RE: [PATCH v1 02/13] xen/arm: introduce a special domain DOMID_SHARED

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 18 Mar 2022, Penny Zheng wrote:
> > On Fri, 11 Mar 2022, Penny Zheng wrote:
> > > From: Penny Zheng <penzhe01@xxxxxxxxxxxxxxxxxxxxxxxx>
> > >
> > > In case to own statically shared pages when owner domain is not
> > > explicitly defined, this commits propose a special domain
> > > DOMID_SHARED, and we assign it 0x7FF5, as one of the system domains.
> > >
> > > Statically shared memory reuses the same way of initialization with
> > > static memory, hence this commits proposes a new Kconfig
> > > CONFIG_STATIC_SHM to wrap related codes, and this option depends on
> > static memory(CONFIG_STATIC_MEMORY).
> > 
> > Why does it depend on CONFIG_STATIC_MEMORY? This is a genuine question,
> > I am not trying to scope-creep the series. Is there an actual technical
> > dependency on CONFIG_STATIC_MEMORY? If not, it would be super useful to
> > be able to share memory statically even between normal dom0less guests (of
> > course it would be responsibility of the user to provide the right 
> > addresses and
> > avoid mapping clashes.) I know that some of our users have requested this
> > feature in the past.
> > 
> 
> I may find a proper way to rephrase here. My poor English writing skill...
> When I implemented domain on static allocation, statically configured guest 
> RAM is
> treated as static memory in Xen and I introduced a few helpers to 
> initialize/allocate/free
> static memory, like acquire_staticmem_pages, etc, and all these helpers are 
> guarded with
> CONFIG_STATIC_MEMORY. 
> I want to reuse these helpers on static shared memory, so CONFIG_STATIC_SHM 
> depends
> on CONFIG_STATIC_MEMORY.
> 
> So I'm not restricting sharing static memory between domain on static 
> allocation, current
> Implementation is also useful to normal dom0less guests.

Ah, excellent! That makes sense.