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Date: Mon, 1 Mar 2010 13:26:37 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] VirtIO: Fix QEMU crash during Windows PNP
	tests
Message-ID: <20100301112637.GH16909@redhat.com>
References: <1252935086-8856-1-git-send-email-yvugenfi@redhat.com>
	<BAEAF048-3CD5-4F5E-B938-DBB751F35318@suse.de>
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To: Alexander Graf <agraf@suse.de>
Cc: Yan Vugenfirer <yvugenfi@redhat.com>, "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, "Michael S. Tsirkin" <mst@redhat.com>

On Mon, Mar 01, 2010 at 12:14:43PM +0100, Alexander Graf wrote:
> 
> On 14.09.2009, at 15:31, Yan Vugenfirer wrote:
> 
> > Signed-off-by: Yan Vugenfirer <yvugenfi@redhat.com>
> > 
> > ---
> > hw/virtio-pci.c |   14 ++++++++++++--
> > 1 files changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> > index f812ab7..a0a22c4 100644
> > --- a/hw/virtio-pci.c
> > +++ b/hw/virtio-pci.c
> > @@ -364,8 +364,17 @@ static void virtio_map(PCIDevice *pci_dev, int region_num,
> > static void virtio_write_config(PCIDevice *pci_dev, uint32_t address,
> >                                 uint32_t val, int len)
> > {
> > +    VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
> > +
> > +    if (PCI_COMMAND == address) {
> > +        if (!(val & PCI_COMMAND_MASTER)) {
> > +            proxy->vdev->status &= ~VIRTIO_CONFIG_S_DRIVER_OK;
> 
> This part breaks PCI hotplug with Linux guests.
> 
> What happens is the following:
Looks like something is broken even without this patch.

> 
> (qemu) pci_add auto nic model=virtio,vlan=0
>   - Virtio dev 1 -> write config (0)
>   - Virtio dev 1 -> write config (0x3)
>   - Virtio dev 1 -> set status explicitly to OK
Why Linux doesn't enable bus mastering on this device?

> 
> (qemu) pci_add auto storage file=/tmp/image.raw,if=virtio
>   - Virtio dev 1 -> write config (0x3)
Why Linux touches unrelated device's config space?

>   -> Unset DRIVER_OK bit
>   -> network device becomes unresponsive 
>   - Virtio dev 2 -> write config (0)
>   - Virtio dev 2 -> write config (0x3)
>   - Virtio dev 2 -> set status explicitly to OK
> 
> 
> Please either revert this patch or provide a proper fix.
> 
> Alex

--
			Gleb.