RE: [Xen-devel] event_lock not initialized in the idle domain (permitted actions in a tasklet?)

["Byrne, John (HP Labs)" <john.l.byrne@xxxxxx>]

> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> ...snipped...
> I think your approach of removing the tasklet was the correct one. See
> arch/x86/hvm/hvm.c:hvm_send_assist_req() for an example of correct
> usage of
> the *_xen_event_channel() helpers. Firstly, that function doesn't run
> as a
> tasklet; Secondly, in fact 'v' *always* is current. Possibly we should
> even
> ASSERT that on entry to the function to make it clearer.
> 
> I think that the correct functions probably are being used, just in the
> wrong context. The aim after all is to pause the current vcpu until it
> receives assistance from a helper in dom0. That is similar to the
> existing
> (correct) use of *_xen_event_channel() which is to pause an HVM vcpu
> which
> requires help from qemu-dm in a stubdomain or dom0 process.

Keir,

Unfortunately, in the page sharing case as of now, p2m_mem_paging_populate() 
(which will eventually want to send the event) can be called from dom0 in the 
grant code. (Maybe you can see a way to re-engineer this, but it is not obvious 
to me.)  So, I need an interface that allows me to specify the domain. I don't 
see one for Xen event channels and the cleanest way I see to implement this is 
to simply add one. I'm certainly open to suggestions.

The handling in the grant code for paging is pretty ugly. There are a couple of 
holes. The biggest is that I don't see an obvious way to keep mapped grant 
pages from being evicted, again. However, I think it will work well enough for 
me to test what I need.

John




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