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xen-devel
Re: [Xen-devel] Two question about grant table mechanism
On 19 Jun 2006, at 08:09, Lily Huang wrote:
First question:
If domA grant access permission of a page to DomB, and domB remapped
this page but then it crashes or failed to end mapping. Now domA wants
to end page granting, what will happen? Is there any way for page
owner to actively stop other VM's mapping?
No, it's expected you'll have an out-of-band mechanism for reclaiming
the mapping, probably involving killing the offending DomB. This makes
sense for the original usage scenario of driver domains, where if a
backend driver has gone bad or got hung, merely getting back any
current grants is unlikely to unstick things: you need a bigger hammer.
There's been discussion of other kinds of memory sharing mechanism
which wouldn't have this problem -- a domain puts some memory to one
side when it maps shared memory, which can then be revoked from under
its feet by mapping the memory it put to one side in the shared
memory's place. I think Rusty's patches implement something like this.
Second question:
If domA grant read-only permission on a page to domB, but domB tries
to write some data to this page. What will happen? General Memory
Protection?
DomB can only map the page read only, so write accesses will generate a
page fault.
-- Keir
These two questions are very important to my research. Can someone
give me a answer to direct me somewhere so that I can read more
details about grant table.
Many thanks!
-lily
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