Re: [Qemu-trivial] [Qemu-devel] [PATCH] Remove PCI class code from virtio balloon device

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Mar 19, 2012 at 03:59:23PM +1100, David Gibson wrote:
> Currently the virtio balloon device, when using the virtio-pci interface
> advertises itself with PCI class code MEMORY_RAM.  This is wrong; the
> balloon is vaguely related to memory, but is nothing like a PCI memory
> device in the meaning of the class code, and this code is not required or
> suggested by the virtio PCI specification.
> 
> Worse, this patch causes problems on the pseries machine, because the
> firmware, seeing this class code, advertises the device as memory in the
> device tree, and then a guest kernel bug causes it to see this "memory"
> before the real system memory, leading to a crash in early boot.
> 
> This patch fixes the problem by removing the bogus PCI class code on the
> balloon device.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/virtio-pci.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)

Since this is a guest-visible change we might need to be careful about
how it's introduced.

Do we need to keep the old class code for existing machine types?  The
new class code could be introduced only for 1.1 and later machine types
if we want to be extra careful about introducing guest-visible changes.

Michael: Do you want to take it through your tree?

Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>