ia64/xen-unstable

changeset 18460:1f89af507e62

vtd.txt: Add caveat about assigning certain types of device.

From: Yuji Shimada <shimada-yxb@necst.nec.co.jp>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Sep 09 14:54:56 2008 +0100 (2008-09-09)
parents 5ce9459ce872
children 4f27d1a23bca
files docs/misc/vtd.txt
line diff
     1.1 --- a/docs/misc/vtd.txt	Tue Sep 09 14:50:29 2008 +0100
     1.2 +++ b/docs/misc/vtd.txt	Tue Sep 09 14:54:56 2008 +0100
     1.3 @@ -1,8 +1,9 @@
     1.4  Title   : How to do PCI Passthrough with VT-d
     1.5  Authors : Allen Kay    <allen.m.kay@intel.com>
     1.6            Weidong Han  <weidong.han@intel.com>
     1.7 +          Yuji Shimada <shimada-yxb@necst.nec.co.jp>
     1.8  Created : October-24-2007
     1.9 -Updated : August-06-2008
    1.10 +Updated : September-09-2008
    1.11  
    1.12  How to turn on VT-d in Xen
    1.13  --------------------------
    1.14 @@ -106,3 +107,27 @@ http://h10010.www1.hp.com/wwpc/us/en/en/
    1.15  
    1.16  For more information, pls refer to http://wiki.xensource.com/xenwiki/VTdHowTo.
    1.17  
    1.18 +
    1.19 +Assigning devices to HVM domains
    1.20 +--------------------------------
    1.21 +
    1.22 +Most device types such as NIC, HBA, EHCI and UHCI can be assigned to
    1.23 +an HVM domain.
    1.24 +
    1.25 +But some devices have design features which make them unsuitable for
    1.26 +assignment to an HVM domain. Examples include:
    1.27 +
    1.28 + * Device has an internal resource, such as private memory, which is
    1.29 +   mapped to memory address space with BAR (Base Address Register).
    1.30 + * Driver submits command with a pointer to a buffer within internal
    1.31 +   resource. Device decodes the pointer (address), and accesses to the
    1.32 +   buffer.
    1.33 +
    1.34 +In an HVM domain, the BAR is virtualized, and host-BAR value and
    1.35 +guest-BAR value are different. The addresses of internal resource from
    1.36 +device's view and driver's view are different. Similarly, the
    1.37 +addresses of buffer within internal resource from device's view and
    1.38 +driver's view are different. As a result, device can't access to the
    1.39 +buffer specified by driver.
    1.40 +
    1.41 +Such devices assigned to HVM domain currently do not work.