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Re: [Qemu-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 f

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [v2][PATCH 4/8] xen, gfx passthrough: reserve 00:02.0 for INTEL IGD
Date: Mon, 19 May 2014 08:44:47 +0200


> +    /*
> +     * 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


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