On Thu, 1 Nov 2018, Julien Grall wrote: > Hi, > > On 11/1/18 8:31 PM, Stefano Stabellini wrote: > > On Wed, 31 Oct 2018, Julien Grall wrote: > > > Hi, > > > > > > On 10/24/18 2:18 AM, Stefano Stabellini wrote: > > > > From: Stefano Stabellini <stefanos@xxxxxxxxxx> > > > > > > > > Introduce a device tree binding for Xen reserved-memory regions. They > > > > are used to share memory across VMs from the VM config files. (See > > > > static_shm config option.) > > > > > > > > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx> > > > > Cc: julien.grall@xxxxxxx > > > > --- > > > > Changes in v3: > > > > - remove fallback version > > > > > > > > Changes in v2: > > > > - fix Author line > > > > - add versioning > > > > - xen,id instead of id > > > > --- > > > > .../bindings/reserved-memory/xen,shared-memory.txt | 20 > > > > ++++++++++++++++++++ > > > > 1 file changed, 20 insertions(+) > > > > create mode 100644 > > > > Documentation/devicetree/bindings/reserved-memory/xen,shared-memory.txt > > > > > > > > diff --git > > > > a/Documentation/devicetree/bindings/reserved-memory/xen,shared-memory.txt > > > > b/Documentation/devicetree/bindings/reserved-memory/xen,shared-memory.txt > > > > new file mode 100644 > > > > index 0000000..7c81683 > > > > --- /dev/null > > > > +++ > > > > b/Documentation/devicetree/bindings/reserved-memory/xen,shared-memory.txt > > > > @@ -0,0 +1,20 @@ > > > > +* Xen hypervisor reserved-memory binding > > > > + > > > > +Expose one or more memory regions as reserved-memory to the guest > > > > +virtual machine. Typically, a region is configured at VM creation time > > > > +to be a shared memory area across multiple virtual machines for > > > > +communication among them. > > > > > > I may have notice some issue with this binding. Looking at the design > > > document > > > [1], the "master" domain may provide a big backing region that would be > > > split > > > and share with multiple "slave". > > > > > > For the "master" domain, this binding would specify the full backing > > > region. > > > The "master" OS would not be able to know how the region would be used > > > here. > > > > > > For the "slave" domain, it looks like it might be possible to map the same > > > region (so same ID) twice. So we would end up to create the same bindings > > > twice. > > > > > > Any opionion on how we should proceed with these two use cases? > > > > Julien and I discussed this morning to clarify that regions shouldn't be > > mapped twice in the Xen docs, and adding an "offset" property to this > > binding. > > Well, why would you forbid the mappings twice if the offset is present? >From the DT binding point of view, it would be fine. Conceptually it would also be fine. However, I doubt that the current libxl implementation would work with multiple mappings.
