Re: [Xen-devel] [V7 PATCH 5/7] pvh: change xsm_add_to_physmap

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sun, 2014-02-09 at 16:51 +0000, Julien Grall wrote:
> Hello Mukesh,
> 
> On 30/01/14 01:33, Mukesh Rathor wrote:
> >>> I'm not sure what you mean:
> >>>   - the code that Mukesh is adding doesn't have a struct page, it's
> >>>     just grabbing the foreign domid from the hypercall arg;
> >>>   - if we did have a struct page, we'd just need to take a ref to
> >>>     stop the owner changing underfoot; and
> >>>   - get_pg_owner() takes a domid anyway.
> >>
> >> Sorry, I was confused/mislead by the name...
> >>
> >> rcu_lock_live_remote_domain_by_id does look like what is needed.
> 
> Following the xentrace tread: 
> http://www.gossamer-threads.com/lists/xen/devel/315883, 
> rcu_lock_live_remote_domain_by_id will not correctly works.
> 
> On Xen on ARM, xentrace is using this hypercall to map XEN page (via 
> DOMID_XEN). In this case, rcu_lock_*domain* will always fails which will 
> prevent xentrace to works on Xen on ARM (and on PVH).

I'm not sure how that extends to add_to_physmap though -- doing add to
physmap of a DOMID_XEN owned page through the "back door" in this way
isn't supposed to work.

Ian.


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