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

[Tim Deegan <tim@xxxxxxx>]

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.

> 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.

Cheers,

Tim.

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