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RE: [Xen-devel] About IO

To: "Liu, Huahang" <huahang.liu@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] About IO
From: "Guy Zana" <guy@xxxxxxxxxxxx>
Date: Fri, 30 Mar 2007 04:01:31 -0400
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Thread-topic: [Xen-devel] About IO
When a guest access a pseudo physical memory address, the hypervisor tries to translate it to the equivalent machine address (real memory). If the address does not exist in the guets's P2M (physical to machine) translation then it is considered to be mmio, in this case, a ioctl_t struct representing that access is being built and sent to the device model of the HVM guest in domain0, there it is handled by the emulated hardware.
Non-prefetchable MMIO (buffered) regions are being mapped to the guest's memory layout and they actually a part of it.
Since it is not prefetchable, a buffered mmio region is also mapped to the device model and being accessed "randomly", preformance is better this way.

From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Liu, Huahang
Sent: Friday, March 30, 2007 6:28 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] About IO


What is the MMIO address space of Xen HVM?

What happen when I read from or write to these IO ports?




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