Re: [Xen-devel] Why gpa instead of mfn is directed used in emulated nic

[openlui <openlui@xxxxxxx>]

At 2015-03-05 19:09:41, "Tim Deegan" <tim@xxxxxxx> wrote:
>Hi,
>
>At 10:54 +0800 on 05 Mar (1425549262), openlui wrote:
>> 2. From the trace info and qemu-dm's log, it seems that it is "GPA"
>> (Guest Physical Address) instead of "MFN" in the IOREQ's data field
>> received by qemu-dm:
>
>Yes.

Thanks for your reply.

>> I think qemu-dm/rtl8139 should read/write data from "MFN" address in
>> host memory instaed of GPA, and I find that there isn't hypercall
>> from dom0 to "translate" the gpa to mfn in subsequent xentrace
>> info. Is my understanding is wrong?  I would really appreciate your
>> help.
>
>The hypercall that qemu uses to map the guest's memory for reading and
>writing also takes a GFN/GPA.  So Qemu doesn't need to know what the
>actual MFN is -- it just does all its operations in GPAs and Xen takes
>care of the translations.

Could you give some hint about the type of hypercall qemu used to map the guest's memory? I know that there are some xc_map_foreign_xxx interfaces
in libxc which can do the similar work. However, it seems that these interfaces should be given MFN instead of GFN/GPA.

>Cheers,
>
>Tim.
>
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