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Current Xen design is that the guest domain have readonly
access to the memory mapped for them. Documentation say it is not
safe for them to be writable. Why?
Is it so as to trigger a trap exception whenever writing is
made to it? This is the optimal answer :-).
And since it is not "safe" what checks are done in Xen
hypervisor against these "dangers", ie, enumerate the potential
dangers? I cannot think of any, as a newbie in Xen. My
logic is that if the pages have been assigned as owned by a domain, just let it
do whatever it wants to, and so therefore should not trigger any privilege trap
condition (or VM exit condition, in the HVM case).
In the traditional Linux model, once a memory is mapped for
user process, non-root user included, it can be mapped as
writable. So why is this discrepancy in the case of
Xen?
By taking away this readonly restriction, I think Xen
hypervisor will have a lot of performance to gain.
Please share your thoughts? Apologies for the
questions from a newbie.
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