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Re: [Qemu-devel] [Xen-devel] [v2][PATCH 4/8] xen, gfx passthrough: rese

From: Fabio Fantoni
Subject: Re: [Qemu-devel] [Xen-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 for INTEL IGD
Date: Mon, 19 May 2014 09:48:02 +0200
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

Il 19/05/2014 08:44, Gerd Hoffmann ha scritto:

+    /*
+     * Some video bioses and gfx drivers will assume the bdf of IGD is 00:02.0.
+     * So user need to set it to 00:02.0 in Xen configure file explicitly,
+     * otherwise IGD will fail to work.
+     */
+    pci_reserve_pci_devfn(b, PCI_DEVFN(2, 0));
That is asking for trouble.  Slot 2 is used by the qemu vga cards by
default, and for quite a while (before memory api was merged) it even
was impossible to change it.  libvirt still places the vga card at slot
2 for that reason -> boom.  I wouldn't be surprised if you find that
assumption in other management libs / apps too.

Why do you need that patch in the first place?  It should be possible to
configure qemu to not occupy slot 2 if you need it that way.  Just pass
'-vga none' to qemu.  Which you probably want anyway if you pass-through
a vga to the guest.  And explicitly configure a slot (via addr=
property) for all your pci devices.  Doing it only for the IGD works too
if you list the device before any other pci device on the qemu command


I already added vga none support on libxl, useful also for this cases:

This patch is already tested and working, for now I not tested and I can't test with intel gpu passthrough, someone can test it with intel gpu passthrough?

Thanks for any reply and sorry for my bad english.

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