Re: [Xen-devel] address mapping between domains

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> 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).

> 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.

Cheers,
Mark

>
> Thanks a lot.
>
> --------------------------
> Zhiyi from EPFL Switzerland
>
>
>
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