From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?ISO-8859-1?Q?G=E1bor_P=C9K?= <pek@crysys.hu>
Subject: direct PIO/MMIO access
Date: Fri, 15 Feb 2013 17:31:55 +0100
Message-ID: <511E62FB.90804@crysys.hu>
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Hi all,

I would like to access the configuration registers of my passthrough
device from my HVM guest under Xen 4.2 via MMIO/PIO directly. Is there
any option for this in the config file of the guest? I know about the
ioports=[''] option for PIO accesses, but is there any way to do the
same with MMIO BAR registers? As far as I know the permissive flag works
only for PV guests. Does the ioports option allow direct access to
config space (0xcf8-0xcfc)? According to in xen/arch/x86/trap.c it is
not allowed.

    /*
     * Port 0xcf8 (CONFIG_ADDRESS) is only visible for DWORD accesses.
     * We never permit direct access to that register.
     */

What about Dom0?

Thank you!
-gabor