Re: Re: [Xen-devel] address mapping between domains

[Zhiyi Huang <zhiyi6@xxxxxxxxxx>]

Thanks, Chris and Mark.
Yes, I understand and appreciate the security issue between domains. Since I am 
considering a shared memory device in domain0, I really need a mechanism to map 
pages in domain0 to address space of a domainU.

> > Hi, I am trying to figure out how address mapping is done for zero-copy
> > I/O. Is it allowed by the hypervisor that a page allocated to domain0 (the
> > privileged domain) is mapped to the address space of a domainU? So far it
> > seems to be the other way around: a page from a domainU is mapped to the
> > address space of domain0 when I/O requests are sent to domain0.
> 
> The domain that's controlling the real device (usually dom0) maps the domU's 
> memory before putting data into it (either directly or using PIO).

Can I use this mechanism to make domU to share some pages in dom0? Where can I 
find the code, please?

> > Another question is about the hypercall: update_va_mapping. It has three
> > arguments: vaddr, val, flags. Can anyone kindly explain the meaning of them
> > and how they are used in the hypercall? Actually I am puzzled why there is
> > no machine page id as an argument, since the virtual address should be
> > mapped to a machine page anyway when the page table is updated.
> 
> Arguments to this as as Chris described.
> 
> Note that the backend drivers often use a "multicall" to perfrom multiple 
> operations (e.g. update multiple address mappings) in one hypercall.

Yes, I have noticed it. Thanks a lot for help.

--------------------------
Zhiyi from EPFL Switzerland



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