in wrong order. Nevertheless, and also in
>> the context of the discussion we had with Stefano yesterday, we may
>> want/need to think of a way to allow pages to be trackable without
>> being mapped in the physmap.
> 
> Is what is wanted a new XENMAPSPACE which could be used via
> xen_add_to_physmap_batch to map foreign_dom.idx where idx for that
> mapspace is the ioreq page index rather than a gfn?

Something along those lines at least; the precise one you talk about
would help the other (qemu) issue - we'd really need a "free floating"
map space, with indexes assigned as they get removed from physmap
or allocated without putting them into the physmap.

Jan


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